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The potential of biofuels from first to fourth generation
Contributed equally to this work with: Philipp Cavelius, Selina Engelhart-Straub
Roles Conceptualization, Data curation, Investigation, Validation, Visualization, Writing – original draft, Writing – review & editing
Affiliation Werner Siemens-Chair of Synthetic Biotechnology, TUM School of Natural Sciences, Technical University of Munich (TUM), Garching, Germany
Roles Conceptualization, Data curation, Funding acquisition, Project administration, Supervision, Writing – original draft, Writing – review & editing
Roles Conceptualization, Data curation, Supervision, Writing – review & editing
Affiliation Chair of Technical Chemistry II, TUM School of Natural Sciences, Technical University of Munich (TUM), Garching, Germany
Roles Conceptualization, Data curation, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing
* E-mail: [email protected] (DA); [email protected] (TB)
- Philipp Cavelius,
- Selina Engelhart-Straub,
- Norbert Mehlmer,
- Johannes Lercher,
- Dania Awad,
- Thomas Brück
Published: March 30, 2023
- https://doi.org/10.1371/journal.pbio.3002063
- Reader Comments
The steady increase in human population and a rising standard of living heighten global demand for energy. Fossil fuels account for more than three-quarters of energy production, releasing enormous amounts of carbon dioxide (CO 2 ) that drive climate change effects as well as contributing to severe air pollution in many countries. Hence, drastic reduction of CO 2 emissions, especially from fossil fuels, is essential to tackle anthropogenic climate change. To reduce CO 2 emissions and to cope with the ever-growing demand for energy, it is essential to develop renewable energy sources, of which biofuels will form an important contribution. In this Essay, liquid biofuels from first to fourth generation are discussed in detail alongside their industrial development and policy implications, with a focus on the transport sector as a complementary solution to other environmentally friendly technologies, such as electric cars.
Citation: Cavelius P, Engelhart-Straub S, Mehlmer N, Lercher J, Awad D, Brück T (2023) The potential of biofuels from first to fourth generation. PLoS Biol 21(3): e3002063. https://doi.org/10.1371/journal.pbio.3002063
Copyright: © 2023 Cavelius et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was supported by the German Federal Ministry of Education and Research (BMBF) (031B0853A to NM). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Abbreviations: EEA, European Environment Agency; EIC, European Innovation Council; GHG, greenhouse gas; GMO, genetically modified organism; ILUC, indirect land use change; IPCC, Intergovernmental Panel on Climate Change; IRENA, International Renewable Energy Agency; RED, Renewable Energy Directive
Introduction
For decades, global energy demand is on the rise due to economic growth and a rapidly growing world population. Additionally, the standard of living is increasing worldwide, in most cases correlating with increased energy consumption, as energy is needed in almost every aspect of our lives, including land, water, and air transport as well as in agriculture, commercial, industrial, and domestic sectors [ 1 ]. To date, fossil fuels account for around 80% of the world’s energy demand [ 2 ], despite being a major instigator for global warming, representing roughly 89% of total greenhouse gas (GHG) emissions in 2020 [ 3 ]. Additionally, fossil fuels are predicted to deplete with the steadily increasing energy demands. As petroleum demand is constantly on the rise, estimations predict a shortage by 2070 to 2080 [ 4 ]. To that end, distinct biofuel types such as liquid and biogas should be methodologically and strategically developed as a preventive measure against predicted energy shortages, all while reducing the anthropogenic climate impact and preserving the environment.
Currently, biofuels are categorized as first to fourth generation, depending on feedstock and/or biosynthetic platform (i.e., genetic engineering). In this Essay, we present comparative advantages and disadvantages among these categories, as well as fossil sources. Furthermore, the development of biofuel technologies hinges on the socioeconomic and political landscape, which can greatly benefit from policy recommendations by respective regulatory bodies. At present, the European Union has the most stringent biofuel legislation and the most ambitious climate impact goals. Hence, we focus on EU-centered development with respect to current biofuel technology platforms at various stages of industrial deployment, the legislative framework implemented in the EU, as well as policy recommendations that would accelerate academic breakthroughs toward industrial implementation. Although, our recommendations are EU-centric, many are also applicable on a global level.
The four generations of biofuels
One alternative to fossil fuels are biofuels, which originate from organic matter and therefore can be regrown and are termed renewable. Biofuels emit less GHGs and are in general more eco-friendly (non-toxic, sulfur-free, biodegradable) than their fossil fuel predecessors [ 5 ]. Biofuels contribute to the achievement of Sustainable Development Goals 7 (affordable and clean energy) and 13 (climate action) of the United Nations [ 6 ]. Global demand for biofuels is set to grow by 41 to 53 billion liters, or 28%, over 2021 to 2026 [ 7 ]. Typically, one can find four main types of biofuel discussed in the context of fermentation: biogas, bioethanol, biobutanol, and biodiesel. The physiochemical properties of these biofuels are compared to fossil-based fuels in Table 1 .
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https://doi.org/10.1371/journal.pbio.3002063.t001
Biogas formation is a fairly simple process that has been utilized for several decades. It includes four stages: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Mixed microorganisms consortia and waste streams are combined in a sealed fermentation system in the absence of oxygen. During the biogas production process, microorganisms hydrolyze waste materials into sugars, peptides and amino acids, fatty acids, and to some part into acetate and hydrogen. Afterwards, acidogenic bacteria convert those intermediate products into organic acids, mainly constituting acetic acid. In addition, they produce carbon dioxide and hydrogen. In the third step, acetogenesis, acetate is formed from hydrogen and carbon dioxide produced in the previous stage. Lastly, methanogenesis follows, creating methane from the products of acetogenesis and acidogenesis [ 8 ]. These gases can then be transformed into hydrogen and/or electricity, or can be stored as biomethane in existing geological reservoirs [ 9 ]. Since the Ukraine crisis began, the resulting lack of fossil fuel availability in the EU has led to biogas being politically pushed as a substitute to natural gas [ 10 ].
Compared to gas (biogas/hydrogen), liquid fuels offer higher energy density and simplified transport and storage. This renders them more compatible with current engine and turbine technologies [ 11 ]. Most engines and turbines are designed and built for the use of liquid fuels, which makes liquid biofuels an easy drop-in solution without the need for modifying present engine technologies or infrastructure [ 5 , 12 ]. These gaseous fuels pose a significant safety hazard as they ignite at lower energies and are flammable over a range of concentrations, hydrogen to higher extent, requiring high level of safety procedures [ 13 ]. The low boiling point and high octane number of bioethanol allow blending with gasoline to a certain extent. The added benefits include a more complete combustion and reduced tailpipe emissions, boosting the engine performance and reducing CO 2 emissions. It is, however, inapt for blending with diesel. Diesel engines require hydrocarbons of higher chain length and low autoignition temperature. However, biodiesel, being of similar chemical constitution, can be blended with fossil-based diesel and hence constitutes a major energy-dense liquid biofuel. A third increasingly attractive biofuel is biobutanol, which holds high promise as it displays superior properties to bioethanol such as higher energy density (25% more energy than ethanol) and usually lower water content due to increased hydrophobicity. Biobutanol is less volatile and possesses less corrosive properties, making it easier and safer to use and store [ 11 , 14 – 19 ]. More importantly, it can be blended with both gasoline, fossil-based or biodiesel at any ratio without the need of new engine technologies and might even allow complete substitution of gasoline, while the use of ethanol is only possible as additive [ 11 , 18 ].
While the classification of biofuel technologies somewhat varies in the literature, products can generally be classed as first to fourth generation, depending on the type of feedstock and conversion process that was applied ( Fig 1 ) [ 5 ].
https://doi.org/10.1371/journal.pbio.3002063.g001
First-generation biofuels
Biofuels of the first generation are mainly divided into bioethanol and biodiesel. Bioethanol production of the first generation is based on microbial fermentation of edible feedstocks, rich in starch and sucrose, such as wheat, corn, and sugarcane in Europe, North America, and South America, respectively. Commercial strains include but are not limited to Saccharomyces cerevisiae , S . stipites , and S . pombe . Bioethanol production is not limited to first-generation biofuels; depending on the feedstock and production strain, bioethanol can also be categorized as second and third generation [ 32 – 35 ]. Biodiesel is mainly obtained from food-grade rapeseed, soy, or palm oil sourced from Europe, South America, and Asia, respectively. In contrast to bioethanol, it is only partially biosynthesized as its production includes chemically catalyzed steps such as transesterification of the lipids with alcohols. Enzymatic catalysis currently only exists on a lab scale [ 36 , 37 ]. Although biobutanol production is also possible by sugar fermentation from sugar cane, corn, wheat, and other food crops, it is limited by lower productivity and yields, product inhibition, and high costs [ 11 , 16 , 18 , 38 ].
During the global food demand crisis in 2007/2008, crops used for biofuel became more important to be used as food, giving rise to the “food versus fuel” debate that persists to date. Additionally, an increased demand for crops (e.g., corn) for fuel production yielded an increased market price for those foods [ 5 ]. Models predict that massive agricultural areas would be needed for fuel production and still could supply only limited amounts of fuel compared to the overall demand. It is estimated that more than two times the globally available area of arable land would needed to meet the global market demand for biodiesel when produced from rapeseed oil [ 39 ]. Furthermore, increased market values of palm oil and other biofuel cultures prompted extended deforestation of tropical rainforests for biofuel crop plantations, which releases more CO 2 than the emission saved by those biofuels. In 2008, Fargione and colleagues estimated that it would take 319 years to repay the biofuel carbon debt resulting from clearing of tropical rainforest in Brazil and subsequent conversion to soybean plantations [ 40 ].
Second-generation biofuels
As a result of the issues of the first generation, second-generation biofuels were developed, utilizing lignocellulosic biomass from agricultural and woodland residues as well as other waste streams (for example, from food industry like wheat bran, animal fats, or wastes of cooking and frying oil). Other non-food plants like the drought-resistant shrub or tree Jatropha curcas , which can also be grown in wastelands, might yet be a different promising source for second-generation biofuels [ 41 ]. Hence, second-generation biofuels circumvent the need for agricultural land use change and do not compete with food resources. However, often second-generation waste streams represent more complex feedstocks than sugarcane or palm oil, potentially containing compounds able to reduce fermentation efficiency, such as lignin. Therefore, application of additional pretreatment steps are common, increasing process time and costs [ 5 , 42 , 43 ].
For the most part, biofuels of the first and in the vast majority of the second generation are commercially produced, around 4% and 96% in 2019, respectively [ 44 ]. One example is the commercially available sunliquid from Clariant, which is a cellulosic ethanol from currently underutilized agricultural residues, such as straw. The first commercial ethanol plant in Romania started production in 2022, with plans to convert 250,000 tons of locally sourced agricultural residues to 50,000 tons of ethanol per year. After enzyme production, which hydrolyses cellulose and hemicellulose to sugar monomers, optimized microorganisms are used in fermentation to produce ethanol. These microorganisms can utilize various carbon sources like glucose and xylose, ensuring higher yields and enabling high efficiency and flexibility in waste valorization as more building blocks of waste streams can be converted to product [ 45 ]. Alongside ethanol producers, the production of second-generation biodiesel is possible from microbial lipids produced by organisms, such as Cutaneotrichosporon oleaginosus , a yeast capable of producing up to 90% (w/w) lipids per biomass in a fermentation process, which can be grown on residue streams (e.g., wheat bran hydrolysate medium) [ 46 – 49 ]. Second-generation biodiesel can also be sourced from waste oils via catalytic cracking and hydrogenation. Drawbacks of this process include incomplete conversion and coke formation, which leads to the deactivation of the catalyst. [ 50 , 51 ]. Biobutanol production on lignocellulose biomass and other waste streams is most commonly based on Clostridia fermentation, as it is one of the oldest and best-established fermentative processes for butanol production. Many Clostridia are natural butanol producers and possess the ability to metabolize a variety of different substrates. However, similar to its first-generation predecessor, the process is limited by low butanol titers and product inhibition [ 11 , 16 , 18 , 38 ]. Typically, butanol is produced via ABE fermentation, which results in solvents in ratio of 3 parts acetone, 6 parts butanol, and 1 part ethanol, and butanol refinement is not an energetically favorable solution. Other drawbacks also include cell toxicity at low concentration [ 52 , 53 ]. To that end, cell-free isobutanol biosynthesis using a designed artificial metabolic pathway has been developed [ 54 ]. At present, this approach remains costly for commercialization.
Various carbonaceous compounds can be transformed to syngas by gasification. Commonly, it is a gaseous waste stream from industrial processes such as steel manufacture, in which fossil fuels are burned in the process. Syngas is a mixture mainly consisting of carbon monoxide (CO), CO 2 , and hydrogen. It can be derived from biomass, including lignocellulosic compounds, coal, animal or municipal solid waste, and industrial CO-rich gases. This gas can be metabolized by strictly anaerobic, methanogenic archaea as well as by acetogenic bacterial genera such as Acetobacterium or Clostridium , often used in syntrophic fermentations. The process is mostly focused on biosynthesis of organic acids and alcohol compounds such as acetate, ethanol, and butanol [ 55 – 57 ]. Advantages of syngas fermentation compared to other second-generation approaches are high feedstock flexibility as well as high rates of energy and carbon capture. Complicated pretreatments of second-generation feedstocks can be replaced with gasification, using all components of the biomass, including lignin and other recalcitrant compounds [ 58 ]. LanzaTech developed a process converting feedstocks including industrial waste streams to fuel and chemicals utilizing bacteria. They estimate a total product capacity of 600,000 metric tons as well as 1,000,000 metric tons of captured carbon per year, for all their plants combined [ 59 ]. Since 2022, a demonstration plant in Japan has turned municipal solid waste to ethanol, with a production target of 20 tons of ethanol per day [ 60 ].
More than half of the biologically stored carbon is bound in marine biomass, especially macroalgae and seagrass. Detached seagrass material is seasonally washed on beaches and shore lines; due to low biological degradation and herbivore consumption, an excess of it accumulates as waste. Estimations of up to 40 million tons of dry seagrass biomass, which can be used for biofuel production, are given. Through enzymatic hydrolysis, the carbohydrate content of the seagrass can be used in a fermentation medium for microorganisms, additionally offering low nitrogen and phosphorus content, which is typically required for lipid production [ 61 ].
Despite the highly favorable ability to valorize waste streams, second-generation biofuels by themselves will not be sufficient to supply energy for the current worldwide demand. As is the case for food crops with first-generation biofuels, biomass used in these processes is available in limited amounts. Therefore, second-generation biofuels must be combined with other technologies to ensure sufficient provision of fuels. This prompted research on third-generation biofuels. However, scientific estimations predict second-generation biofuels could supply up to 30% of the world’s transportation energy [ 5 ].
Third-generation biofuels
Third-generation biofuels are mainly derived from microalgae and cyanobacteria biomass, which can be used to naturally generate alcohols and lipids to transform into biodiesel or any other high energy fuel product. Algae exhibit 2- to 4-fold higher photosynthesis rates than terrestrial plants, resulting in faster biomass formation [ 62 ]. Algae do not require arable land or fresh water for cultivation. Many cultures can be grown using waste water, brackish or salt water, which is cost efficient and circumvents competition with agricultural activity [ 63 , 64 ]. Most importantly, efficient algae cultivation requires a direct CO 2 supply, which can be derived from industrial emitters or by atmospheric carbon capture. In conventional cultivation systems, around 70% of supplied CO 2 is used for photosynthesis and therefore biomass production [ 65 ]. Hence, algae biofuels potentially could have a negative carbon footprint as they directly bind the GHG in their biomass. One of the most prominent third-generation processes is the production of biodiesel or other energy density biofuels, such as biokerosene, using oleaginous microalgae [ 66 , 67 ].
One of the most economically critical and versatile operations in algal biofuel production is algae cultivation. Algal bioreactors ( Fig 2 ) are independent of location and climate, therefore can be operated almost irrespective of these factors. For low price, high volume products, such as biofuels, algae are commonly cultivated in open ponds. Open pond reactors are significantly cheaper in their construction and operation but have drawbacks like high loss of water through evaporation and lack of temperature control, which lowers biomass productivity. The alternative, preferred for high price, low volume products, such as cosmetic ingredients, is a closed photobioreactor, where process parameters can be precisely controlled, which often leads to higher productivity [ 63 , 68 ]. These bioreactors also enable a three-dimensional mode of cultivation, significantly increasing the productivity per area. In contrast to second-generation biofuels, the third-generation processes completely decouple biofuel production from the need for agricultural land. Additionally, algal-based oil production is likely greater than that in higher plants, as lipids mainly accumulate in specific parts of the plant (e.g., in rape seeds), while in algae, each cell can contain high amount of lipids, making the process more mass efficient. One bottleneck in production is harvesting, as the low size and density of the microalgal cells combined with the sensitivity of the cells to changes in pH render it challenging. [ 66 ]. Furthermore, downstream processing for algal biofuels is commonly more energy intensive than other biofuel productions [ 63 , 69 ]. Araújo and colleagues mapped 447 algae and cyanobacteria Spirulina production units in 2021 in the EU [ 70 ]. Most of these companies directed their biomass to the production of food, feed, and related uses; commercial application of biofuels only had a very small share. Further technological developments in upscaling and reduction of production costs are necessary for commercialization.
This image showcases the open algae cultivation systems located at Technical University of Munich, Ottobrunn.
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Fourth-generation biofuels
The latest biofuel generation, termed fourth-generation biofuels, encompasses the use of genetic engineering to increase desired traits of organisms used in biofuel production. This applies to a variety of traits from utilizing multiple types of sugars (e.g., pentoses and hexoses), to higher lipid synthesis or increased photosynthesis and carbon fixation. For model organisms, such as Escherichia coli and Saccharomyces cerevisiae , a wide variety of tools for genetically engineering the regulation of endogenous pathways or inserting new pathways are reported. Unfortunately, for most native producers of biofuels, the genetic engineering toolbox is far more limited.
Currently, two different approaches have been adopted: engineering of pathways in native producers (optimizing growth rates, utilization of different carbon sources, directing the metabolic flux toward biofuel production and increased production titers) and reconstruction of pathways identified in natural producers in more genetically accessible model organisms. A wide variety of microorganisms can be used as heterologous hosts for the production of biofuels, including bacteria, yeast, and algae. Their metabolic versatility enables the use of various substrates to produce a wide range of biofuels. For example, butanol pathway genes from Clostridia were introduced into E . coli , Pseudomonas putida , and Bacillus subtilis strains [ 14 , 16 , 19 ]. While the introduction of heterologous genes is well established, a major challenge is the disruption of competing metabolic fluxes. Another obstacle for high product titers can be toxicity of large amounts of product on the cell. To enable increased accumulation of biofuels, the cellular stress response can be modified through genetic engineering, for example, with cell membrane modifications. Through the overexpression of certain membrane transporters, biofuel molecules can be secreted into the medium thereby circumventing accumulation as well as toxicity while simultaneously simplifying product recovery. In E . coli , membrane transporters have been used successfully to excrete n-alkanes, such as n-octane [ 71 , 72 ]. However, the overexpression of transporters is challenging as it modifies the membrane composition, creating a metabolic burden as well as potentially overloading the cellular import and export, thereby disabling the cells ability to regulate its internal environment/homeostasis [ 71 ].
Genetically modified algae can offer higher product yields and a variety of other improvements compared to wild-type algae. In order to enhance photosynthetic efficiency, the antennae systems of algae capable of absorbing a broader range of the light spectrum could be transferred to more suitable production organisms [ 44 , 73 ]. With respect to genetic engineering, CRIPSR/Cas9 is a frequently used tool, as it offers a simple design with efficient transfection and targeted gene disruption [ 74 ].
In fourth-generation biofuel processes that focus on genetically optimized cyanobacteria, the production of ethanol, as well as other fuel products such as butanol, isobutanol, and modified fatty acids have been realized successfully [ 75 , 76 ]. While 1-butanol production reached titers of 300 mg/L, bioethanol titers of up to 5.5 g/L were reported [ 77 – 79 ].
For the efficient optimization of native producers, systems biology can offer many insights. The availability of whole-genome sequences is essential, as this information allows for the annotation of genes to their respective function and reconstruction of the innate metabolic pathways, which can subsequently be modified. Recent advances have been made in the field of genome sequencing allowing for a more rapid and cost-efficient collection of data [ 19 ], while the gene expression patterns in different growth environments can be analyzed by transcriptomics and protein products identified by proteomics.
With genetic engineering tools, the quantity and quality of biofuels can be controlled and increased but will need political acceptance and support to be widely adopted [ 5 ]. There is a controversial debate around genetic engineering in agriculture and medicine, especially in Europe; therefore, similar concerns can be anticipated surrounding the use in biofuel production. A European-based study came to the conclusion that genetically engineered algae for biofuel production would be accepted by the majority of consumers, when the safety of the systems can be guaranteed [ 80 ]. However, with proper containment methods and carefully selected locations, such risks could be drastically minimized. Therefore, closed production systems with high security standards are expected to be built [ 80 ]. Additional biocontainment methods can be directly based on genetic changes inside the production cells such as auxotrophies or kill switches, significantly decreasing the risk of genetically modified organism (GMO) escape [ 44 , 81 ].
One alternative to targeted genetic engineering is random mutagenesis, which can be described as accelerated evolution. Microorganisms and products generated by this approach are not subjected to GMO regulations. Furthermore, this technique can be performed with little knowledge about the production organism and production pathway. Random mutagenesis can be achieved by a variety of methods such as UV light, chemical agents, or fast neutron irradiation. For the first time, the latter was applied on C . oleaginosus , resulting in mutants with elevated lipid titers suitable for biodiesel applications. It is noteworthy that biodiesel from prominent oleaginous yeast platforms, such as Yarrowia lipolytica , C . oleaginosus , Rhodosporidium toruloides , and Lipomyces starkeyi , are compliant with international biodiesel standards, including US ASTM D6751 and EU standard EN 14214 [ 82 , 83 ].
A new, more experimental approach to fourth-generation biofuels is the production of electrobiofuels. These are based on the approach to establish new-to-nature hybrid systems, which are able to use renewable electricity and carbon sources directly for the production of commodity chemicals and biofuels, thereby enabling the conversion of solar energy into storable liquid fuel. Such a process could combine the higher photon efficiency of modern photovoltaic systems (compared to photosynthesis) with the sustainability of biofuel production, increasing overall process effectiveness [ 84 ].
Economics of biofuels in transportation
Apart from reducing GHG emissions and air pollution, biofuel industries can contribute to energy security on a local and national scale, as it is not reliant on local reservoirs of fossil oil. Additionally, the creation of new employment and economic growth, especially in rural locations, should positively impact the social environment as well. However, to fully exploit all the positive traits of biofuels, further research and investments are necessary, as the production of biofuels requires more processing steps compared with the conventional methods of drilling into the ground to obtain crude oil, followed by refining. Therefore, at present, biofuels commonly exceed fossil fuel production costs. Furthermore, raw materials for biofuel production do not compare to crude oil in energy density, requiring far greater amounts of biomass for the same energy output compared to fossil sources. The infrastructure required for the sector of biofuel production has to be extensively developed as well. One example is the primary energy needed to run the process, which should be obtained through sustainable operations. Candidates for that include solar and wind energy among others. Thus, by reducing the overall production cost and increasing process efficiency, biofuels could become more competitive to fossil fuels. Furthermore, by-products of biofuel production should be efficiently utilized in a circular economy, which could increase cost efficiency of such processes.
Transportation is one of the most socioeconomically sensitive sectors for the use of liquid biofuels ( Fig 3 ). It contributes about 17% of global CO 2 emissions [ 85 , 86 ], and so far, sustainable solutions are not fully developed. Due to their limitations, current technologies for biofuels are not likely to completely replace fossil fuels in their entirety but can offer new routes for waste stream valorization in a circular economy and contribute significantly to minimize our dependency on fossil fuels one step at a time. A complementary approach to this goal is electric cars, which have zero tailpipe emissions, although CO 2 emissions are associated with the production of the car and the source of the electricity. Essential in electric vehicle batteries are metals like lithium, cobalt, nickel, and manganese. The demand for these metals is surging, while at the same time toxic waste electronics are accumulating all over the world. Traditional recycling/extraction methods require high temperatures and strong acids. This is a high energy process involving toxic chemicals. One alternative is bioleaching or biomining, which employs microbes such as Acidithiobacillus ferrooxidans that can bind and recover metals, bypassing the need for high temperatures and toxic chemicals [ 87 – 90 ]. This emerging technology offers an eco-friendly approach to recycling but still requires extensive research and development. Additionally, a new infrastructure must be put into place, supporting millions of electric cars at the same time. To that point, a combination of synthetic and biofuels in synergy with electric cars might be an optimal solution for the years to come, partially substituting fossil fuels, thereby drastically reducing CO 2 output of transportation.
The transport sector, specifically, results in 17% of emissions. Adapted from Ritchie and colleagues (2020), Carbon Leadership Forum 2020 [ 85 , 86 ].
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EU policy recommendations
In order to promote the use of clean and sustainable energy at the industrial, retail, and consumer level, a cohesive framework of policies is imperative. The European Commission and European Environment Agency (EEA) have cooperated with the International Renewable Energy Agency (IRENA) and the Intergovernmental Panel on Climate Change (IPCC) in leading the efforts for clean energy transition through a number of directives and legislations since the 1990s [ 91 – 94 ]. These efforts manifest as a commitment by EU countries to lower GHG emissions and increase the use of renewable energy. Most notable is the Renewable Energy Directive (RED), which came into force in 2009. Through this directive, EU countries set targets for renewable energy consumption, including a subtarget mandating 10% of energy used in transport to be produced from renewables. It is noteworthy that the deployment of renewable energy has continuously grown, exceeding 22% in 2020 [ 92 ]. The legislation also mandates GHG reduction targets for fuel suppliers, requiring a reduction in GHG intensity of the fuel mix by 6% in 2020 [ 92 ]. In 2018, the commission revised the legislative proposal and the European Parliament and the EU Council proposed amendments as RED II. Therewith, the EU aims to increase the share of renewable energy to 32% and in transport to at least 14%, including a minimum share of 3.5% of advanced biofuels (second- and third-generation biofuels). The latter streamlines waste residues, such as agricultural waste (e.g., straw), and also encompasses renewable electricity in road and rail transport [ 95 ].
At present, the industrial biofuel production is dominated by first- and second-generation processes, respectively. Nevertheless, RED II and indirect land use change (ILUC) proposals have initiated the gradual shift toward second- and third-generation processes, which are associated with significant changes in feedstock supply and logistics, as well as technology deployment (e.g., market penetration of advanced biofuels). ILUC qualifies first-generation biofuels based on the unintended consequences of releasing carbon emissions as a result of land use changes [ 96 , 97 ]. While technical process development for third- and fourth-generation biofuels is advancing rapidly in academic and start-up settings, large-scale industrial implementation remains lagging. This indicates a profound gap in transferring technologies from a pilot scale (TRL 5) to an industrial scale (TRL 8). To that end, clear and implementable criteria remain to be addressed by legislators for industrial technology transition toward advanced biofuels with a notable climate impact. Table 2 summarizes our policy recommendations aimed at advancing biofuels implementation as well as their respective expected results and acting entity.
https://doi.org/10.1371/journal.pbio.3002063.t002
First and foremost, legislators need to create stable policies and regulatory frameworks based on measurable cradle-to-cradle sustainability performance indicators. In the past, one of the greatest barriers for industry to adopt new biofuel technologies, at least in the EU, was the constantly changing regulatory and provisions framework, which ultimately led to waves of market and company consolidation for first-generation fuels such as crop-based biodiesel, corn and sugar beet-based bioethanol, and, more recently, corn-based biogas products. Therefore, it is of the utmost importance that policy makers provide clearly formulated, long-term stable policies, provisions, and regulatory frameworks to allow industrial transition to advanced biofuel technologies with clear climate impact.
With respect to sustainability, measurable criteria can be categorized as agriculture biomass, forest biomass with respect to biodiversity, and carbon stocks and emissions. Biofuel ILUC factors could be included in the biannual reports of fuel suppliers and EU countries. Accordingly, biofuel produced from palm oil and soy should carry a high ILUC factor and phasing out these feedstocks could be achieved by encouraging the diversification of feedstock. Reports estimate that 130,000 to 210,000 hectares of deforestation, which has detrimental effect on biodiversity and soil quality, could be avoided by limiting the demand of EU countries for palm oil biofuels [ 98 ]. Land requirement and fresh water use, carbon trading, and carbon offsets should also be factored in upcoming legislations. The criteria should also include GHG emissions that take the levels of methane, nitric oxides, and sulfur oxides into account in addition to levels of CO 2 . Legislation criteria should also take into consideration end-use performance, whereby industry sector, energy efficiency, and socioeconomic impact could represent qualifying measures. Risk determination and possible exceptions could be evaluated for specific industries, such as security and electricity. With respect to energy efficiency, it should be considered that distinct biofuels differ in their output. For example, ethanol yields 25% more energy than that invested in its production, while biodiesel yields 93% more [ 99 ]. To that end, performance-based renewable energy policies are needed. Finally, a reliable system that verifies compliance and reporting is eminent to putting these proposals into practice. In that respect, a mass balance system that observes the global carbon inventory and defines optimal distribution of energy profiles (first to fourth generation) and mixtures (e.g., E10 petrol/ethanol) to ensure minimal climate impact is in order. This system could integrate a range of parameters, including flexible distribution channels, demand management, storage, and price signals in real time [ 97 , 100 ]. Independent auditing services could further ensure compliance, which could also be extended to trading partners of the EU countries at a later stage.
As the implementation of industrial biofuel production sites are associated with immense capital investments, it is crucial to shed light on the financial aspect linked to these policies, primarily, multilevel incentives schemes, investment risk reduction, and infrastructure and logistics. On an EU level, specific funding mechanisms such as European Innovation Council (EIC) pathfinder, EIC Transition, and EIC Accelerator that aim to enable and accelerate the scaling trajectory of new technologies toward market entry already exist. While this is an initial step toward implementing new biofuel technologies, these measures do not translate into national actions and legislation on a member state level, which impedes the regional mobilization of capital, leading to a slow uptake and implementation of new technologies. Hence, a significant step toward rapid technology adoption and implementation would be the regional implementation of funding and capital mobilization as already practiced on the EU level.
An integral element in promoting advanced biofuels could be incentivizing biofuel processes that show favorable sets of sustainability parameters and end-use performance by a higher cost of CO 2 certificates, which realistically should be in the order of 500 to 1,000 Euros/ton CO 2 . Consolidated long-term measures would also provide companies and investors with valuable tools to calculate return of investment and hence de-risk decision-making for iterative technology transition. To enable more efficient technology transfer from academia toward industrial technology deployment, additional factors need to be considered. To that end, academic projects should receive sequential, stage-gated extended funding periods of 4 to 8 years that commonly go beyond a single governmental administration period. This would allow ideas to be developed toward a proof of concept stage, where they can be translated to spin-outs or industry partners. Governments should incentivize start-up formation derived from academic units using focused funding measures, such as the EXIST funding program in Germany [ 101 ]. As technology development from proof of concept (TRL 2 to 4) in academic settings to pilot plant level often requires time periods exceeding 5 to 7 years, synergistic midterm private funding resources also have to be mobilized. To that end, technology familiarity, better understanding of time frames for solid technology development, and proper risk assessment are essential for private capital investors. In order to motivate private capital in the EU to accept development risks and extended time frames for return of investment in biofuel start-up companies, governments could implement tax write-offs for spent risk capital. This legislatively guided de-risking of capital investment into new technologies is already implemented in the United States of America and the United Kingdom, as well as in other, less compliance-driven, financial markets. Hence, the EU has to rapidly implement such legislative tax reliefs to secure innovation on the biofuels and other innovation and sustainability-driven sectors for added economic value and a vibrant job sector.
Capital is also short at the infrastructure and logistics level. Investments are required to construct dedicated pilot plants that allow industrial scale validation and optimization of new technologies, independent of any large-scale industrial partner. In that respect, multiple regionally decentralized pilot plants could provide dedicated instrumental parks that house state of the art fermentation and downstream processing equipment. In the case of gas fermentation, these parks could be associated with significant security measures and demand special regulatory approval and regular inspection. Accordingly, construction and operation by large national research organizations, such as Fraunhofer institutions in Germany, or private–public partnerships is recommended. Governmentally driven funding actions that enable access and use of these pilot plant facilities by innovators in the biofuels sector could further accelerate industrial deployment and market entry. In parallel to technology market readiness, the implementation of biofuels in industrial processes requires a secured feedstock supply.
Contrary to Nordic countries that are the forefront of advanced biofuel processes development, most industrialized countries in the EU with a high population density do not have sufficient land or biomass availability for large-scale biofuel production [ 100 ]. Hence, the location and feedstock supply require strategic positioning. Two routes for biofuels production are viable in the EU: a large production plant located in a region with abundant, long-term feedstock/biomass supply or secured trade routes; or a network of smaller, decentralized production facilities. In the latter case, a farm-integrated production facility with secured access to local residue streams can be envisioned. To optimize the economics of the production facilities, its location should be leveraged with maximal carbon credits in order to meet fuel market prices. To make an informed decision on the location and mode of production, a global carbon inventory map would be extremely beneficial. While we have a good overview of regional carbon emissions, there is little information on correlative carbon storage, which is mostly limited to terrestrial biomass. To that end, other carbon storage mechanisms should be considered, such as existing geological carbon (CO 2 ) capture activities and marine biomass. Considering that 68% of the world population is projected to live in urban areas by 2050, it is sensible to consider urban waste streams, such as sewage sludge and food waste, as yet underutilized biomass feedstocks for biofuel production processes [ 102 ]. More generally, a map of the carbon flux resolved on a country-specific level would enable a more informed decision on the selection of process feedstock (biomass residues/CO 2 ) and trading partners that could secure operation of large-scale production facilities for third- and fourth-generation biofuels. Currently, the major trading partners of the EU are Argentina, Brazil, USA, Indonesia, and Malaysia [ 97 ]. These trading practices do not ensure level field sustainability over the long term. To that end, future trading legislation should consider balanced trade between the global North and global South to ensure long-term beneficial socioeconomic impact on the stability and sustainability of feedstock and biofuel production.
Conclusions
In this Essay, we laid out the reasoning for biofuel production as immediate and long-term measures to limit and eliminate energy and mobility-related GHG emissions. In that regard, biofuels will not be the only solution but an essential building block in a network with other physical (i.e., wind power, photovoltaic systems [ 103 – 105 ]) and chemical technologies (i.e., Sabatier process, Power to X [ 106 , 107 ]) that together can provide carbon neutral or even carbon negative energy and mobility solutions. In regard to transportation, biofuels should act in synergy with other technologies, such as electrified vehicles. In addition to biofuel manufacturing, similar processes could also be implemented in other applications. Here, algal and yeast oil can be transformed into building materials such as carbon fibers and cement additives. Via these routes, atmospheric CO 2 can be absorbed from the environment and stored for very long periods of time. Such technologies could complement materials derived from fossil fuels or that generate large amounts of CO 2 during the manufacturing process (e.g., steel, aluminum and concrete) [ 108 ].
We are convinced that, in the last decades, mankind has been generally too hesitant to adopt climate-centered technologies, which has put the world on a perilous pathway toward catastrophic climate change [ 109 – 111 ]. The destructive outcomes of this scenario have been documented in the scientific literature and are subject to numerous high level reports [ 112 – 117 ].
As time for action is already overdue, it is essential to act now by implementing the tools and technologies we have at hand at the present time. It is our opinion, that the only path to enable climate effective energy security and mobility is to deploy available technologies at a global scale right now. The global implementation of large-scale production infrastructure for sustainable (bio)technologies to kick-start production of renewable energy carriers and sustainable commodities is imperative in this timely development scenario. Once production with a base process has commenced, these processes can be iteratively refined or modulated at scale to evolve toward the next technology generation. This approach demands close, long-term academic and industry partnerships.
This fundamental transition toward sustainable bio-based technologies will require long-sighted, fact-driven legislative guidance and immense capital investments across the private and governmental sectors. However, it will be the only route to limit climate change effects and provide a livelihood for future societies.
With respect to governments, this means that neither ideology nor demagogically driven decision-making will protect any society from the effects of climate change. There are just no simple answers to complex, global problems. What is needed are global governmental alliances that make technocratically oriented long-sighted decisions, aiming for definitively set climate-centered outcomes even if the communication of the measures that have to be taken may not be popular on first sight.
Even outside the scientific communities, people are ready to accept change of the status quo in order to curb climate change effects and transition to a sustainable society. The question remains if the global political elites are ready to communicate and implement this change. Time is running out to maintain the global ecosystems as we know it.
Acknowledgments
The authors dedicate this manuscript to Dr. Christian Patermann (former EU Program Director Biotechnology, Agriculture, and Food) and Dr. Günther von Au (Chairman of the Board of Directors of Clariant AG), each being outstanding political and industrial visionaries, influencers, and decision-makers in the field of sustainable (bio)technologies and the bioeconomy, respectively.
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- Published: 25 June 2021
Microbial production of advanced biofuels
- Jay Keasling 1 , 2 , 3 , 4 , 5 , 6 ,
- Hector Garcia Martin ORCID: orcid.org/0000-0002-4556-9685 1 , 4 , 7 , 8 , 9 ,
- Taek Soon Lee 1 , 4 ,
- Aindrila Mukhopadhyay ORCID: orcid.org/0000-0002-6513-7425 1 , 4 , 9 ,
- Steven W. Singer 1 , 4 &
- Eric Sundstrom 4 , 10
Nature Reviews Microbiology volume 19 , pages 701–715 ( 2021 ) Cite this article
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- Metabolic engineering
Concerns over climate change have necessitated a rethinking of our transportation infrastructure. One possible alternative to carbon-polluting fossil fuels is biofuels produced by engineered microorganisms that use a renewable carbon source. Two biofuels, ethanol and biodiesel, have made inroads in displacing petroleum-based fuels, but their uptake has been limited by the amounts that can be used in conventional engines and by their cost. Advanced biofuels that mimic petroleum-based fuels are not limited by the amounts that can be used in existing transportation infrastructure but have had limited uptake due to costs. In this Review, we discuss engineering metabolic pathways to produce advanced biofuels, challenges with substrate and product toxicity with regard to host microorganisms and methods to engineer tolerance, and the use of functional genomics and machine learning approaches to produce advanced biofuels and prospects for reducing their costs.
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Acknowledgements
The authors thank C. Scown (Lawrence Berkeley National Laboratory) for helpful discussions on life cycle and technoeconomic analyses of biofuel production. This work was performed as part of the US Department of Energy (DOE) Joint BioEnergy Institute ( https://www.jbei.org ) supported by the DOE, Office of Science, Office of Biological and Environmental Research, and by the DOE, Energy Efficiency and Renewable Energy, Bioenergy Technologies Office, and as part of the Co-Optimization of Fuels & Engines project sponsored by the DOE, Office of Energy Efficiency and Renewable Energy, Bioenergy Technologies Office and Vehicle Technologies Office, under contract DEAC02-05CH11231 between the DOE and Lawrence Berkeley National Laboratory. The views and opinions of the authors expressed herein do not necessarily state or reflect those of the US Government or any agency thereof. Neither the US Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights. The US Government retains and the publisher, by accepting the article for publication, acknowledges that the US Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of the manuscript, or allow others to do so, for US Government purposes. The DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ).
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One-carbon microbial substrates, including CO 2 , CH 4 , CO, HCO 2 − and CH 3 OH.
A mixture of CO, CO 2 and H 2 .
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Petrol containing 10% ethanol by volume.
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Biofuel research: perceptions of power and transition
- Lena Partzsch 1
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Whether biofuels represent a sustainable innovation, a creative alternative, or a gold rush, very much depends on our perception of power and change with regard to sustainability. This article provides an overview of existing understandings of power in the research on biofuels, including positive perceptions that often lead to more optimistic evaluations of biofuels. It exposes the diversity with which one can understand power through three ideal type concepts: “power with,” “power to,” and “power over”. Integrating these concepts in one power framework allows for examining how the three dimensions interrelate with each other and developing the contours of a power lens on biofuel governance and research. With the 2007–2008 food price crisis, critics re-politicized the governance of biofuels. Several farmer associations have completely turned against biofuels. The article argues that this rejection of biofuels is due to a limited perception of power as a coercion and manipulation (power over). While the current governance of biofuels basically reproduces systems and positions, we should start to more seriously and intensively ask questions of where, when, and how the governance of biofuels may also allow for “green” resistance (power to) and collective empowerment (power with).
Introduction
Whether biofuels represent a sustainable innovation, a creative alternative or a gold rush [ 1 ], very much depends on our perception of power and change with regard to sustainability. This leads to the challenge of how to conceptualize these understandings. I gather diverse perceptions of power and illustrate them for biofuel research. The aim is to initiate a broader, more comprehensive debate across ontological and epistemological differences in this field of research. To begin the discussion, I introduce key components of the debate by identifying different perceptions of power that are common to research on biofuels along three ideal type conceptions:
Power with means collective empowerment through convincing and learning with and from each other. It refers to processes of developing shared values, finding common ground, and generating collective strengths [ 2 ]. Based on this understanding of power, biofuels can potentially be a sustainable innovation that serves the common good (climate protection, energy security, regional development, etc.) (e.g., [ 3 , 4 ]).
Power to corresponds to the ability of agents “to get things done” [ 5 ]. While Pitkin [ 6 ] defines power to as non-relational, Barnett and Duvall [ 7 ] define power to as tied to social relations of constitution that define who the actors are, along with their capacities and practices. Footnote 1 Scholars, who take a perspective of power to, may highlight the agency of producing biofuels as a creative alternative in hitherto fossil fuel-dependent societies (e.g., [ 8 , 9 ]).
Power over describes the direct and indirect ability of powerful actors, structures, and discourses to influence the actions and even the thoughts of others. It is based on power concepts by Dahl [ 10 ], Bachrach and Baratz [ 11 ], and Lukes [ 12 ], among others. I also discuss concepts of discursive power under this category (e.g., [ 13 , 14 ]), while I am aware that these concepts partly fall under the category of power to [ 7 ]. From a perspective of power over, biofuels can be seen as a gold rush: While everybody expected sudden wealth in this new field, there are very few winners and many losers (e.g. [ 15 , 16 ]).
I chose this tripartite approach as a framework for my article, because it is most comprehensive and makes an extension of the power discussion on biofuels possible. At the same time, the framework allows for the discussion of the well-known grouping of the four “faces of power” under the category of power over [ 17 , 18 ]. I will argue that in the research on biofuels, the understandings of power as power with and power to tend to prevail, even when they are not made explicit. This means that scholars have overemphasized the potential of biofuels as a creative alternative to fossil fuels and sustainable innovation for rural development. Concepts of power over have only more recently been applied, specifically since research has started to explicitly issue power. This has, in particular, been used to explain why any process of governing biofuels (biofuel governance) did not lead to urgent sustainability transitions, and why the biofuel boom should rather be seen as a gold rush. Scholars have demonstrated that the development of biofuels markets benefitted large companies and conglomerates [ 19 ]. Critical and post-structuralist perspectives have helped to understand this development by exploring structures and discourses favoring them [ 20 ]. Scholars have used Foucault’s concepts to outline how scientific knowledge practices render the very essence of problems (and solutions) raised on the biofuel agenda [ 21 , 22 ].
This article involves first of all implicit and explicit understandings of power (how do biofuel researchers think and talk about power?). These understandings are expressed in empirical research, as I will demonstrate below, and they hence also allow for an illustration of the practice of biofuel governance (how is power exercised in and through biofuel governance?). This makes the article also relevant for political practice. We should understand, not only in theoretical but also in practical terms, how we effectuate or prevent changes towards a more sustainable supply of energy and transport fuel. As in analytical heuristics, it is not possible to offhand separate power with , power to , and power over in empirical research. These categories shine multiple lights on different aspects of the same empirical phenomena. In practice, these forms of power exercise are mostly interrelated. My less concern is to weigh and compare the pros and cons of each perspective, but rather to outline an agenda for a multidimensional analysis of all three mechanisms of power and their interrelations.
In order to get the full picture of how change happens, we should understand how different perspectives add on to each other (besides overlaps and contradictions). To do this, I will begin by describing each perspective in itself. Based on a survey on biofuel research, I will give references for each perspective. These references are only illustrative. Then, I will exemplify the interrelations between each of these perspectives with respect to biofuel research. I explain how power imbalances can affect processes of power with and power to . Again, scholars have demonstrated how large conglomerates have manipulated biofuel governance in their favor, and why therefore the biofuels boom should be considered as a gold rush. However, I argue that interrelations may also work the other way around, and this is particularly relevant to the main argument of this article. Biofuels as a creative alternative and a sustainable innovation may also provoke changes in existing relations of power over and contribute to address asymmetries and inequalities in agrifood and transport systems. We need a multidimensional power approach to explore these interrelations.
Biofuel: sustainable innovation (power with)
Research on biofuel governance and other studies in the field of sustainability are most often based on a positive perception of power in the sense of power with . Power with is a term that refers to processes of developing shared values, finding common ground, and generating collective strengths [ 2 ]. This conception does not necessarily refer to the diffusion of already existing (predefined) norms. Rather, power with implies learning processes that allow actors to question self-perceptions and to actively build up a new awareness of individuals or groups [ 23 , 24 ]. In this vein, with regard to biofuels, scholars have assumed that collective empowerment and solidarity are possible and that biofuel technologies as a “sustainable innovation” can pave the way to post-carbon societies [ 25 , 26 ].
Power with is often linked to Arendt’s definition of power [ 27 ]. Footnote 2 According to Arendt, power always refers to a group or to a collective of individuals:
Power corresponds to the human ability not just to act but to act in concert. Power is never the property of an individual; it belongs to a group and remains in existence only so long as the group keeps together. When we say of somebody that he is ‘in power’ we actually refer to his being empowered by a certain number of people to act in their name ([ 28 ]: 44). Footnote 3
Research on environmental leadership (e.g., [ 29 ]) in pioneer countries, such as Germany and France in the biofuel sector [ 3 , 30 ], most obviously reflects such an understanding of power. Leaders or pioneers are empowered to act in the name of others from this perspective (while they dominate others from a perspective of power over , see below). In this sense, (Young [ 31 ]: 285) defines leadership in the interest of common welfare:
Leadership (…) refers to the actions of individuals who endeavor to solve or circumvent the collective action problems that plague the efforts of parties seeking to reap joint gains in processes of institutional bargaining.
Leaders and pioneers do not enforce their own interests against or over others; rather they seek “to reap joint gains” of environmentalism. Environmental leadership studies, based on such an understanding of power, usually follow the discourse of Ecological Modernization that highlights flexible and cost-efficient problem solving. Ecological modernization outlines a win-win storyline of environmental protection that benefits green (biofuel) business as much as the environment [ 32 , 33 ]. From this perspective, those who are neither leaders nor pioneers are considered free-riders or laggards , rather than subordinates. Non-leaders also benefit, at least in the long run, from power (with), since biofuels are expected to tackle common problems, such as climate change, enhance energy security, and to contribute to regional development [ 3 , 34 ]. Policies promoting biofuels are hence per se seen to be desirable since, from this perspective, they serve everybody’s interest.
Scholars have extensively analyzed the emergence, diffusion, efficiency, and effectiveness of policies promoting biofuels, with the (at least implicit) aim to foster their adoption and implementation [ 30 , 35 ]. In this context, policy learning and experiments have been gaining momentum [ 9 , 26 ]. Deliberative processes, including third-party certification schemes, were initiated and observed with the aim to introduce sustainable biofuel production schemes that would integrate those formerly excluded stakeholders with new technology; in everyday practice, every actor in the field would then become a winner [ 4 , 36 ].
Scholars who share this perspective of power as power with do not think in dichotomies such as winners - losers or good-bad . Instead, they understand power (or similar concepts, such as leadership) as serving the common good (climate protection, energy security, and sustainability). As there are no subordinates from this power perspective, no imperative follows to empower or to resist. The empowerment of non-leaders is not an issue because scholars assume that, in principle, they are also interested in developing sustainable innovations and that they likewise benefit from respective leadership efforts.
Biofuel: creative alternative and “green” resistance (power to)
While power with pertains to collective empowerment and solidarity, power to refers to single actors and separate groups, such as farmers, co-operatives, and individual processors who were initially key players in pioneering biofuel regions [ 19 ]. Accordingly, biofuels are often seen as an opportunity to empower green ideas and values. Pitkin [ 6 ] emphasizes how power can be non-relational, since an actor may have the power to accomplish something all by him- or herself. This understanding of power is related to the development of an individual identity; self-confidence and consciousness raising [ 23 ]. It is here where Nussbaum’s and Sen’s [ 37 ] capability approach comes in, which defines power as “a capability to act upon one’s environment” [ 38 ]. For example, an individual farmer can simply start to produce and use biomass-based fuels without any permission or interference from another actor, such as the petrol industry. However, constructivist research has demonstrated how every actor or group is defined through socially constituted relations that, at least indirectly, shape the actions of individuals [ 7 ]: only a farmer who receives knowledge about alternative technologies may effectively implement them.
Power to can be linked to Parsons’ definition of power as the ability “to get things done” [ 5 ]. It highlights a productive agency, especially in the cases where actors’ goals are opposed or resisted. Biofuel research by small farmers and rural communities is often based on this perception of power [ 9 , 39 ]. Scholars highlight the potential of biofuels for rural development by providing new markets for agricultural production. They assume that through the introduction of radically new technologies in niches, farmers are able to empower themselves in an attempt of an “agro-ecological revolution” [ 8 ]. They highlight the self-empowering agency of hitherto marginalized people to become “energy sheiks” [ 40 ], based on biomass production.
Scholars, who take a perspective of power to , focus on the productive agency of the biofuel sector. They are interested in the empowerment of alternative ideas and values which, in the case of biofuels, allow for transforming fossil fuel-dependent societies. These alternative agents criticize the practices or the authority of the dominant, carbon-intense system and refuse to reproduce their own positions in this system. Their non-conformism is perceived to serve the common good as they develop alternative technologies required by everyone in a world beyond petrol. From a perspective of power to and in difference to a perspective of power with , there are only a limited number of transformational agents: not everybody in the field is assumed to be a “winner” in the first place; there are only a few “energy sheiks”. However, scholars see an imperative to act based on normatively prior “green” values, for example, climate protection and sustainability (and everybody benefits from the realization of these values).
Biofuel: gold rush (power over)
Scholars who explicitly issue power in the context of biofuels usually perceive power as asymmetric. Biofuel governance is seen as a zero-sum game which produces winners and losers. From this perspective, powerful actors, structures, and discourses in the field of biofuel governance influence the actions and even the thoughts of others. In the following, I will illustrate this perspective, further differentiating the “four faces” of power over (see Table 1 ): visible , hidden , invisible , and unconscious power [ 2 , 41 ]. (the fourth dimension does not understand power as a zero-sum game and can also be added to power to , see the first footnote.)
In the first dimension, agents exercise visible power when they directly influence political decision-makers based on their material and ideational resources [ 42 ]. What is visible is not the power as such, but rather its physical means such as lobbying activities, party financing, and armed force. (Dahl [ 10 ]: 201) defines: “A has power over B to the extent that he can get B to do something that B would not otherwise do” (emphasis added). Any kind of state force implementing objectives of sustainability by top downregulation means exercising direct power. Non-state actors may also play a role in this game. Coase [ 43 ] explains this for business firms. Also when Pilgrim and Harvey [ 44 ] demonstrate how NGO lobbying significantly affected biofuel policy changes and sustainability regulation in the UK and in Europe, they assume that NGOs enforce their ideas against others in an arena of obviously competing demands.
The second dimension of hidden power refers to power not obviously opposed by anyone. Bachrach and Baratz [ 11 ] speak of “two faces of power” emphasizing that some issues never even make it onto the political agenda and are dismissed before observable negotiations start. For a long time, the EU issued biofuels only in the context of climate change, completely neglecting aspects of competing food demands and land use change in the Global South [ 45 , 46 ]. Scholars demonstrating such hidden aspects apply this second dimension of power over to analyze biofuel governance.
The traditional conception of structural (hidden) power in international relations aims to address the coercion resulting from the capital mobility of transnational corporations. Threats to shift investments abroad do not even need to be voiced in order to influence policies in their favor [ 42 , 47 ]. More recent studies point to the fact that businesses also exercise structural power by self-regulation and public-private partnerships; these types of governance allow business actors to actively set rules, for example, for the “sustainable” production of biofuels at the expense of state actors [ 42 , 48 ]. In addition, as public authorities have faced challenges in facilitating the implementation of their sustainability criteria outside their jurisdictions, the EU has started to use these private schemes to verify compliance with sustainability criteria in biofuel production outside its own territory [ 49 , 50 ]. As a result, following this perspective, power in the global political economy has been diffused, leaving biofuel conglomerates with considerable power over others [ 51 ].
Further, scholars are increasingly focusing on power relations linked to latent conflicts of interest. In the third dimension, invisible power comes to play as a result of norms and ideas [ 41 ]. Research analyzes discourses, communication practices, cultural values and institutions, which all work to shape relevant thoughts and actions [ 12 ]. With regard to biofuels, Munro [ 22 ] has shown how, in the United States, a powerful coalition of agricultural interests manipulated the governance of biofuels by linking it to public concerns about climate change and energy security. In consequence, corn biofuel received political support, tax reductions, and subsidies. Likewise, Puttkammer and Grethe [ 52 ] have found a coalition of biofuel advocates to dominate the public discourse in Germany, while scientists who doubted the efficiency of biofuels could not make their voice heard. The discourse only shifted with the 2007–2008 food price crisis when scholars demystified the “ethanol bubble” [ 53 ] and outlined potentially devastating implications for global poverty and food security. Experts, NGOs, and business actors who have challenged the sustainability of biofuels on many fronts began to be heard [ 20 , 22 ].
For the most part, these discourse scholars blame other scholars who apply a perspective of power with for neglecting and postponing important questions of social justice linked to biofuel production [ 21 , 54 ]. Win-win rhetoric is demonstrated to manifest global power asymmetries rather than to contribute to more ecology and fairness [ 22 , 53 ]. From this perspective, pioneers and leaders, whose role Young [ 31 ] and Bernard and Prieur [ 30 ], among others, consider to be positive, only serve dominant interests and prevent a more fundamental social transformation to sustainability. With reference to the International Political Economy, most scholars deny a simple confrontation of biofuel proponents (or pioneers) and opponents (or laggards). In this vein, Levidow [ 55 ] outlines how the EU can continue “its global plunder of resources” because it pursues global leadership for sustainable biofuels. Silva-Castaneda [ 56 ] demonstrates how, in Indonesia, some NGOs decided to participate in the Roundtable on Sustainable Palm Oil (RSPO), a certification process initiated by the WWF, among others. The local NGOs managed to include important clauses regarding indigenous and land rights in the RSPO standard. In practice, however, auditors rarely recognize as valid evidence the forms of proof put forward by local communities, and global conglomerates could even use the standards to increase their primacy vis-à-vis local farmers [ 56 ]. These examples reveal power over within multi-stakeholder processes.
Studies demonstrate that the expansion of biofuels in countries of the Global South was only possible through the partial neglect (simplification) of their cultural and ecological diversity [ 57 ]. Nygren [ 58 ] illustrates how leading retailers, in negotiation with environmental organizations, have guided consumers’ expectations of certified Southern forest products by building images of Southern community forest producers as authentic and exotic others . She concludes that certification as a market-based form of governance has only had a limited impact on altering the unequal relationship characteristic of global networks of production and consumption.
With reference to Foucault [ 13 ] and Bourdieu [ 59 ], we can capture links between knowledge, power, and politics in a fourth dimension of power over [ 17 ]. Critical and (post-) structuralist approaches understand power in a way that everything is socially constructed. Scholars analyze the normative impact on (supposed) losers, such as farmers in the Global South, as well as on (supposed) winners, such as major agribusiness actors. All actors work to mainly reproduce systems and positions [ 60 ]. With regard to biofuels, several studies have highlighted the central role of knowledge and framing [ 15 , 16 , 21 ]. Drawing on Foucault, Kuchler and Linnér [ 21 ] have analyzed the discursive practices of the three major international organizations focused on food and agriculture, energy, and climate with regard to biofuels over the last 20 years: the UN Food and Agriculture Organization (FAO), the International Energy Agency (IEA), and the Intergovernmental Panel on Climate Change (IPCC). They found that, in contrast to pro and contra accounts, the arguments of all three organizations reflected a policy consensus based on the mainstream notion of industrial agricultural production, promoting the intensification and expansion of rural production. The biofuel discourse has further constituted a concatenation of the three issues of agricultural production, energy security, and climate change mitigation. When the discourse shifted with the 2007–2008 food price crisis, all the three major organizations adapted to this shift [ 21 ]. Instead of exercising power over by manipulating discourses on biofuels according to specific pro or contra interests, the organizations were found to rather reproduce hegemonic discourses and their own positions.
The gold rush metaphor is used a lot to describe the situation of biofuels from a power over perspective [ 1 ]. Biofuel production, like gold mining, is unprofitable for most farmers, just like it was for diggers and mine owners. Both biofuel production and gold mining can in addition have very negative environmental effects. While, however, people are made to believe that everyone can become abundantly wealthy (“energy sheiks”), only some few investors make large fortunes. Applying discursive approaches of power over , we can argue that even such investors and major businesses are subject to and not only conscious manipulators of discourses of agricultural intensification and economic growth. The analysis of power over helps to understand why change to more sustainable transport and agricultural systems does not happen. However, as I argue in this article, it falls short on explaining when and why there also sometimes is disruptive change and empowerment.
Power to change: interrelations between power with, power to, and power over
While the perspectives of power with and power to (over-) emphasize the potential for change with regard to biofuels, scholars with understandings of power over often exaggerate their negative impacts. The tripartite framework allows for the combining of different analytical perspectives and to examine their interrelations. While the three categories are first of all analytical heuristics, they also stand for different mechanisms of the exercise of power (see Fig. 1 ). Power over affects what is considered a “sustainable innovation” and “creative alternative”. Research has demonstrated this. However, I argue that it is also possible the other way round: there are situations in which power with and power to can address power imbalances and prevent a situation in which there are only a few winners and many losers as a result of biofuel governance.
Agent-based power
As shown in Fig. 1 , besides considering material and ideational sources of power, we also need to consider different mechanisms of power (over/to/with), since they lead to different results of power (leading to a new distribution of sources in a circular process, see the arrow at the bottom of Fig. 1 ). Biofuels per se are neither a sustainable innovation, a creative alternative nor a gold rush. The three metaphors exemplify three different results of power: the exercise of power over leads to a gold rush situation. So, if scholars only ask for power over , they will always find winners and losers. By contrast, if we ask for the exercise of power to , we may find that biofuels are creative alternative. Finally, the exercise of power with can be exemplified by a case of finding an agreement on sustainability criteria of biofuel production. To demonstrate overlaps, especially, in terms of the results of power, I used dashed lines in Fig. 1 .
When, in the field of biofuels, scholars explicitly issue power, they generally use concepts of power over to explain why governance and research in this field have a blind spot for power asymmetries [ 49 , 53 ]. Biofuel opponents may have accomplished a shift in the biofuel discourse after the 2007–2008 food price crisis [ 20 , 22 ]. However, overriding power asymmetries have prevented a structural change in both the energy/transport and the agricultural sectors. The trend is now definitely towards large companies and conglomerates [ 49 , 50 ].
However, the fact that biofuels have caused no structural change and have disadvantaged rather than empowered small farmers in the Global South, does not mean that a structural change is impossible. What I want to argue in this article is that exercising consensual forms of power (power with) as well as self-empowerment and resistance (power to) can also eclipse and overcome power asymmetries (power over). Empirical research on deliberative processes suggests that communication and common action never happen among equals and that they are never free from any form of power over [ 36 , 61 ]. Hence, we need to understand power with as a form of exercising power, which is strategic (bargaining) as well as communicative (arguing). A crucial part of this process is the orientation of agents involved in processes of biofuel governance. If actors are open to changing their positions and developing shared understandings, transitions to sustainability can follow from dialogues [ 61 , 62 ].
Following this perspective, even if small farmers in the Global South have fewer capabilities compared to conglomerates from the EU and the United States, this does not mean that they have no possibility to act independently from them. For example, sugar is costly to establish, and thus is economically most efficient at large plantation scales. However, Jatropha can more readily be produced through outgrower schemes as it is less capital intensive [ 9 , 49 ]. While currently almost all bio-ethanol is produced from grain or sugarcane and therefore competes with food purposes, other efficient and economically viable technologies for ethanol production are available [ 63 ]. The production of perennial energy crops, such as grasses and trees, and crop residues, such as straw, are seen to require fewer inputs and less prime land [ 64 ].
Under specific conditions, empowerment is possible; processes of power with and power to can have a (positive) impact on unwanted relations of power over . For example, processes of stakeholder dialogue and certification demonstrate that an agreement beyond the lowest common denominator is possible. In addition, they can weaken the perceived legitimacy of powerful actors that are producing biofuels unsustainably. The critical discourse on biomass certification has issued consumers’ accountability for harmful social and environmental effects in countries of production [ 55 , 65 ]. When the legitimacy of unconditional import as well as of private certification schemes was put into question [ 50 ], transnational conglomerates lost ideational and material resources on which their power over others was based. In the agrifood sector, we can clearly see that certification has become a new normative obligation [ 66 ].
We can observe various kinds of empowerment and resistance related to biofuels. While Nygren [ 58 ] argues that certification schemes reproduce (inferior) positions of southern producers as authentic and exotic others, she does not completely deny that certification had a positive impact on altering asymmetries in global networks of production and consumption. Silva-Castaneda’s [ 56 ] study discloses new ways in which local communities can legally prove their land rights, for instance, by video documentation to replace missing formal documents or destructed land marks.
Scholars have described movements, such as Via Campesina, in terms of exercising power over and opposing transnational agriculture corporations [ 67 ]. In terms of reducing and overcoming power asymmetries, however, what is most striking is the fact that small farmers within this movement exercise power to by doing healthy and sustainable agriculture independently of the major agribusinesses to which, from a power over perspective, they would only be subordinated. At the same time, when producing organically, small farmers do not reproduce the system of industrial agricultural production (and their inferior positions within that system). So, their way of farming can be considered as a creative alternative and as a way of resistance. Moreover, within this movement of Via Campesina, despite widely different internal cultures, farmers also exercise power with by (re-) constituting a new shared peasant identity. From a perspective of power with, we can argue that, in the long run, everybody, even from outside this movement, may benefit and share norms and values developed here such as sustainability in farming. The movement delegitimizes the acquisition of land by established conglomerates (“land grabbing”), whose ideational sources of power shrink in consequence. The visible result is a new, more equal, and just distribution of (power) resources through land reforms.
Conclusions
This article should not only encourage a debate on power issues with regard to biofuels, but moreover, develop the debate more comprehensively. When political power has been analyzed in the context of biofuels, this has happened so far through using confrontational or structuralist and discursive approaches that are based on an understanding of power over . Respective scholars have accused other researchers of neglecting “real power concentrations” in the biofuels industries. Often quite rightly: biofuel research has neglected the limits of win-win for a very long time. Scholars have taken sides and normatively inflated their own pro biofuel position, while they have dispatched their adversaries as laggards with regard to the future of transport and agriculture. Of course, not every (supposedly) sustainable innovation is necessarily good in the sense that it is completely uncontroversial (even if there is no visible opposition as in the case of biofuels for a long time). In this context, the question of power essentially addresses the re-politicization of decisions perceived to be urgent and without alternative. With the 2007–2008’s shift in discourse, critics re-politicized the governance of biofuels. Several farmer associations have completely turned against biofuels. I argue that this rejection of biofuels is due to a limited perception of power as power over .
Why does it make sense to complement such a perception of power over ? Why does a multidimensional power framework make more sense? Naming different perspectives, as done here, with one and the same term—“power”—means, first, to put them on one normative level. Gold rush (power over) is a term with strongly negative connotations, on the one hand, and leads to normatively inflating sustainable innovations (power with) and creative resistance (power to), on the other. This is often unjustified because the exercise of power with and power to are not per se more legitimate forms of achieving social change. For example, preventing greenhouse gas emissions “from above” can be quite legitimate.
Secondly, as illustrated in this article, all three conceptions of power are already used in research on biofuels (although sometimes only implicitly; this should change). My hope is that this article addresses diverse communities and overcomes boundaries between them with this multidimensional power approach (in particular, between those who still celebrate biofuels as a “sustainable innovation” and those scholars who completely condemn them because of related power asymmetries). Especially those whose research is (implicitly) based on understandings of power as power with and power to could take stronger reference to researchers taking a critical viewpoint on their studies (power over)—in particular, through showing how consensual forms of power exercise (power with) and resistance and empowerment (power to) not only reproduce power asymmetries but also help overcome them. If we look at the gold rush metaphor from a perspective of power to , we may see that there is a lot of entrepreneurship involved in the discovery of gold deposits. From the perspective of power with , we may also see that people in the field of gold mining as well as of biofuel production find common ground among diverse interests and organize with each other.
Third, convincing and learning (power with) as well as creative ability (power to) and coercion and manipulation (power over) do not completely capture concrete change processes. The analytical categories applied in this paper help to cluster the various understandings of power in biofuel research, but they also reflect different mechanisms of power in reality. Power with perspectives focus on the benefits of biofuels (sustainable innovation); power to focuses on how new actors develop alternatives to fossil (and nuclear)-based economies; power over points to the limits of change because of the dominance of specific actors, structures, and discourses. The common terminology allows that the three perspectives on power are not considered as mutually exclusive (different interpretations of the same phenomenon), but as supplementary (different aspects of a change process). It becomes possible to examine their interrelations and their supplementary potential. With this article, I hope to have given an impetus for further research in this direction. A comprehensive analysis of power in diverse parts of biofuel research and governance is definitely a prerequisite for more seriously and intensively exploring questions of where, when, and how the governance of biofuels may also allow for “green” resistance and collective empowerment.
If actors create (reproduce) discourses and structures, I call this power to . Most constructivist studies however deal with identifying dominant (hegemonic) structures and discourses over others that are unconsciously reproduced, i.e., power over .
Power with is not identical to Arendt’s understanding of power or its empirical operationalization hardly accomplishes Arendt’s demands. So deliberative theories of democracy build upon her understanding of power without finding it comprehensively implemented in reality [ 61 , 68 , 69 ]. In difference to deliberative processes, power with encompasses communicative as well as common action.
An example, to which Arendt refers in a footnote to her definition of power, is the student protests at Berkeley and elsewhere at the end of the 1960s. She contrasts the power of the students—“obviously the strongest power on every campus simply because of the students’ superior number” ([ 28 ]: 44)—to the violence of the university authorities. An individual student leader ‘in power’ would speak on behalf of the movement.
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Partzsch, L. Biofuel research: perceptions of power and transition. Energ Sustain Soc 7 , 14 (2017). https://doi.org/10.1186/s13705-017-0116-1
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Latest development in microalgae-biofuel production with nano-additives
- Nazia Hossain ORCID: orcid.org/0000-0001-7925-0894 1 ,
- T. M. I. Mahlia 2 &
- R. Saidur 3 , 4
Biotechnology for Biofuels volume 12 , Article number: 125 ( 2019 ) Cite this article
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Microalgae have been experimented as a potential feedstock for biofuel generation in current era owing to its’ rich energy content, inflated growth rate, inexpensive culture approaches, the notable capacity of CO 2 fixation, and O 2 addition to the environment. Currently, research is ongoing towards the advancement of microalgal-biofuel technologies. The nano-additive application has been appeared as a prominent innovation to meet this phenomenon.
The main objective of this study was to delineate the synergistic impact of microalgal biofuel integrated with nano-additive applications. Numerous nano-additives such as nano-fibres, nano-particles, nano-tubes, nano-sheets, nano-droplets, and other nano-structures’ applications have been reviewed in this study to facilitate microalgae growth to biofuel utilization. The present paper was intended to comprehensively review the nano-particles preparing techniques for microalgae cultivation and harvesting, biofuel extraction, and application of microalgae-biofuel nano-particles blends. Prospects of solid nano-additives and nano-fluid applications in the future on microalgae production, microalgae biomass conversion to biofuels as well as enhancement of biofuel combustion for revolutionary advancement in biofuel technology have been demonstrated elaborately by this review. This study also highlighted the potential biofuels from microalgae, numerous technologies, and conversion processes. Along with that, the study recounted suitability of potential microalgae candidates with an integrated design generating value-added co-products besides biofuel production.
Conclusions
Nano-additive applications at different stages from microalgae culture to end-product utilization presented strong possibility in mercantile approach as well as positive impact on the environment along with valuable co-products generation into the near future.
Biofuel has caught substantial attention worldwide nowadays as an alternative fuel due to its capability to adapt with gasoline for a maximum 85% blend without any engine modification. Subsequently, the suitability of various candidates for biofuel is being continuously quested by the researchers and environmentalists [ 1 , 2 , 3 , 4 , 5 ]. In this recent era, one of the most sophisticated technologies, nano-technology integration with bioenergy application by the nano-energy sector has brought a revolutionary impact on biofuel conversion processes and enhancement of engine performances. Nano-technology is defined as designing a device or material in nano-scale (10 −9 m). To accelerate the biofuel yield and improve the efficiency of biofuel utilization in petrol and diesel, nano-technology has been initiated via nano-additives such as nano-magnets, nano-crystals, nano-fibres, nano-droplets, and others [ 6 , 7 , 8 ]. Figure 1 presents the perspectives of nano-additives on microalgae cultivation to microalgal-biofuel implementation.
Nano-additive applications for the enhancement of microalgae cultivation to biofuel implementation
On this eve of the quest for suitable biomass for biofuel, the concept of microalgae cultivation appeared to the spotlight for biofuel manufacturing due to several positive perspectives such as (i) they do not clash with human or animal food chains, (ii) very rich with carbohydrate, protein, and oil content, (iii) can grow in aqueous media such as wastewater, freshwater, saline water, and assimilate nutrients from brackish water, salt water, or highly polluted water, (iv) demand low water, (v) sustain capability to grow whole year naturally with sunlight presence, (vi) can be cultivated in the waste dump area, sea, ponds, rivers, industrial, and municipal waste drainage, wet bare lands especially in cold regions, (vii) develop sustainable O 2 generation system, and (viii) diminish CO 2 by up taking it for photosynthesis respiration [ 9 , 10 , 11 , 12 , 13 , 14 ]. In addition, microalgae contain very short harvesting life cycle and yield nascent biomass that drives higher productivity of the desired biofuel. Interestingly, microalgae carry a prodigious amount of carbohydrates, protein and lipid, the sole components of biofuel conversion [ 13 , 15 , 16 , 17 ]. Nano-technology applications have been implemented to biofuel industries, since the existing controversial approaches of traditional microalgae culture-biofuel production contain a number of limitations such as inconsistent industrial-scale microalgae production, high microalgae production and harvesting cost, energy consumption for biofuel production from microalgae, and the increase of greenhouse gas intensity in environmental [ 18 ]. Nano-technology applications can be entailed in different stages from microalgae cultivation to microalgae-biofuel application in fuel engines due to durability, recyclability, adsorption efficiency, catalytic performance, stability, crystallinity, economical advantage, high storage capacity, excellent biofuel yield, and environment-friendly characteristics. According to the previous studies, nano-technology application enhanced microalgae cultivation, the maximum yield of numerous microalgae biofuels as well as microalgae-biofuel implications in petrol and diesel engines. Various nano-materials, e.g., nano-fibres, nano-particles, nano-tubes, nano-sheets, and other nano-structures, have been investigated as effective nano-catalysts in direct and indirect approaches in biofuel (e.g., bioethanol, biodiesel, biomethane, and others) yield enhancement [ 19 , 20 , 21 , 22 ]. For instance, magnetic nano-particles were used as a carrier for enzyme immobilization for bioethanol and biodiesel generation effectively. Owing to high coercivity and powerful paramagnetic characteristics, magnetic nano-particles were also preferred for methanogenesis to produce biomethane [ 21 ].
To authors’ best knowledge, no review study has been performed on numerous biofuel productions from microalgae integrated with the nano-additive application so far. The closest review with this study was conducted on the bioenergy production from lignocellulosic biomass (agricultural residues), industrial waste (sludge) as well as algae (microalgae and macroalgae) with the nano-scale optimization which has merely emphasized on the mechanism of nano-particles, biomass characteristics, and nano-particle application on biomass growth [ 23 ]. Compared with that, the current review contextualized the numerous biofuel productions from pure microalgae and optimization with nano-additive application on biomass growth to end-product application. Therefore, the major objectives of this review work are (i) to determine the array of the techniques and methods associated with nano-particles incorporation with microalgae culture as well as microalgal biofuel, (ii) to demonstrate divergent nano-additive applications on microalgae cultivation, biomass conversion to biofuels, and biofuel combustion, (iii) to identify the potential sources of microalgae, especially the carbohydrate, protein, and lipid-enriched microalgae types for biofuel production and determine the possible microalgae biofuels, biomass conversion technologies, and processes to biofuels, and (iv) to assess the future prospects of the process development planning along with integrated design of some other value-added products besides biofuel.
General perspective of microalgae
Microalgae are referred as photosynthetically driven single or multi-cellular living being, the habitat of moist environment either on the solid mud or float on various water types, e.g., fresh water, marine water, wastewater with the presence of sunlight, or artificial light. The scientific consensus is that through photosynthesis respiration, they convert CO 2 to O 2 and generate large amounts of cellular energy content embedded with sugar, protein, and lipid [ 24 , 25 , 26 , 27 ].
Nowadays, industrialization and urbanization threaten the existing ecosystem severely by dumping heavy metal waste containing phosphorus, nitrogen, sulfur and others as well as exhaling high amount CO 2 to the free air. Another knocking threat to the energy sector is rapid depletion of fossil fuel worldwide due to excessive energy uses [ 28 , 29 , 30 ]. With this circumstance, microalgae cultivation in the wastewater, unused fresh, and saline water, drainage is considered as suitable scientific solution for green energy due to some favorable aspects such as multi-functionality, genuine conversion competency biologically and flexibility with growth system, wastewater accumulation, CO 2 sequestration, and large amount of carbohydrate–lipid–protein content. To note, carbohydrate–lipid–protein are the main components to generate divergent biofuels (e.g., bio-oil, biodiesel, biobutanol, and others) and biogas (e.g., bio-hydrogen) [ 31 , 32 ]. The cellular components of microalgae are composed of huge fraction of lipid, protein, and carbohydrates resulting in the driving factors of biofuel production. Table 1 presents some well-known potential microalgae candidates for biofuels. These species were extensively researched in the laboratory and large-scale applications so far. Type and description of these species have been tabulated to present a detailed view of selected species, suitable growth conditions (such as water type and region for cultivation), availability, and cellular specifications. Table 2 represents prime microalgae cellular component composition of several well-known microalgae species for biofuel production [ 24 , 33 , 34 ].
Biofuels from microalgae
Numerous biofuels, e.g., bioethanol, biodiesel, bio-oil, biomethane, bio-hydrogen, and others, have been extracted from microalgae [ 46 , 47 ]. Nano-particles’ incorporation with microalgae cultivation (e.g., cell suspension, cell separation, and cell harvesting), biofuel conversion technologies, and biofuel application have amplified the overall yield in every stage [ 22 ]. According to the previous studies, a very small amount of colloidal hydrous iron(III) oxide particles boosted almost 100% microalgae cell suspension; magnetic particles incorporated with aluminum sulfate were very effective for cell separation from the mixed culture of Anabaena and Aphanizomenon microalgae species; silver nano-particles application on Chlamydomonas reinhardtii and Cyanothece 51142 microalgae harvesting increased 30% higher biomass productivity; and calcium-oxide nano-particles escalated the large-scale biodiesel conversion yield up to 91% via catalytic transesterification [ 18 , 22 , 48 ]. This study summarized the overall microalgae cultivation integrated with nano-particles until biofuel production in Fig. 2 . Different biofuels from microalgae and conversion processes are diagrammed in Table 3 .
Process flow diagram of carbon capture, water treatment and biofuels production from microalgae incorporated with nano-particles [ 18 , 25 , 49 , 50 , 51 , 52 , 53 , 54 ]
Preparing techniques of nano-additives for microalgae biofuel
Magnetic nano-particle (NP) powder has been enumerated to the microalgae cell suspension in the photobioreactor cultivation process to flocculate cells for uniform distribution of nutrients and light all over the reactor. Immunomagnetic detection and modification of microalgae cell by NPs are another well-practiced method for cell suspension enhancement. Nano-liquid has been injected to the cell culture for microalgae harvesting and bio-separation through this technique. Silver nano-materials have also been implemented on the photobioreactor surface coating for higher light accessibility [ 22 ]. Along with microalgae culture and harvesting, sphere nano-particles have been enacted during hydrolysis, lipid extraction, transesterification, and biofuel purification from microalgae via irradiation and ultra-sonication methods and much higher biofuel yield have been obtained. Another established method of nano-materials application includes enzymatic nano-catalyst, lipase carrier. The reactant diffusion rate enhancement by the NPs to the active side of lipase has been determined by Eq. 1 [ 55 ]:
where R df = diffusion rate to the active sides of lipase and D = diffusion path diameter of reactant to the access of lipase active side.
NPs for biofuel doping can be formulated by either physical or chemical methods. For instance, plasma-arcing, sol–gel method has been presented as chemical method and ball mill process (agitation rate: 450 rpm) was presented as a physical method for NPs’ preparation in the previous studies [ 56 , 57 , 58 ]. Subsequently, NPs were doped with microalgal biofuel (e.g., microalgae oil, biodiesel, bioethanol, and others) with different doses (e.g., 25 ppm, 50 ppm, 100 ppm, and others) via ultra-sonication processing by the presence of magnetic stirrer and implemented on compression ignition (CI), direct ignition (DI) engines without any engine modification. NPs are dispersed in a base fuel and smoothen potential agglomerate into nano-scale due to its’ larger surface area and surface energy [ 58 , 59 , 60 , 61 ]. The ultra-sonication method was conducted with various parameters such as frequency (e.g., 20 kHz, 40 kHz, and 45 kHz), power (e.g., 120 W and 220 W), and time (30 min and 60 min) [ 60 , 62 , 63 ]. Cationic surfactants, e.g., tetra methyl ammonium hydroxide, cetyl trimethyl ammonium bromide, have been incorporated on the nano-particle surface for a negative-charge envelope formation to resist NPs’ sedimentation [ 56 , 64 ]. After biofuel-NPs’ doping, the NP-blended biofuel was preserved under the static condition to stabilize for fuel purpose [ 59 ]. Several potential NPs–microalgae-biofuel blends are tabulated in Table 4 . The morphology and crystalline phases after NP-doping were analysed through a scanning electron microscope and X-ray diffraction, respectively [ 61 ]. Botryococcus braunii oil was doped with almost 50 nm sized titanium dioxide (TiO 2 ) and silicon dioxide (SiO 2 ) incorporated with biodiesel (B20) of different doses for enhanced fuel efficiency in CI engine [ 60 ]. Caulerpa racemosa green algae biodiesel (B20) was doped with 50 nm sized zirconium dioxide (ZrO 2 ) by the different doses for CI engine [ 59 ].
Future applications of nano-additives for microalgae-biofuel
Nano-additive application on microalgae-biofuel enhancement has been categorized into several stages from raw material production to end-product implications. The stages are:
nano-additives for microalgae cultivation;
nano-additives for microalgae biomass conversion to biofuels;
nano-additives for microalgae-biofuel applications.
Nano-additives for microalgae cultivation
Improvement of the microalgae biomass productivity with the minimum area requirement is considered as the main purpose of nano-additive application in the microalgae culture. Nano-technology is being applied for enzyme immobilization, since nano-structures broaden the immobilization surface area causing high loading power of enzymes and stability of immobilized enzymes. Enzyme immobilization can be performed in different approaches such as electrospun nanofibers, covalently attached enzymes into nano-fibres, and enzyme aggregate coatings on nanofibers. The enzyme immobilization was investigated on various carbon nano-particles, e.g., graphene oxide (GO), multi-walled carbon nano-tubes (MWNTs), oxidized-MWNTs (O-MWNTs), and fullerene (C60). Among these nano-structures, O-MWNTs yielded the highest, and C60 yielded the lowest [ 21 , 22 ]. Nano-particles’ (NPs’) application was implemented on several microalgae species harvesting and yielded outstanding in each phase of the application. Application of nano-particles on microalgae harvesting claimed 20–30% microalgae production cost in large-scale application [ 22 ]. Table 5 presents the harvesting efficiency of several microalgae species cultivated with various nano-particles. Nano-particles also boosted the light conversion efficiency in photobioreactor (PBR) during the microalgae culture period. It is also worth mentioning that PBR is run by artificial light sources consuming additional energy and cost. However, during biomass growth, light sources do not reach in culture broth inadequately due to self-shading and biofilm formation on the PBR surface. To achieve desired illumination properties and photo-conversion efficiency in the PBR, various light-emitting diodes (LEDs) equipped with nano-materials fabrication are being implemented recently. Gallium aluminum arsenide (GAA)-fabricated LEDs have been experimented on laboratory scale algae culture so far. It was evident that the application of optical fibres in algal culture saves much energy, additional light cost, and increase efficiency [ 18 ]. Another latest development of nano-particle, integration of metallic nano-particles (MNPs) with localized surface plasmon resonance (LSPRs) amplifies the light scattering at certain wavelength [ 65 ]. An experimental study revealed that silver nano-particles’ (Ag-NPs’) suspension in plasmonic mini-PBRs backscatter blue light strongly. The blue light increased the photosynthetic efficiency significantly for green microalgae, Chlamydomonas reinhardtii, and blue–green microalgae, Cyanothece 51142, and 30% higher microalgae biomass have been obtained [ 48 ]. Nano-particles addition in microalgae cultivation can also improve the yield of the CO 2 absorption from the atmosphere and CO 2 sequestration that can boost the biomass growth. For instance, nano-bubbles in microalgae culture remained stable for a longer time. Nano-bubbles also floated algae biomass into the culture, ensured high mass transfer efficiency, and improved biomass density by sufficient accumulation of CO 2 , O 2 stripping, and minor buoyancy. Moreover, nano-bubbles suspended the biomass around airlift-loop bioreactor (ALB) and required less energy than micro-bubbles. Uniform nonporous membrane of ALB was also capable of producing 100 nm sized bubbles for this purpose [ 18 , 66 , 67 ]. The previous studies also delineated that nano-additives played a significant role in flocculation and separation process before biofuel production besides microalgae harvesting [ 22 ].
Nano-additives for microalgae biomass conversion to biofuels
Among microalgae biofuel, biodiesel has been appeared as the most popular and commercial biofuel in the mobile fuel market. For the case of biodiesel production, applications of acidic and basic nano-catalyst spheres can substitute the chemical compounds such as sodium methoxide by reacting with the free fatty acids and oils. Additional advantages of these nano-catalysts are recyclability and positive economical impact. Moreover, reactions can take place with low temperature and pressure as well as this approach reduces the contaminant release to the environment borne by sodium methoxide [ 6 ]. An industrial biodiesel study demonstrated that commercial CaO-NPs presented 91% biodiesel conversion efficiency during scaled-up catalytic transesterification [ 18 ]. Experimental study of microalgae cultivation with spherical nano-particles composed with sand (silica) and calcium compounds revealed that microalgae cellular growth increased drastically without harming harvesting as well as biofuel production from vegetable oil. The best way to address this issue was described as one of the major driving factors for commercial biofuel, biofuel production cost dropped effectively [ 6 , 7 , 8 , 68 ]. The experimental study mentioned that mesoporous silica nano-catalyst, Ti-loaded SBA-15 presented ten times higher free fatty acids (FFA) and water tolerance level than any other catalysts for biodiesel production from vegetable oil as well as this nano-catalyst performed three times better than other effective nano-catalysts titanium silicalite-1 (TS-1) and titanium dioxide silicate (TiO 2 -S) [ 69 ].
Moreover, Ti-loaded Santa Barbara Amorphous-15 (SBA-15) nano-catalyst application reduced the chemical (alkaline catalyst, NaOH) cost of transesterification process for biodiesel production by recycling the nano-catalyst as well as this process is more environment-friendly [ 6 , 69 ]. On the other hand, sulfate incorporated Ti-SBA-15 also performed as biocatalyst to convert vegetable oil to 100% esterified bio-lubricant. In consequences, this nano-particle can be expected to produce bio-lubricant from bio-oil of microalgae [ 70 ]. Other study showed that Niobia (N 2 O 5 ) incorporated with SBA-15 application on biodiesel production from biomass through esterification presented a significant scenario for microalgae-biodiesel yield [ 71 ]. Another study delineated that the enzyme extracted from Pseudomonas cepacia conjuncts with the nano-particles such as polyacrylonitrile (PAN) nanofibre, Fe 3 O 4, and nanoporous gold; silica nano-particles with lipase enzyme from Rhizopus miehei ; ferric silica and magnetic nano-particles with lipase from Burkholderia sp., polyacrylonitrile nano-fibre bound with lipase from Thermomyces lanuginosa has performed very effectively to produce biodiesel from various bio-oil by the transesterification process [ 7 ]. Furthermore, nano-magnetic biocatalyst of KF/CaO–Fe 3 O 4 , Li(lithium)-doped CaO, Fe 2 O 3 –CaO, sulfate (SO 4 − ) incorporated Zi (zirconium), sodium titanate and carbon-based nano-tubes and nano-particles reached up to 95% or above biodiesel yield from diverse types of biomass and biodegradable waste [ 7 , 72 ]. Besides enhancement of biodiesel-yield efficiency, a type of NP, zeolite (an alumina silicate mineral), has been used as commercial absorbent during the transesterification process. Zeolites absorbed the undesirable moisture content (4–6%) and produced pure glycerine as co-product besides biodiesel. Mesoporous nano-particles also presented a vital capability for continuous microalgal-biofuel generation from biomass without cell lysis. Zeolites also removed lipids from the microalgae cell membrane [ 18 , 73 ]. Table 6 presented the applications of nano-additives for biodiesel-yield enhancements during microalgae to biofuel conversion, suitable conversion processes, and efficiencies.
Nano-particles were efficiently capable to perform as immobilizing beds for valuable enzymes due to their large surface area-to-volume ratio. This capability of NPs broke down the long chains of complex sugar of microalgae, converted it to simple sugar, and consequently turned into bioethanol via the fermentation process. Due to the large surface area, the interaction between the surface of the nano-particles and fuel surrounded by them achieved adequate stability to overcome density variations. Nano-particles prepared by carbon nano-tubes doped with iron-oxide nano-particles presented excellent biocatalytic efficiency in a bioreactor, recyclable option enzyme applications, less capital cost as well as better enzyme loading for this purpose [ 6 , 7 , 74 ]. A catalytic study mentioned that mesoporous niobium oxide (N 2 O 5 ) application on complex sugar (sucrose) possessed both Lewis acid (LA) and Bronsted acid (BA) sites to convert fructose to 5-hydroxymethylfurfural (HMF) with the highest yield so far. The synergistic catalytic effect from a large amount of both LA and BA acid site quantities and surface areas played a positive impact on the reaction rate with a few times faster conversions [ 75 ]. Functionalised multiwall carbon-nano-tube (MWCNT) immobilization presented more than 55% initial activity of microalgal hydrolysis for Candida Antarctica. Nano-catalysts such as cobalt–molybdenum fabricated with Si/Al have been experimented on Botryococcus braunii and presented stable hydrocarbons. Another nano-catalyst, mobil composition of matter No. 41 (MCM-41), mesoporous material effectively reduced oxygenated fractions of bio-oil through catalytic pyrolysis [ 18 ].
Nano-catalysts can synthesize biomethane produced from microalgae from wastewater into pure hydrogen and carbon content. In a further step, this methane can produce biogas through anaerobic digestion. Biogas could be used as raw material of bio-fuelled electricity generation further. The elemental carbon can also be utilized as pure nano-graphite for the applications on batteries, aerospace, automobiles, and others [ 6 ]. The latest development conducted by quantum sphere on marine microalgae species evinced biogasification from wet microalgae biomass by metal nano-catalysts [ 18 ]. Besides that, nano-particles such as TiO 2 , CeO 2 were manifested to improve 10–11% of the biogas yield from wastewater treatment. Therefore, these nano-particles can be projected further for the biomethane production from microalgae grown in wastewater [ 7 ]. Apart from that, nano-substances with SiO 2 , nano-particles of platinum (Pt), nickel (Ni), cobalt (Co), and iron (Fe) can increase methane production from biomass up to 70%. Nano-fly ash and nano-bottom ash were proved to increase biomethane yield up to 3.5 times more. Nano-metal oxides, e.g., MgO, CaO, and SrO, nano-materials such as silica, single-walled nano-tubes of carbon-based materials, nano-clay, and nano-zero valence metal applications in biodiesel, bio-hydrogen, and biomethane production from microalgae and other biomass presented outstanding yield. These nano-particles can be projected for large-scale microalgal-biofuel production in the future to obtain revolutionary yield [ 7 , 8 ]. In addition, nano-hybrid catalysts are being commercialized as emulsion stabilizers in industrial applications. For instance, quaternary ammonium salts have been documented as an emulsifying surfactant for separation, extraction, isolation, and purification of biofuels. Carbon nano-tubes with silica fusion, SiO 2 –MgO nanohybrids have been performed as stabilizers on bio-oil in water emulsion due to its inherent hydrophobicity and resulted in full conversion in different emulsion phases [ 18 ].
Nano-additives for microalgae-biofuel applications
Solid nano-particles, nano-fluids, or nano-droplets with biofuel and fossil fuel were proved to improve the fuel lubricity, cetane number, burning rate, chemical reaction, catalytic performance, fire/flash point, heat and mass transfer efficiency and water co-solvency as well as decrease delay period [ 76 , 77 ]. That resulted in more complete and cleaner combustion of microalgae biofuel mixed with fossil fuel in compression ignition (CI), spark ignition (SI), and direct ignition (DI) engines. In line with that, nano-technology applications showed the capability of amplifying microalgal-biofuel combustion efficiency and reduced soot, NO x , smoke, HC, CO 2, and CO emission to the environment up to 72% [ 6 , 76 , 78 ]. Application of solid nano-additives such as alumina (Al 2 O 3 ), CERIA, carbon nano-tubes (CNT), Co 3 O 4 , ZrO 2 , La 2 O 3 , CeO 2 , SiO 2 , Ni 2 O, TiO 2 , ZnO, Fe 2 O 3 , CuO, Ce x Zr (1– x ) O 2 , and amide-doped MWCNTs-CeO 2 boosted the engine power, torque, and brake thermal performance of biodiesel (extracted from microalgae and other biomass) in CI and DI engines up to 11% [ 59 , 76 , 79 , 80 ]. The experimental study of nano-particles on DI engines demonstrated that nano-particles blended with biodiesel as well as diesel–biodiesel mixture performed outstanding. The effectiveness was higher compared to usual catalysts [ 61 , 81 ]. Another study presented that nano-particles of CeO 2 incorporated with an emulsion of biofuel with sol–gel combustion technology performed excellent mono-cylinder 4 stroke direct CI and DI engines without any hardware modification. Nano-particles addition with biofuels escalated the fuel calorific value, fastened evaporation rate, improved brake-specific fuel consumptions and thermal efficiency, reduced greenhouse gases (GHGs) such as CO, NO x , and smoke, and unburned HCs. Chemical reactions between CeO 2 and GHGs gases are presented in Rc. 2 , Rc. 3 , and Rc. 4 [ 82 ]:
In contrast, liquid nano-additive, nano-Al-droplet application (nano-suspension) on biofuel mixture has been manifested more efficient than even micro-suspension. Liquid nano-additives also presented outstanding performance by achieving better suspension than n -decane-based fuels. Nano-Al suspension with ethanol was strong enough for a longer period than other particles, because ethanol tended to form a gel around the nano-particles due to higher viscosity [ 74 ]. Nano-droplets coated a monolayer on the mechanical parts of the engine touched with liquid fuel and improved fuel efficiency [ 18 ]. In addition, NPs such as nano-Al, Al 2 O 3 , CuO, MgO, MnO, and ZnO incorporated with water–diesel–biodiesel (E10) emulsion and bioethanol performed remarkably. Among these NPs, Al 2 O 3 performed the best because of mandate disabling, consistent torque boosting, higher heat of combustion, super-high DTG max value, tiniest size of water droplets, the minimum value of brake-specific fuel consumption, and lowest values of Soot, NO x , CO, and HC [ 19 , 83 ].
Challenges and future prospects
Although nano-additive applications played significant role in microalgae cultivation, harvesting, conversion to biofuel and biofuel applications to enhance the efficiency, yet some challenges remained before the implementation of nano-additives for the mercantile approach. Most of the nano-additives from experimental research were not well-characterized in terms of particle size, shape, and size distribution as well as clustering [ 84 ]. Before large-scale application, well characterization of nano-particles and nano-fluids must be studied comprehensively. Appropriate nano-additive selection, preparation methods, and time for the selected application should be emphasized for optimum productivity. The effect of nano-catalyst implementation for microalgae-biofuel combustion quality, engine performance, and gas emission should be well studied and well-understood before implementation. In line with that, the availability of appropriate nano-additives with large amount might be a challenge for mass application though for laboratory scale, nano-additives are adequately available. Another constraint is cost-effectiveness of nano-catalysts for an industrial application which may hinder the commercial perspective, since many nano-catalysts are quite expensive.
Along with the potential microalgae determination and biofuel generation, integration of a plant design of value-added co-products will be the predominant advantage of the overall project with the economical aspect. This review encouraged biofuel research and development (R&D) sector worldwide to convert their unused, abandoned and wastewater sources, wet, and barren lands into microalgae farm as an eminent source of biofuel production. However, it should be highlighted that based on the existing research experiments, microalgae fuel production still stands at initial stage due to downward economic profile worldwide. Nano-additive applications on microalgal biofuel are yet confined into laboratory and pilot scale which can be counted as a significant limitation. Hence, it is strongly recommended to figure out large-scale process development with nano-additive applications for enhancement of microalgal growth, biofuel transformation processes, and fuel utilization in CI and DI engines. Nano-additive applications at different stages from microalgae culture to end-product utilization have a strong possibility to gain economical feasibility. Therefore, the detailed techno-economic analysis must be commanded to determine whether NP applications on microalgae biofuel are economically favorable or not, since economical issue is one of the most effective factors behind large-scale plant setup. Besides, these applications also have positive impact on the environment with value-added co-product generation into near further. Since the nano-additive utilization manifested itself environment-friendly, still a comprehensive life cycle assessment should be conducted to present the environmental positivities transparently. Besides all these factors, public safety, impact on flora and fauna, and the possibility of bio-hazards are also needed to be analysed extensively before commercialization.
Microalgae utilization for biofuel production is undoubtedly desirable all over the world. Though this approach is energy-efficient and environment-friendly, experts are still looking for an innovation that can boost the microalgae-biofuel yield from primary stage to end product as well as shift the whole process towards a cost-effective fuel solution. Hence, this review was emphasized on the synergistic effect of nano-additive-enhanced microalgal biofuel for mercantile approach and fuel-yield extension. Application of various forms of nano-additives in different phases on microalgae growth to biofuel demonstrated an excellent outcome that may project revolutionary improvement of commercial microalgae biofuel. However, the sustainability analysis of stepwise production rounds for microalgae biofuel still presented a bare need of further research and innovative concepts. These concepts may determine the most appropriate nano-additive for the desired type of biofuel in the context of economical aspect. Since nano-additive application on microalgae is quite new research concept, policy making and implementation of nano-additives will remain as the most vital issues for commercial output especially in developing countries. Therefore, managerial insights are needed to be emphasized further on proper policy, socio-economic impact, advantages and limitations for the overall system to attract the government and non-government fuel industries.
Enhancement of microalgae cultivation and harvesting by nano-bubbles and nano-particles application.
Identification of suitable microalgae species, possible biofuels from microalgae, latest conversion technologies, processes, and required equipments.
Excellent microalgal-biofuel yield by nano-droplet and nano-additives.
Complete and cleaner combustion in fuel engines by nano-emulsion and nano-stabilizers.
Availability of data and materials
Not applicable.
Abbreviations
acetone–butanol–ethanol
silver nano-particles
silver oxide
airlift-loop bioreactor
aluminum oxide/alumina
aluminum droplet
bronsted acid
calcium carbonate
cerium oxide
calcium oxide
calcium oxide nano-particles blends
compression ignition
carbon-dioxide
carbon mono oxide
cobalt oxide
carbon nano-tubes
copper oxide
cerium–zirconium oxide
chitosan/magnetic nano-particles
direct ignition
deep eutectic solvent
maximum derivative thermogravimetry
free fatty acids
ferric oxide
ferric chloride
gallium aluminum arsenide
greenhouse gases
graphene oxide
hydro-carbon
5-hydroxymethyl furfural
lanthanum oxide
light-emitting diodes
localized surface plasmon resonance
multiwall carbon nano-tubes
mobil composition of matter No 41
magnesium oxide
manganese oxide
metal nano-particles
niobia/niobium oxide
nickel oxide
nitrogen oxide
oxidized MWNTs
polyacrylonitrile
photobioreactor
poly dimethylammonium chloride
research and development
rhodium oxide
santa barbara amorphous-15
supercritical water gasification (SCWG)
surface-functionalized iron-oxide nano-particles
spark ignition
silicon dioxide
simultaneous saccharification and co-fermentation
separate hydrolysis and co-fermentation
separate hydrolysis and fermentation
simultaneous saccharification and fermentation
strontium oxide
titanium dioxide
titanium silicalite-1
titanium dioxide silicate
alumino silicate mineral
zirconium dioxide
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Hossain, N., Mahlia, T.M.I. & Saidur, R. Latest development in microalgae-biofuel production with nano-additives. Biotechnol Biofuels 12 , 125 (2019). https://doi.org/10.1186/s13068-019-1465-0
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Received : 30 January 2019
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DOI : https://doi.org/10.1186/s13068-019-1465-0
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REVIEW article
Scope of algae as third generation biofuels.
- Biochemical Conversion Division, Sardar Swaran Singh National Institute of Renewable Energy, Kapurthala, Punjab, India
An initiative has been taken to develop different solid, liquid, and gaseous biofuels as the alternative energy resources. The current research and technology based on the third generation biofuels derived from algal biomass have been considered as the best alternative bioresource that avoids the disadvantages of first and second generation biofuels. Algal biomass has been investigated for the implementation of economic conversion processes producing different biofuels such as biodiesel, bioethanol, biogas, biohydrogen, and other valuable co-products. In the present review, the recent findings and advance developments in algal biomass for improved biofuel production have been explored. This review discusses about the importance of the algal cell contents, various strategies for product formation through various conversion technologies, and its future scope as an energy security.
Introduction
The requirement of energy for the mankind is increasing day by day. The major source of energy is based on fossil fuels only. Thus, the scarcity of fossil fuels, rising price of petroleum based fuels, energy protection, and increased global warming resulted in focusing on renewable energy sources such as solar, wind, hydro, tidal, and biomass worldwide ( Goldemberg and Guardabassi, 2009 ; Dragone et al., 2010 ; Rajkumar et al., 2014 ).
Different biomass from various sources like agricultural, forestry, and aquatic have been taken into consideration as the feedstocks for the production of several biofuels such as biodiesel ( Boyce et al., 2008 ; Yanqun et al., 2008 ), bioethanol ( Behera et al., 2014 ), biohydrogen ( Marques et al., 2011 ), bio-oil ( Shuping et al., 2010 ), and biogas ( Hughes et al., 2012 ; Singh et al., 2014 ). However, the environmental impact raised from burning of fuels has a great impact on carbon cycle (carbon balance), which is related to the combustion of fossil fuels. Besides, exhaustion of different existing biomass without appropriate compensation resulted in huge biomass scarcity, emerging environmental problems such as deforestation and loss of biodiversity ( Goldemberg, 2007 ; Li et al., 2008 ; Saqib et al., 2013 ).
Recently, researchers and entrepreneurs have focused their interest, especially on the algal biomass as the alternative feedstock for the production of biofuels. Moreover, algal biomass has no competition with agricultural food and feed production ( Demirbas, 2007 ). The photosynthetic microorganisms like microalgae require mainly light, carbon dioxide, and some nutrients (nitrogen, phosphorus, and potassium) for its growth, and to produce large amount of lipids and carbohydrates, which can be further processed into different biofuels and other valuable co-products ( Brennan and Owende, 2010 ; Nigam and Singh, 2011 ). Interestingly, the low content of hemicelluloses and about zero content of lignin in algal biomass results in an increased hydrolysis and/or fermentation efficiency ( Saqib et al., 2013 ). Other than biofuels, algae have applications in human nutrition, animal feed, pollution control, biofertilizer, and waste water treatment ( Thomas, 2002 ; Tamer et al., 2006 ; Crutzen et al., 2007 ; Hsueh et al., 2007 ; Choi et al., 2012 ). Therefore, the aim of the current review is to explore the scope of algae for the production of different biofuels and evaluation of its potential as an alternative feedstock.
Algae: Source of Biofuels
Generally, algae are a diverse group of prokaryotic and eukaryotic organisms ranging from unicellular genera such as Chlorella and diatoms to multicellular forms such as the giant kelp, a large brown alga that may grow up to 50 m in length ( Li et al., 2008 ). Algae can either be autotrophic or heterotrophic. The autotrophic algae require only inorganic compounds such as CO 2 , salts, and a light energy source for their growth, while the heterotrophs are non-photosynthetic, which require an external source of organic compounds as well as nutrients as energy sources ( Brennan and Owende, 2010 ). Microalgae are very small in sizes usually measured in micrometers, which normally grow in water bodies or ponds. Microalgae contain more lipids than macroalgae and have the faster growth in nature ( Lee et al., 2014a ). There are about more than 50,000 microalgal species out of which only about 30,000 species have been taken for the research study ( Surendhiran and Vijay, 2012 ; Richmond and Qiang, 2013 ; Rajkumar et al., 2014 ). The short harvesting cycle of algae is the key advantage for its importance, which is better than other conventional crops having harvesting cycle of once or twice in a year ( Chisti, 2007 ; Schenk et al., 2008 ). Therefore, the main focus has been carried out on algal biomass for its application in biofuel area.
There are several advantages of algal biomass for biofuels production: (a) ability to grow throughout the year, therefore, algal oil productivity is higher in comparison to the conventional oil seed crops; (b) higher tolerance to high carbon dioxide content; (c) the consumption rate of water is very less in algae cultivation; (d) no requirement of herbicides or pesticides in algal cultivation; (e) the growth potential of algal species is very high in comparison to others; (f) different sources of wastewater containing nutrients like nitrogen and phosphorus can be utilized for algal cultivation apart from providing any additional nutrient; and (g) the ability to grow under harsh conditions like saline, brackish water, coastal seawater, which does not affect any conventional agriculture ( Spolaore et al., 2006 ; Dismukes et al., 2008 ; Dragone et al., 2010 ). However, there are several disadvantages of algal biomass as feedstock such as the higher cultivation cost as compared to conventional crops. Similarly, harvesting of algae require high energy input, which is approximately about 20–30% of the total cost of production. Several techniques such as centrifugation, flocculation, floatation, sedimentation, and filtration are usually used for harvesting and concentrating the algal biomass ( Demirbas, 2010 ; Ho et al., 2011 ).
The algae can be converted into various types of renewable biofuels including bioethanol, biodiesel, biogas, photobiologically produced biohydrogen, and further processing for bio-oil and syngas production through liquefaction and gasification, respectively ( Kraan, 2013 ). The conversion technologies for utilizing algal biomass to energy sources can be categorized into three different ways, i.e., biochemical, chemical, and thermochemical conversion and make an algal biorefinery, which has been depicted in Figure 1 . The biofuel products derived from algal biomass using these conversion routes have been explored in detail in the subsequent sections.
Figure 1. Algal biomass conversion process for biofuel production .
Biodiesel Production
Biodiesel is a mixture of monoalkyl esters of long chain fatty acids [fatty acid methyl esters (FAME)], which can be obtained from different renewable lipid feedstocks and biomass. It can be directly used in different diesel engines ( Clark and Deswarte, 2008 ; Demirbas, 2009 ). Studies to explore the microalgae as feedstock for the production of liquid fuels had been started for the mid-1980s. In order to solve the energy crisis, the extraction of lipids from diatoms was attempted by some German scientists during the period of World War-II ( Cohen et al., 1995 ). The higher oil yield in algal biomass as compared to oil seed crops makes the possibility to convert into the biodiesel economically using different technologies. A comparative study between algal biomass and terrestrial plants for the production of biodiesel has been depicted in Table 1 . The oil productivity (mass of oil produced per unit volume of the microalgal broth per day) depends on the algal growth rate and the biomass content of the species. The species of microalgae such as Kirchneriella lunaris , Ankistrodesmus fusiformis , Chlamydocapsa bacillus , and Ankistrodesmus falcatus with high levels of polyunsaturated FAME are generally preferred for the production of biodiesel ( Nascimento et al., 2013 ). They commonly multiply their biomass with doubling time of 24 h during exponential growth. Oil content of microalgae is generally found to be very high, which exceed up to 80% by weight of its dry biomass. About 5,000–15,000 gal of biodiesel can be produced from algal biomass per acre per year, which reflects its potentiality ( Spolaore et al., 2006 ; Chisti, 2007 ).
Table 1 . Comparative study between algal biomass and terrestrial plants for biodiesel production .
However, there are some standards such as International Biodiesel Standard for Vehicles (EN14214) and American Society for Testing and Materials (ASTM), which are required to comply with the algal based biodiesel on the physical and chemical properties for its acceptance as substitute to fossil fuels ( Brennan and Owende, 2010 ). The higher degree of polyunsaturated fatty acids of algal oils as compared to vegetable oils make susceptible for oxidation in the storage and further limits its utilization ( Chisti, 2007 ). Some researchers have reported the different advantages of the algal biomass for the biodiesel production due to its high biomass growth and oil productivity in comparison to best oil crops ( Chisti, 2007 ; Hossain et al., 2008 ; Hu et al., 2008 ; Rosenberg et al., 2008 ; Schenk et al., 2008 ; Rodolfi et al., 2009 ; Mutanda et al., 2011 ).
Algal biodiesel production involves biomass harvesting, drying, oil extraction, and further transesterification of oil, which have been described as below.
Harvesting and Drying of Algal Biomass
Unicellular microalgae produce a cell wall containing lipids and fatty acids, which differ them from higher animals and plants. Harvesting of algal biomass and further drying is important prior to mechanical and solvent extraction for the recovery of oil. Macroalgae can be harvested using nets, which require less energy while microalgae can be harvested by some conventional processes, which include filtration ( Rossignol et al., 1999 ) flocculation ( Liu et al., 2013 ; Prochazkova et al., 2013 ), centrifugation ( Heasman et al., 2008 ), foam fractionation ( Csordas and Wang, 2004 ), sedimentation, froth floatation, and ultrasonic separation ( Bosma et al., 2003 ). Selection of harvesting method depends on the type of algal species.
Drying is an important method to extend shelf-life of algal biomass before storage, which avoids post-harvest spoilage ( Munir et al., 2013 ). Most of the efficient drying methods like spray-drying, drum-drying, freeze drying or lyophilization, and sun-drying have been applied on microalgal biomass ( Leach et al., 1998 ; Richmond, 2004 ; Williams and Laurens, 2010 ). Sun-drying is not considered as a very effective method due to presence of high water content in the biomass ( Mata et al., 2010 ). However, Prakash et al. (2007) used simple solar drying device and succeed in drying Spirulina and Scenedesmus having 90% of moisture content. Widjaja et al. (2009) showed the effectiveness of drying temperature during lipid extraction of algal biomass, which affects both concentration of triglycerides and lipid yield. Further, all these processes possess safety and health issues ( Singh and Gu, 2010 ).
Extraction of Oil from Algal Biomass
Unicellular microalgae produce a cell wall containing lipids and fatty acids, which differ them from higher animals and plants. In the literature, there are different methods of oil extraction from algae, such as mechanical and solvent extraction ( Li et al., 2014 ). However, the extraction of lipids from microalgae is costly and energy intensive process.
Mechanical oil extraction
The oil from nuts and seeds is extracted mechanically using presses or expellers, which can also be used for microalgae. The algal biomass should be dried prior to this process. The cells are just broken down with a press to leach out the oil. About 75% of oil can be recovered through this method and no special skill is required ( Munir et al., 2013 ). Topare et al. (2011) extracted oil through screw expeller by mechanical pressing (by piston) and osmotic shock method and recovered about 75% of oil from the algae. However, more extraction time is required as compared to other methods, which make the process unfavorable and less effective ( Popoola and Yangomodou, 2006 ).
Solvent based oil extraction
Oil extraction using solvent usually recovers almost all the oil leaving only 0.5–0.7% residual oil in the biomass. Therefore, the solvent extraction method has been found to be suitable method rather than the mechanical extraction of oil and fats ( Topare et al., 2011 ). Solvent extraction is another method of lipid extraction from microalgae, which involves two stage solvent extraction systems. The amount of lipid extracted from microalgal biomass and further yield of highest biodiesel depends mainly on the solvent used. Several organic solvents such as chloroform, hexane, cyclo-hexane, acetone, and benzene are used either solely or in mixed form ( Afify et al., 2010 ). The solvent reacts on algal cells releasing oil, which is recovered from the aqueous medium. This occurs due to the nature of higher solubility of oil in organic solvents rather than water. Further, the oil can be separated from the solvent extract. The solvent can be recycled for next extraction. Out of different organic solvents, hexane is found to be most effective due to its low toxicity and cost ( Rajvanshi and Sharma, 2012 ; Ryckebosch et al., 2012 ).
In case of using mixed solvents for oil extraction, a known quantity of the solvent mixture is used, for example, chloroform/methanol in the ratio 2:1 (v/v) for 20 min using a shaker and followed by the addition of mixture, i.e., chloroform/water in the ratio of 1:1 (v/v) for 10 min ( Shalaby, 2011 ). Similarly, Pratoomyot et al. (2005) extracted oil from different algal species using the solvent system chloroform/methanol in the ratio of 2:1 (v/v) and found different fatty acid content. Ryckebosch et al. (2012) optimized an analytical procedure and found chloroform/methanol in the ratio 1:1 as the best solvent mixture for the extraction of total lipids. Similarly, Lee et al. (1998) extracted lipid from the green alga Botryococcus braunii using different solvent system and obtained the maximum lipid content with chloroform/methanol in the ratio of 2:1. Hossain et al., 2008 used hexane/ether in the ratio 1:1 (v/v) for oil extraction and allowed to settle for 24 h. Using a two-step process, Fajardo et al. (2007) reported about 80% of lipid recovery using ethanol and hexane in the two steps for the extraction and purification of lipids. Therefore, a selection of a most suitable solvent system is required for the maximum extraction of oil for an economically viable process.
Lee et al. (2009) compared the performance of various disruption methods, including autoclaving, bead-beating, microwaves, sonication, and using 10% NaCl solution in the extraction of Botryococcus sp., Chlorella vulgaris , and Scenedesmus sp, using a mixture of chloroform and methanol (1:1).
Transesterification
This is a process to convert algal oil to biodiesel, which involves multiple steps of reactions between triglycerides or fatty acids and alcohol. Different alcohols such as ethanol, butanol, methanol, propanol, and amyl alcohol can be used for this reaction. However, ethanol and methanol are used frequently for the commercial development due to its low cost and its physical and chemical advantages ( Bisen et al., 2010 ; Surendhiran and Vijay, 2012 ). The reaction can be performed in the presence of an inorganic catalyst (acids and alkalies) or lipase enzyme. In this method, about 3 mol of alcohol are required for each mole of triglyceride to produce 3 mol of methyl esters (biodiesel) and 1 mol of glycerol (by-product) ( Meher et al., 2006 ; Chisti, 2007 ; Sharma and Singh, 2009 ; Surendhiran and Vijay, 2012 ; Stergiou et al., 2013 ) (Figure 2 ). Glycerol is denser than biodiesel and can be periodically or continuously removed from the reactor in order to drive the equilibrium reaction. The presence of methanol, the co-solvent that keeps glycerol and soap suspended in the oil, is known to cause engine failure ( Munir et al., 2013 ). Thus, the biodiesel is recovered by repeated washing with water to remove glycerol and methanol ( Chisti, 2007 ).
Figure 2. Transesterification of oil to biodiesel . R 1–3 are hydrocarbon groups.
The reaction rate is very slow by using the acid catalysts for the conversion of triglycerides to methyl esters, whereas the alkali-catalyzed transesterification reaction has been reported to be 4000 times faster than the acid-catalyzed reaction ( Mazubert et al., 2013 ). Sodium and potassium hydroxides are the two commercial alkali catalysts used at a concentration of about 1% of oil. However, sodium methoxide has become the better catalyst rather than sodium hydroxide ( Singh et al., 2006 ).
Kim et al. (2014) used Scenedesmus sp. for the biodiesel production through acid and alkali transesterification process. They reported 55.07 ± 2.18%, based on lipid by wt of biodiesel conversion using NaOH as an alkaline catalyst than using H 2 SO 4 as 48.41 ± 0.21% of biodiesel production. In comparison to acid and alkalies, lipases as biocatalyst have different advantages as the catalysts due to its versatility, substrate selectivity, regioselectivity, enantioselectivity, and high catalytic activity at ambient temperature and pressure ( Knezevic et al., 2004 ). It is not possible by some lipases to hydrolyze ester bonds at secondary positions, while some other group of enzymes hydrolyzes both primary and secondary esters. Another group of lipases exhibits fatty acids selectivity, and allow to cleave ester bonds at particular type of fatty acids. Luo et al. (2006) cloned the lipase gene lipB68 and expressed in Escherichia coli BL21 and further used it as a catalyst for biodiesel production. LipB68 could catalyze the transesterification reaction and produce biodiesel with a yield of 92% after 12 h, at a temperature of 20°C. The activity of the lipase enzyme with such a low temperature could provide substantial savings in energy consumption. However, it is rarely used due to its high cost ( Sharma et al., 2001 ).
Extractive transesterification
It involves several steps to produce biodiesel such as drying, cell disruption, oils extraction, transesterification, and biodiesel refining ( Hidalgo et al., 2013 ). The main problems are related with the high water content of the biomass (over 80%), which overall increases the cost of whole process.
In situ transesterification
This method skips the oil extraction step. The alcohol acts as an extraction solvent and an esterification reagent as well, which enhances the porosity of the cell membrane. Yields found are higher than via the conventional route, and waste is also reduced. Industrial biodiesel production involves release of extraction solvent, which contributes to the production of atmospheric smog and to global warming. Thus, simplification of the esterification processes can reduce the disadvantages of this attractive bio-based fuel. The single-step methods can be attractive solutions to reduce chemical and energy consumption in the overall biodiesel production process ( Patil et al., 2012 ). A comparison of direct and extractive transesterification is given in Table 2 .
Table 2 . Comparison of extractive transesterification and in situ methods ( Haas and Wagner, 2011 ) .
Bioethanol Production
Several researchers have been reported bioethanol production from certain species of algae, which produce high levels of carbohydrates as reserve polymers. Owing to the presence of low lignin and hemicelluloses content in algae in comparison to lignocellulosic biomass, the algal biomass have been considered more suitable for the bioethanol production ( Chen et al., 2013 ). Recently, attempts have been made (for the bioethanol production) through the fermentation process using algae as the feedstocks to make it as an alternative to conventional crops such as corn and soyabean ( Singh et al., 2011 ; Nguyen and Vu, 2012 ; Chaudhary et al., 2014 ). A comparative study of algal biomass and terrestrial plants for the production of bioethanol has been given in Table 3 . There are different micro and macroalgae such as Chlorococcum sp., Prymnesium parvum , Gelidium amansii , Gracilaria sp., Laminaria sp., Sargassum sp., and Spirogyra sp., which have been used for the bioethanol production ( Eshaq et al., 2011 ; Rajkumar et al., 2014 ). These algae usually require light, nutrients, and carbon dioxide, to produce high levels of polysaccharides such as starch and cellulose. These polysaccharides can be extracted to fermentable sugars through hydrolysis and further fermentation to bioethanol and separated through distillation as shown in Figure 3 .
Table 3 . Comparative study between algal biomass and terrestrial plants for bioethanol production .
Figure 3. Process for bioethanol production from microalgae .
Pre-Treatment and Saccharification
It has been reported that, the cell wall of some species of green algae like Spirogyra and Chlorococcum contain high level of polysaccharides. Microalgae such as C. vulgaris contains about 37% of starch on dry weight basis, which is the best source for bioethanol with 65% conversion efficiency ( Eshaq et al., 2010 ; Lam and Lee, 2012 ). Such polysaccharide based biomass requires additional processing like pre-treatment and saccharification before fermentation ( Harun et al., 2010 ). Saccharification and fermentation can also be carried out simultaneously using an amylase enzyme producing strain for the production of ethanol in a single step. Bioethanol from microalgae can be produced through the process, which is similar to the first generation technologies involving corn based feedstocks. However, there is limited literature available on the fermentation process of microalgae biomass for the production of bioethanol ( Schenk et al., 2008 ; John et al., 2011 ).
The pre-treatment is an important process, which facilitates accessibility of biomass to enzymes to release the monosaccharides. Acid pre-treatment is widely used for the conversion of polymers present in the cell wall to simple forms. The energy consumption in the pre-treatment is very low and also it is an efficient process ( Harun and Danquah, 2011a , b ). Yazdani et al. (2011) found 7% (w/w) H 2 SO 4 as the promising concentration for the pre-treatment of the brown macroalgae Nizimuddinia zanardini to obtain high yield of sugars without formation of any inhibitors. Candra and Sarinah (2011) studied the bioethanol production using red seaweed Eucheuma cottonii through acid hydrolysis. In this study, 5% H 2 SO 4 concentration was used for 2 h at 100°C, which yielded 15.8 g/L of sugars. However, there are other alternatives to chemical hydrolysis such as enzymatic digestion and gamma radiation to make it more sustainable ( Chen et al., 2012 ; Yoon et al., 2012 ; Schneider et al., 2013 ).
Similar to starch, there are certain polymers such as alginate, mannitol, and fucoidan present in the cell wall of various algae, which requires additional processing like pre-treatment and saccharification before fermentation. Another form of storage carbohydrate found in various brown seaweeds and microalgae is laminarin, which can be hydrolyzed by β-1,3-glucanases or laminarinases ( Kumagai and Ojima, 2010 ). Laminarinases can be categorized into two groups such as exo- and endo-glucanases based on the mode of hydrolysis, which usually produces glucose and smaller oligosaccharides as the end product. Both the enzymes are necessary for the complete digestion of laminarin polymer ( Lee et al., 2014b ).
Markou et al. (2013) saccharified the biomass of Spirulina ( Arthrospira platensis ), fermented the hydrolyzate and obtained the maximum ethanol yield of 16.32 and 16.27% (g ethanol /g biomass ) produced after pre-treatment with 0.5 N HNO 3 and H 2 SO 4 , respectively. Yanagisawa et al. (2011) investigated the content of polysaccharide materials present in three types of seaweeds such as sea lettuce ( Ulva pertusa ), chigaiso ( Alaria crassifolia ), and agar weed ( Gelidium elegans ). These seaweeds contain no lignin, which is a positive signal for the hydrolysis of polysaccharides without any pre-treatment. Singh and Trivedi (2013) used Spirogyra biomass for the production of bioethanol using Saccharomyces cerevisiae and Zymomonas mobilis . In a method, they followed acid pre-treatment of algal biomass and further saccharified using α-amylase producing Aspergillus niger . In another method, they directly saccharified the biomass without any pre-treatment. The direct saccharification process resulted in 2% (w/w) more alcohol in comparison to pretreated and saccharified algal biomass. This study revealed that the pre-treatment with different chemicals are not required in case of Spyrogyra , which reflects its economic importance for the production of ethanol. Also, cellulase enzyme has been used for the saccharification of algal biomass containing cellulose. However, this enzyme system is more expensive than amylases and glucoamylases, and doses required for effective cellulose saccharification are usually very high. Trivedi et al. (2013) applied different cellulases on green alga Ulva for saccharification and found highest conversion efficiency of biomass into reducing sugars by using cellulase 22119 rather than viscozyme L, cellulase 22086 and 22128. In this experiment, they found a maximum yield of sugar 206.82 ± 14.96 mg/g with 2% (v/v) enzyme loading for 36 h at a temperature of 45°C.
Fermentation
There are different groups of microorganisms like yeast, bacteria, and fungi, which can be used for the fermentation of the pretreated and saccharified algal biomass under anaerobic process for the production of bioethanol ( Nguyen and Vu, 2012 ). Nowadays, S. cerevisiae and Z. mobilis have been considered as the bioethanol fermenting microorganisms. However, fermentation of mannitol, a polymer present in certain algae is not possible in anaerobic condition using these well known microorganisms and requires supply of oxygen during fermentation, which is possible only by Zymobacter palmae ( Horn et al., 2000 ).
Certain marine red algae contain agar, a polymer of galactose and galactopyranose, which can be used for the production of bioethanol ( Yoon et al., 2010 ). The biomass of red algae can be depolymerized into different monomeric sugars like glucose and galactose. In addition to mannitol and glucose, brown seaweeds contain about 14% of extra carbohydrates in the form of alginate ( Wargacki et al., 2012 ). Horn et al. (2000) reported the presence of alginate, laminaran, mannitol, fucoidan, and cellulose in some brown seaweeds, which are good source of sugars. They fermented brown seaweed extract having mannitol using bacteria Z. palmae and obtained an ethanol yield of about 0.38 g ethanol/g mannitol.
In the literature, there are many advantages supporting microalgae as the promising substrate for bioethanol production. Hon-Nami (2006) used Chlamydomonas perigranulata algal culture and obtained different by-products such as ethanol and butanediol. Similarly, Yanagisawa et al. (2011) obtained glucose and galactose through the saccharification of agar weed (red seaweed) containing glucan and galactan and obtained 5.5% of ethanol concentration through fermentation using S. cerevisiae IAM 4178. Harun et al. (2010) obtained 60% more ethanol in case of lipid extracted microalgal biomass rather than intact algal biomass of Chlorococcum sp. This shows the importance of algal biomass for the production of both biodiesel and bioethanol.
Biogas Production
Recently, biogas production from algae through anaerobic digestion has received a remarkable attention due to the presence of high polysaccharides (agar, alginate, carrageenan, laminaran, and mannitol) with zero lignin and low cellulose content. Mostly, seaweeds are considered as the excellent feedstock for the production of biogas. Several workers have demonstrated the fermentation of various species of algae like Scenedesmus , Spirulina , Euglena , and Ulva for biogas production ( Samson and Leduy, 1986 ; Yen and Brune, 2007 ; Ras et al., 2011 ; Zhong et al., 2012 ; Saqib et al., 2013 ). The production of biogas using algal biomass in comparison to some terrestrial plants is shown in Table 4 .
Table 4 . Comparative study between algal biomass and terrestrial plants for biogas production .
Biogas is produced through the anaerobic transformation of organic matter present in the biodegradable feedstock such as marine algae, which releases certain gases like methane, carbon dioxide, and traces of hydrogen sulfide. The anaerobic conversion process involves basically four main steps. In the first step, the insoluble organic material and higher molecular mass compounds such as lipids, carbohydrates, and proteins are hydrolyzed into soluble organic material with the help of enzyme released by some obligate anaerobes such as Clostridia and Streptococci . The second step is called as acidogenesis, which releases volatile fatty acids (VFAs) and alcohols through the conversion of soluble organics with the involvement of enzymes secreted by the acidogenic bacteria. Further, these VFAs and alcohols are converted into acetic acid and hydrogen using acetogenic bacteria through the process of acetogenesis, which finally metabolize to methane and carbon dioxide by the methanogens ( Cantrell et al., 2008 ; Vergara-Fernandez et al., 2008 ; Brennan and Owende, 2010 ; Romagnoli et al., 2011 ).
Sangeetha et al. (2011) reported the anaerobic digestion of green alga Chaetomorpha litorea with generation of 80.5 L of biogas/kg of dry biomass under 299 psi pressure. Vergara-Fernandez et al. (2008) evaluated digestion of the marine algae Macrocystis pyrifera and Durvillaea antarctica marine algae in a two-phase anaerobic digestion system and reported similar biogas productions of 180.4 (±1.5) mL/g dry algae/day with a methane concentration around 65%. However, in case of algae blend, same methane content was observed with low biogas yield. Mussgnug et al. (2010) reported biogas production from some selected green algal species like Chlamydomonas reinhardtii and Scenedesmus obliquus and obtained 587 and 287 mL biogas/g of volatile solids, respectively. Further, there are few studies, which have been conducted with microalgae showing the effect of different pre-treatment like thermal, ultrasound, and microwave for the high production of biogas ( Gonzalez-Fernandez et al., 2012a , b ; Passos et al., 2013 ).
However, there are different factors, which limit the biogas production such as requirement of larger land area, infrastructure, and heat for the digesters ( Collet et al., 2011 ; Jones and Mayfield, 2012 ). The proteins present in algal cells increases the ammonium production resulting in low carbon to nitrogen ratio, which affects biogas production through the inhibition of growth of anaerobic microorganisms. Also, anaerobic microorganisms are inhibited by the sodium ions. Therefore, it is recommended to use the salt tolerating microorganisms for the anaerobic digestion of algal biomass ( Yen and Brune, 2007 ; Brennan and Owende, 2010 ; Jones and Mayfield, 2012 ).
Biohydrogen Production
Recently, algal biohydrogen production has been considered to be a common commodity to be used as the gaseous fuels or electricity generation. Biohydrogen can be produced through different processes like biophotolysis and photo fermentation ( Shaishav et al., 2013 ). Biohydrogen production using algal biomass is comparative to that of terrestrial plants (Table 5 ). Park et al. (2011) found Gelidium amansii (red alga) as the potential source of biomass for the production of biohydrogen through anaerobic fermentation. Nevertheless, they found 53.5 mL of H 2 from 1 g of dry algae with a hydrogen production rate of 0.518 L H 2 /g VSS/day. The authors found an inhibitor, namely, 5-hydroxymethylfurfural (HMF) produced through the acid hydrolysis of G. amansii that decreases about 50% of hydrogen production due to the inhibition. Thus, optimization of the pre-treatment method is an important step to maximize biohydrogen production, which will be useful for the future direction ( Park et al., 2011 ; Shi et al., 2011 ). Saleem et al. (2012) reduced the lag time for hydrogen production using microalgae Chlamydomonas reinhardtii by the use of optical fiber as an internal light source. In this study, the maximum rate of hydrogen production in the presence of exogenic glucose and optical fiber was reported to be 6 mL/L culture/h, which is higher than other reported values.
Table 5 . Comparative study between algal biomass and terrestrial plants for biohydrogen production .
Some of microalgae like blue green algae have glycogen instead of starch in their cells. This is an exception, which involves oxidation of ferrodoxin by the hydrogenase enzyme activity for the production of hydrogen in anaerobic condition. However, another function of this enzyme is to be involved in the detachment of electrons. Therefore, different researchers have focused for the identification of these enzyme activities having interactions with ferrodoxin and the other metabolic functions for microalgal photobiohydrogen production. They are also involved with the change of these interactions genetically to enhance the biohydrogen production ( Gavrilescu and Chisti, 2005 ; Hankamer et al., 2007 ; Wecker et al., 2011 ; Yacoby et al., 2011 ; Rajkumar et al., 2014 ).
Bio-Oil and Syngas Production
Bio-oil is formed in the liquid phase from algal biomass in anaerobic condition at high temperature. The composition of bio-oil varies according to different feedstocks and processing conditions, which is called as pyrolysis ( Iliopoulou et al., 2007 ; Yanqun et al., 2008 ). There are several parameters such as water, ash content, biomass composition, pyrolysis temperature, and vapor residence time, which affect the bio-oil productivity ( Fahmi et al., 2008 ). However, due to the presence of water, oxygen content, unsaturated and phenolic moieties, crude bio-oil cannot be used as fuel. Therefore, certain treatments are required to improve its quality ( Bae et al., 2011 ). Bio-oils can be processed for power generation with the help of external combustion through steam and organic rankine cycles, and stirling engines. However, power can also be generated through internal combustion using diesel and gas-turbine engines ( Chiaramonti et al., 2007 ). In literature, there are limited studies on algae pyrolysis compared to lignocellulosic biomass. Although, high yields of bio-oil occur through fluidized-bed fast pyrolysis processes, there are several other pyrolysis modes, which have been introduced to overcome their inherent disadvantages of a high level of carrier gas flow and excessive energy inputs ( Oyedun et al., 2012 ). Demirbas (2006) investigated suitability of the microalgal biomass for bio-oil production and found the superior quality than the wood. Porphy and Farid (2012) produced bio-oil from pyrolysis of algae ( Nannochloropsis sp.) at 300°C after lipid extraction, which composed of 50 wt% acetone, 30 wt% methyl ethyl ketone, and 19 wt% aromatics such as pyrazine and pyrrole. Similarly, Choi et al. (2014) carried out pyrolysis study on a species of brown algae Saccharina japonica at a temperature of 450°C and obtained about 47% of bio-oil yield.
Gasification is usually performed at high temperatures (800–1000°C), which converts biomass into the combustible gas mixture through partial oxidation process, called syngas or producer gas. Syngas is a mixture of different gases like CO, CO 2 , CH 4 , H 2 , and N 2 , which can also be produced through normal gasification of woody biomass. In this process, biomass reacts with oxygen and water (steam) to generate syngas. It is a low calorific gas, which can be utilized in the gas turbines or used directly as fuel. Different variety of biomass feedstocks can be utilized for the production of energy through the gasification process, which is an added advantage ( Carvalho et al., 2006 ; Prins et al., 2006 ; Lv et al., 2007 ).
Conclusion and Future Perspectives
Recently, it is a challenge for finding different alternative resources, which can replace fossil fuels. Due to presence of several advantages in algal biofuels like low land requirement for biomass production and high oil content with high productivity, it has been considered as the best resource, which can replace the liquid petroleum fuel. However, one of its bottlenecks is the low biomass production, which is a barrier for industrial production. Also, another disadvantage includes harvesting of biomass, which possesses high energy inputs. For an economic process development in comparison to others, a cost-effective and energy efficient harvesting methods are required with low energy input. Producing low-cost microalgal biofuels requires better biomass harvesting methods, high biomass production with high oil productivity through genetic modification, which will be the future of algal biology. Therefore, use of the standard algal harvesting technique, biorefinery concept, advances in photobioreactor design and other downstream technologies will further reduce the cost of algal biofuel production, which will be a competitive resource in the near future.
Conflict of Interest Statement
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Acknowledgments
The authors are thankful to Prof. Y. K. Yadav, Director, NIRE, Kapurthala for his consistent support to write this review paper. The authors greatly acknowledge the Ministry of New and Renewable Energy, New Delhi, Govt. of India, for providing funds to carry out research work.
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Keywords: algae, microalgae, biofuels, bioethanol, biogas, biodiesel, biohydrogen
Citation: Behera S, Singh R, Arora R, Sharma NK, Shukla M and Kumar S (2015) Scope of algae as third generation biofuels. Front. Bioeng. Biotechnol. 2 :90. doi: 10.3389/fbioe.2014.00090
Received: 31 July 2014; Accepted: 29 December 2014; Published online: 11 February 2015.
Reviewed by:
Copyright: © 2015 Behera, Singh, Arora, Sharma, Shukla and Kumar. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Sachin Kumar, Biochemical Conversion Division, Sardar Swaran Singh National Institute of Renewable Energy, Jalandhar-Kapurthala Road, Wadala Kalan, Kapurthala 144601, Punjab, India e-mail: sachin.biotech@gmail.com
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Yeast for the production of biochemicals and biofuels.
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Paul, D. Yeast for the Production of Biochemicals and Biofuels. Fermentation 2024 , 10 , 451. https://doi.org/10.3390/fermentation10090451
Paul D. Yeast for the Production of Biochemicals and Biofuels. Fermentation . 2024; 10(9):451. https://doi.org/10.3390/fermentation10090451
Paul, Debarati. 2024. "Yeast for the Production of Biochemicals and Biofuels" Fermentation 10, no. 9: 451. https://doi.org/10.3390/fermentation10090451
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Journal of Materials Chemistry A
Photo-nanozyme coupling catalyzes glucose oxidation for high-performance enzymatic biofuel cells.
Glucose biofuel cells (GBFCs) are special energy conversion devices using naturally abundant glucose as fuel. However, achieving high power output and stability remains a challenge in existing GBFC. In this study, we created a photoelectric coupling nanozyme catalyst of Au/BiVO 4 with triple synergistic promotion effects: the surface plasmon resonance of Au significantly broadened the photo-absorption region, enhanced the light absorption intensity, and increased the carrier density of the BiVO 4 ; furthermore, the outstanding electron transfer capacity of Au accelerated the photoelectrons separation from the vacancies in BiVO 4 , endowing the BiVO 4 with excellent photo-corrosion resistance; additionally, the three-dimensional structure of BiVO 4 provides abundant sites for Au, remarkably improving the loading and catalytic stability of Au. Consequently, the Au/BiVO 4 catalytic for GBFC can simultaneously convert solar and chemical energy stored in glucose into electrical energy, providing an extraordinarily high power density and open-circuit voltage (575 μW cm -2 , 0.86 V) and working steadily for 20 hours. Altogether, high power output and high stability are achieved in the Au/BiVO 4 catalytic GBFC. Thus, this study will significantly propel the development of GBFC through the innovative application of the photoelectric coupling nanozyme catalytic strategy.
- This article is part of the themed collection: Journal of Materials Chemistry A HOT Papers
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D. Hu, Q. Su, Y. Gao, J. Zhang, L. Wang and J. Zhu, J. Mater. Chem. A , 2024, Accepted Manuscript , DOI: 10.1039/D4TA04675G
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APA Style for beginners
Then check out some frequently asked questions:
What is APA Style?
Why use apa style in high school, how do i get started with apa style, what apa style products are available, your help wanted.
APA Style is the most common writing style used in college and career. Its purpose is to promote excellence in communication by helping writers create clear, precise, and inclusive sentences with a straightforward scholarly tone. It addresses areas of writing such as how to
- format a paper so it looks professional;
- credit other people’s words and ideas via citations and references to avoid plagiarism; and
- describe other people with dignity and respect using inclusive, bias-free language.
APA Style is primarily used in the behavioral sciences, which are subjects related to people, such as psychology, education, and nursing. It is also used by students in business, engineering, communications, and other classes. Students use it to write academic essays and research papers in high school and college, and professionals use it to conduct, report, and publish scientific research .
High school students need to learn how to write concisely, precisely, and inclusively so that they are best prepared for college and career. Here are some of the reasons educators have chosen APA Style:
- APA Style is the style of choice for the AP Capstone program, the fastest growing AP course, which requires students to conduct and report independent research.
- APA Style helps students craft written responses on standardized tests such as the SAT and ACT because it teaches students to use a direct and professional tone while avoiding redundancy and flowery language.
- Most college students choose majors that require APA Style or allow APA Style as an option. It can be overwhelming to learn APA Style all at once during the first years of college; starting APA Style instruction in high school sets students up for success.
High school students may also be interested in the TOPSS Competition for High School Psychology Students , an annual competition from the APA Teachers of Psychology in Secondary Schools for high school students to create a short video demonstrating how a psychological topic has the potential to benefit their school and/or local community and improve people’s lives.
Most people are first introduced to APA Style by reading works written in APA Style. The following guides will help with that:
|
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| Handout explaining how journal articles are structured and how to become more efficient at reading and understanding them |
| Handout exploring the definition and purpose of abstracts and the benefits of reading them, including analysis of a sample abstract |
Many people also write research papers or academic essays in APA Style. The following resources will help with that:
|
|
| Guidelines for setting up your paper, including the title page, font, and sample papers |
| More than 100 reference examples of various types, including articles, books, reports, films, social media, and webpages |
| Handout comparing example APA Style and MLA style citations and references for four common reference types (journal articles, books, edited book chapters, and webpages and websites) |
| Handout explaining how to understand and avoid plagiarism |
| Checklist to help students write simple student papers (typically containing a title page, text, and references) in APA Style |
| Handout summarizing APA’s guidance on using inclusive language to describe people with dignity and respect, with resources for further study |
| Free tutorial providing an overview of all areas of APA Style, including paper format, grammar and usage, bias-free language, punctuation, lists, italics, capitalization, spelling, abbreviations, number use, tables and figures, and references |
| Handout covering three starter areas of APA Style: paper format, references and citations, and inclusive language |
Instructors will also benefit from using the following APA Style resources:
|
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| Recording of a webinar conducted in October 2023 to refresh educators’ understanding of the basics of APA Style, help them avoid outdated APA Style guidelines (“zombie guidelines”), debunk APA Style myths (“ghost guidelines”), and help students learn APA Style with authoritative resources |
| Recording of a webinar conducted in May 2023 to help educators understand how to prepare high school students to use APA Style, including the relevance of APA Style to high school and how students’ existing knowledge MLA style can help ease the transition to APA Style (register for the webinar to receive a link to the recording) |
| Recording of a webinar conducted in September 2023 to help English teachers supplement their own APA Style knowledge, including practical getting-started tips to increase instructor confidence, the benefits of introducing APA Style in high school and college composition classes, some differences between MLA and APA Style, and resources to prepare students for their future in academic writing |
| Poster showing the three main principles of APA Style: clarity, precision, and inclusion |
| A 30-question activity to help students practice using the APA Style manual and/or APA Style website to look up answers to common questions |
In addition to all the free resources on this website, APA publishes several products that provide comprehensive information about APA Style:
|
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| The official APA Style resource for students, covering everything students need to know to write in APA Style |
| The official source for APA Style, containing everything in the plus information relevant to conducting, reporting, and publishing psychological research |
| APA Style’s all-digital workbook with interactive questions and graded quizzes to help you learn and apply the basic principles of APA Style and scholarly writing; integrates with popular learning management systems, allowing educators to track and understand student progress |
| APA’s online learning platform with interactive lessons about APA Style and academic writing, reference management, and tools to create and format APA Style papers |
The APA Style team is interested in developing additional resources appropriate for a beginner audience. If you have resources you would like to share, or feedback on this topic, please contact the APA Style team .
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- Everyday science
Researchers cut to the chase on the physics of paper cuts
If you have ever been on the receiving end of a paper cut, you will know how painful they can be.
Kaare Jensen from the Technical University of Denmark (DTU), however, has found intrigue in this bloody occurrence. “I’m always surprised that thin blades, like lens or filter paper, don’t cut well, which is unexpected because we usually consider thin blades to be efficient,” Jensen told Physics World .
To find out why paper is so successful at cutting skin, Jensen and fellow DTU colleagues carried out over 50 experiments with a range of paper thicknesses to make incisions into a piece of gelatine at various angles.
Through these experiments and modelling, they discovered that paper cuts are a competition between slicing and “buckling”. Thin paper with a thickness of about 30 microns, or 0.03 mm, doesn’t cut so well because it buckles – a mechanical instability that happens when a slender object like paper is compressed. Once this occurs, the paper can no longer transfer force to the tissue, so is unable to cut.
Thick paper, with a thickness greater than around 200 microns, is also ineffective at making an incision. This is because it distributes the load over a greater area, resulting in only small indentations.
The team found, however, a paper cut “sweet spot” at around 65 microns and when the incision was made at an angle of about 20 degrees from the surface. This paper thickness just happens to be close to that of the paper used in print magazines, which goes some way to explain why it annoyingly happens so often.
Using the results from the work, the researchers created a 3D-printed scalpel that uses scrap paper for the cutting edge. Using this so-called “papermachete” they were able to slice through apple, banana peel, cucumber and even chicken.
Jensen notes that the findings are interesting for two reasons. “First, it’s a new case of soft-on-soft interactions where the deformation of two objects intertwines in a non-trivial way,” he says. “Traditional metal knives are much stiffer than biological tissues, while paper is still stiffer than skin but around 100 times weaker than steel.”
The second is that it is a “great way” to teach students about forces given that the experiments are straightforward to do in the classroom. “Studying the physics of paper cuts has revealed a surprising potential use for paper in the digital age: not as a means of information dissemination and storage, but rather as a tool of destruction,” the researchers write.
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Research: How to Build Consensus Around a New Idea
- Devon Proudfoot
- Wayne Johnson
Strategies for overcoming the disagreements that can stymie innovation.
Previous research has found that new ideas are seen as risky and are often rejected. New research suggests that this rejection can be due to people’s lack of shared criteria or reference points when evaluating a potential innovation’s value. In a new paper, the authors find that the more novel the idea, the more people differ on their perception of its value. They also found that disagreement itself can make people view ideas as risky and make them less likely to support them, regardless of how novel the idea is. To help teams get on the same page when it comes to new ideas, they suggest gathering information about evaluator’s reference points and developing criteria that can lead to more focused discussions.
Picture yourself in a meeting where a new idea has just been pitched, representing a major departure from your company’s standard practices. The presenter is confident about moving forward, but their voice is quickly overtaken by a cacophony of opinions from firm opposition to enthusiastic support. How can you make sense of the noise? What weight do you give each of these opinions? And what does this disagreement say about the idea?
- DP Devon Proudfoot is an Associate Professor of Human Resource Studies at Cornell’s ILR School. She studies topics related to diversity and creativity at work.
- Wayne Johnson is a researcher at the Utah Eccles School of Business. He focuses on evaluations and decisions about new information, including persuasion regarding creative ideas and belief change.
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Yemen + 4 more
Crimes of Enforced Disappearance: A Research Paper Approaching the Issues and Envisioning Solutions [EN/AR]
Attachments.
Crimes of Enforced Disappearance
A Research Paper Addressing Challenges and Proposing Solutions
Mwatana for Human Rights, in partnership with the Smith Human Rights Clinic at Columbia Law School, has released a research paper titled "Crimes of Enforced Disappearance: Addressing Challenges and Proposing Solutions," coinciding with the International Day of the Victims of Enforced Disappearances, observed annually on August 30. The paper sheds light on the crimes of enforced disappearance committed by successive authorities over decades in Yemen, including those committed since the 1960s and during the ongoing armed conflict that began in September 2014.
The paper focuses on exploring potential mechanisms to address the burdened file of enforced disappearances in Yemen within the framework of transitional justice programs in the post-conflict phase. It discusses the challenges and issues related to the complete absence of accountability mechanisms, truth-seeking, uncovering the fate of the disappeared, and mechanisms for reparations for violations committed over the past decades up to the present.
The paper reviews the experiences of dealing with enforced disappearance and truth-seeking efforts in Syria, Sri Lanka, Argentina, and Colombia—contexts that have suffered from enforced disappearances for decades by different authorities and have developed effective mechanisms to address these issues. These experiences serve as valuable references when designing programs related to enforced disappearances in Yemen in the post-conflict phase.
Radhya Al-Mutawakel, Chairperson of Mwatana for Human Rights, stated, "It is time to explore possible ways to address the issue of enforced disappearance in Yemen and to work towards a future free of this brutal violation and its consequences." She added, "Studying other experiences that share similarities with Yemen's situation is crucial for understanding how other nations have dealt with complex issues like enforced disappearance in Yemen, the challenges they faced, and the ways they overcame them. It is also important to learn from the mistakes that accompanied those experiences to avoid them."
Mwatana emphasized that this paper is part of the organization’s efforts to address urgent elements and topics of transitional justice, which can provide well-considered inputs to guide transitional justice programs in Yemen and ensure their effectiveness. This will contribute to achieving sustainable peace, under which the dignity and freedoms of individuals are preserved, and the recurrence of human rights violations, particularly enforced disappearances, are prevented in the future.
Mwatana noted that thousands of Yemenis remain victims of enforced disappearance as a result of cycles of political conflict—crimes that continue to be passed down by the authorities and parties that have successively held power and led security agencies with their heavy legacy of victims of enforced disappearance, including forcibly disappeared individuals, their families, loved ones, and communities. This also includes hundreds of victims of enforced disappearance related to the current cycle of conflict, involving all local and regional parties.
Mwatana called on the international community, the United Nations, and international entities and institutions working in Yemen to ensure that their efforts and interventions in Yemen include comprehensive solutions for the crimes of enforced disappearance, uncovering the fate of the disappeared, reparations, accountability, compensation, and commemoration within the framework of comprehensive transitional justice. They also urged the formation of a criminal mechanism to investigate human rights violations, particularly enforced disappearance, and to work on strengthening the functioning of independent civil society organizations in monitoring the security and justice sectors, raising awareness, and building capacities.
Related Content
24 women receive economic empowerment grants, at least 214 arbitrary detentions recorded in august 2024, including 13 children and seven women [en/ar], rapid displacement tracking - yemen idp dashboard reporting period: 25 to 31 august 2024, driven by compassion: acts of kindness that change lives.
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Research News
The physics behind the most annoying thing that could ever happen to you: a paper cut, the physics behind a very annoying thing that could ever happen to you: a paper cut.
Scientists have figured out what type of paper is the most prone to cut skin. Kaare Jensen, associate professor of physics at the Technical University of Denmark, explains.
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[SIGGRAPH Asia 2024, Journal Track] ToonCrafter: Generative Cartoon Interpolation
Doubiiu/ToonCrafter
Folders and files.
Name | Name | |||
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512_interp | 512_interp | |||
Repository files navigation
Tooncrafter: generative cartoon interpolation, 🔆 introduction.
⚠️ Please check our disclaimer first.
🤗 ToonCrafter can interpolate two cartoon images by leveraging the pre-trained image-to-video diffusion priors. Please check our project page and paper for more information.
1.1 Showcases (512x320)
Input starting frame | Input ending frame | Generated video |
1.2 Sparse sketch guidance
Input starting frame | Input ending frame | Input sketch guidance | Generated video |
2. Applications
2.1 cartoon sketch interpolation (see project page for more details).
Input starting frame | Input ending frame | Generated video |
2.2 Reference-based Sketch Colorization
Input sketch | Input reference | Colorization results |
📝 Changelog
- Add sketch control and colorization function.
- [2024.05.29] : 🔥🔥 Release code and model weights.
- [2024.05.28] : Launch the project page and update the arXiv preprint.
Model | Resolution | GPU Mem. & Inference Time (A100, ddim 50steps) | Checkpoint |
---|---|---|---|
ToonCrafter_512 | 320x512 | TBD ( ) |
Currently, our ToonCrafter can support generating videos of up to 16 frames with a resolution of 512x320. The inference time can be reduced by using fewer DDIM steps.
Install Environment via Anaconda (Recommended)
💫 inference, 1. command line.
Download pretrained ToonCrafter_512 and put the model.ckpt in checkpoints/tooncrafter_512_interp_v1/model.ckpt .
2. Local Gradio demo
Download the pretrained model and put it in the corresponding directory according to the previous guidelines.
📢 Disclaimer
Calm down. Our framework opens up the era of generative cartoon interpolation, but due to the variaity of generative video prior, the success rate is not guaranteed.
⚠️ This is an open-source research exploration, instead of commercial products. It can't meet all your expectations.
This project strives to impact the domain of AI-driven video generation positively. Users are granted the freedom to create videos using this tool, but they are expected to comply with local laws and utilize it responsibly. The developers do not assume any responsibility for potential misuse by users.
- Python 99.3%
The Federalist Papers
7 h total length
Discover the Genius of the Constitution
Thomas Jefferson described The Federalist Papers as “the best commentary on the principles of government, which ever was written.”
In this free ten-lecture course you will gain a deeper understanding of the purpose and structure of the American Founding by studying the arguments of America’s most influential Founders. Written between October 1787 and August 1788, The Federalist Papers is a collection of newspaper essays written by James Madison, Alexander Hamilton, and John Jay in defense of the Constitution.
Taught by Hillsdale College’s politics faculty, this course explores the major themes of this classic work of American politics, such as the problem of majority faction, the importance of separation of powers, the nature of the three branches of government, and the argument concerning the Bill of Rights.
By enrolling in this course you will receive free access to the course lectures, readings, and quizzes to aid you in this examination of the greatest Constitution ever written.
We invite you to join us today in this urgent study of the Constitution and what has been lost by the modern assault on it.
Expand Course Details
Lessons in this course.
Introduction: Articles of Confederation and the Constitutional Convention
Written following the Constitutional Convention of 1787, The Federalist Papers is the foremost American contribution to political thought. Originally published as newspaper essays in New York, they were written by Alexander Hamilton, James Madison, and John Jay under the pen name Publius. The essays defended the merits of the Constitution as a necessary and good replacement for the Articles of Confederation, which had proven defective as a means of governance.
The Improved Science of Politics
Publius argued that the “science of politics . . . has received great improvement” in his own day. These improvements include separation of powers, legislative checks and balances, judges who serve a life term during good behavior, and what he called “the ENLARGEMENT of the ORBIT” of government. Contrary to the practice of previous republics, Publius argued that a republic had a much greater chance of achieving success if it is spread out over a large or extended territory, rather than a small or contracted one.
The Problem of Majority Faction
In Federalist 10, Publius confronts one of the most important Anti-Federalist arguments against ratification: Republican government is impossible on a territory as large as the United States. In fact, such an undertaking had never been successful. In response, Publius proposes that the principal remedy for the political disease of faction—a disease “most incident to republican government”—is the large or extended sphere or territory.
Federalism and Republicanism
In the summer of 1787, the Framers labored to set up a political regime that would not only secure liberty and republicanism, but also bring energy and stability to the national government. Because of the failures of government under the Articles of Confederation, American political institutions were at risk. In order to secure these institutions, the Framers constructed a republican form of government that—among many other important features—instituted a new form of federalism.
Separation of Powers
In constituting a new government, the Framers knew that written rules—what Publius calls “parchment barriers”—would not be enough by themselves to protect liberty and prevent tyranny. Instead, Publius looks to the “interior structure” as the best means for keeping the branches properly and effectively separated. Separation of powers, the most important of the Constitution’s “auxiliary precautions,” works to prevent governmental tyranny, and by keeping each branch within its proper sphere of authority allows each branch to do its job well.
The Legislative: House and Senate
The Founders understood that the legislative branch is by nature the most powerful in a republican government. Experience of government under the Articles of Confederation, when state legislatures routinely encroached on executive and judicial powers, confirmed this. Thus, the Framers divided the legislative branch into two parts—the House and the Senate. In addition, they differentiated them as much as possible, consistent with the principles of republican government, with the goal of preventing tyranny and encouraging good government.
The Executive
Following their experience under the Articles of Confederation, and armed with the improved science of politics, the Framers instituted a unitary executive in the office of the president. Unlike the executive office in any previous republic, it was designed so as to ensure energy and responsibility in the executive, which are absolutely essential for good execution of the laws, and therefore for good government.
The Judiciary
In the Declaration of Independence, one charge leveled against King George III was that he had “made Judges dependent on his Will alone.” In framing a republican government, the Founders believed that an independent judiciary was indispensable. Publius argues that the term of life tenure during good behavior and a protected salary ensure this independence.
“The Constitution Is Itself . . . a Bill of Rights”
In Federalist 84, Publius writes, “The truth is, after all the declamation we have heard, that the constitution is itself, in every rational sense, and to every useful purpose, A BILL OF RIGHTS.” In other words, the structure of the Constitution protects the rights of the people. In addition, the American people retain all powers not granted to the federal and state governments.
Conclusion: Constitutionalism Today
American government today is much different from the constitutional republic outlined in The Federalist Papers —which relies on structure, representation, and limitations on the functions of the federal government. Administrative regulations and entitlements are two distinguishing features of modern government. These new features require a kind of government that is unlimited, disregards separation of powers, and violates the supreme law under which it claims to operate.
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Enroll in this free online course on the federalist papers today.
What Current Students Are Saying
The instructors are very good. The tests make you think. There are other helpful discussion screens and the whole process makes it feel much like a classroom setting. I feel the Federalist Papers are somewhat difficult to read on your own, so this course makes it much easier to understand.
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However, scientific research has shown that various biofuels differ massively in the greenhouse gas balance when compared with petrol despite the potential advantages. Based on the techniques used for processing the fuel and production of the feedstock, certain crops may also emit more greenhouse gases than fossil fuels do [52], [53]. 3.2.
This paper reviews and compares different strategies for biofuel production and concludes about their reliability against conventional fuels. It considers the feasibility and effectiveness behind using first, second and third-generation biofuels and draws a comparison between top countries their energy consumption rate and methods for reducing it.
Second- and third-generation biofuels are often referred to as 'advanced biofuels' as their production techniques or pathways are still in the research and development, pilot or demonstration phase. In this paper, the terminology 'first, second and third generation' has been selected and followed throughout.
Predominantly, biofuels are produced from photosynthetic organisms. such as photosynthetic bacteria, micro- and macro-algae and vascular land plants. The. primary products of biofuel may be in a ...
Biofuels are fuels produced from hydrocarbon-rich living organisms (biomass) — such as plants or microalgae — by thermal, chemical or biochemical conversion processes. As with fuels, biofuels ...
However, to fully exploit all the positive traits of biofuels, further research and investments are necessary, as the production of biofuels requires more processing steps compared with the conventional methods of drilling into the ground to obtain crude oil, followed by refining. ... Melcher F, Paper M, Brück TB. 9 Photosynthetic conversion ...
India's National Policy on Biofuels in 2009 proposed a non-mandatory target of a 20% blend for both biodiesel and ethanol by 2017, and outlines a broad strategy for the biofuels program and policy ...
Biofuel technology has evolved through several generations of significant advancements. The predominant problem with first-generation biofuels is that they are derived from food crops (e.g., corn and sugar cane), which require fertilization, water, and soil, and thus directly compete with food production. ... This is a novel research area that ...
Abstract. Bioethanol, a renewable and sustainable b iofuel, has eme rged as a promising. solution to address environmental and energy challenges. This comprehensive. review explores the historical ...
As biofuel research continues at an unprecedented rate, the development of new feedstocks and improvements in bioenergy production processes provide the key to the transformation of biomass into a global energy resource. ... Once your paper has been assessed for suitability by the editor, it will then be double anonymized peer-reviewed by ...
The aim of sustainability is to ensure continuous growth of the economy while protecting the environment and societal needs. Thus, this paper aims to evaluate the sustainability of these four generations of biofuels. The objectives are to compare the production of biofuel, the net greenhouse gases emissions, and energy efficiency.
Carbon-efficient biofuel production. An important aspect of microbial production of biofuels is the conservation of carbon that is converted from biomass substrates to fuel products. A challenge ...
Research on biofuel governance and other studies in the field of sustainability are most often based on a positive perception of power in the sense of power with.Power with is a term that refers to processes of developing shared values, finding common ground, and generating collective strengths [].This conception does not necessarily refer to the diffusion of already existing (predefined) norms.
The present article is not a regular review paper, but rather introduction to the fuel/biofuel research area with historical reminiscence and expectations for future developments. The readers might be surprised with information about fuel cells explored and practically used long time ago - the history might be surprising sometimes when it is ...
Cover art by BiofuelResJ. ©2024. Biofuel Research Journal (BRJ) is a leading, peer-reviewed academic journal dedicated to publishing high-quality research on biofuels, bioproducts, and related biomass-derived materials and technologies. BRJ is an open-access online journal and completely free-of-charge, aiming to advance knowledge and ...
Background Microalgae have been experimented as a potential feedstock for biofuel generation in current era owing to its' rich energy content, inflated growth rate, inexpensive culture approaches, the notable capacity of CO2 fixation, and O2 addition to the environment. Currently, research is ongoing towards the advancement of microalgal-biofuel technologies. The nano-additive application ...
An initiative has been taken to develop different solid, liquid, and gaseous biofuels as the alternative energy resources. The current research and technology based on the third generation biofuels derived from algal biomass have been considered as the best alternative bioresource that avoids the disadvantages of first and second generation ...
3rd generation biofuels like biohydrogen produced by microbial dark fermentation. • Agricultural waste can be used to generate energy, handmade paper, and fuel. • Microbial degradation approaches, phytoremediation and nanobiotechnology. • Biofuel and bioenergy produce from various agricultural waste,
Biofuel Research Journal Biofuel Research Journal (BRJ) is a leading, peer-reviewed academic journal dedicated to publishing high-quality research on biofuels, bioproducts, and related biomass-derived materials and technologies. BRJ is an open-access online journal and completely free-of-charge, aiming to advance knowledge and understanding
The first and third research articles (chronological order) focus on the use of Saccharomyces cerevisiae for 2,3-butanediol (BD) production, and the fourth on γ-bisabolene production from S. cerevisiae using various strategies. Liu et al. (contribution 1) show that the addition of exogenous short-chain fatty acids, acetic acid, and dissolved oxygen impacted the BD production from S ...
Glucose biofuel cells (GBFCs) are special energy conversion devices using naturally abundant glucose as fuel. However, achieving high power output and stability remains a challenge in existing GBFC. In this study, we created a photoelectric coupling nanozyme catalyst of Au/BiVO4 with triple synergistic promo Journal of Materials Chemistry A HOT Papers
Students use it to write academic essays and research papers in high school and college, and professionals use it to conduct, report, and publish scientific research. Why use APA Style in high school? High school students need to learn how to write concisely, precisely, and inclusively so that they are best prepared for college and career. Here ...
Through these experiments and modelling, they discovered that paper cuts are a competition between slicing and "buckling". Thin paper with a thickness of about 30 micrometres, or 0.03 mm, doesn't cut so well because it buckles - a mechanical instability that happens when a slender object like paper is compressed.
Production of biodiesel, biogas. and bioethanol from various feedstock, several kinds of wastes, many types of. biomass and agricultural residues, is ecological viable and sustainable option. The ...
New research suggests that this rejection can be due to people's lack of shared criteria or reference points when evaluating a potential innovation's value. In a new paper, the authors find ...
Recently, more research is carried out in biofuels production from different plants and microbial originated biomass material because of its eco-friendly nature to the environment and being carbon neutral resources. Moreover, these plants and algae can accumulate biomass due to photosynthesis (Hwang et al., 2016, Voloshin et al., 2015). Due to ...
The paper sheds light on the crimes of enforced disappearance committed by successive authorities over decades in Yemen, including those committed since the 1960s and during the ongoing armed ...
Scientists have figured out what type of paper is the most prone to cut skin. Kaare Jensen, associate professor of physics at the Technical University of Denmark, explains.
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Written between October 1787 and August 1788, The Federalist Papers is a collection of newspaper essays written by James Madison, Alexander Hamilton, and John Jay in defense of the Constitution. Taught by Hillsdale College's politics faculty, this course explores the major themes of this classic work of American politics, such as the problem ...