research paper in biofuel

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• Review Article
• 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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• Applied microbiology
• 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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A standard measure of an engine or aviation fuel capability against compression.

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(ILs). A highly efficient set of reagents for the depolymerization and deconstruction of a range of feedstocks.

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Biofuel research: perceptions of power and transition

• Lena Partzsch 1  

Energy, Sustainability and Society volume  7 , Article number:  14 ( 2017 ) Cite this article

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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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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.

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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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Why is breaking down plant material for biofuels so slow?

How molecular roadblocks slow the breakdown of cellulose, an abundant renewable resource in plants.

Cellulose, which helps give plant cell walls their rigid structure, holds promise as a renewable raw material for biofuels -- if researchers can accelerate the production process. Compared to the breakdown of other biofuel materials like corn, breaking down cellulose is slow and inefficient but could avoid concerns around using a food source while taking advantage of abundant plant materials that might otherwise go to waste. New research led by Penn State investigators has revealed how several molecular roadblocks slow this process.

The team's most recent study, published in the Proceedings of the National Academy of Sciences , describes the molecular process by which cellobiose -- a two-sugar fragment of cellulose that is made during cellulose deconstruction -- can clog up the pipeline and interfere with subsequent cellulose breakdown.

Biofuel production relies on the breakdown of compounds like starch or cellulose into glucose, which can then be efficiently fermented into ethanol for use as a fuel or converted into other useful materials. The predominant biofuel option on the market today is generated from corn, in part because, the researchers said, their starches break down easily.

"There are several concerns about using corn as a biofuel source, including competing with the global food supply and the large quantity of greenhouse gasses produced when generating corn-based ethanol," said Charles Anderson, professor of biology in the Penn State Eberly College of Science and an author of the paper. "A promising alternative is to break down cellulose from the non-edible parts of plants like corn stalks, other plant waste like forestry residue, and potentially dedicated crops that could be grown on marginal land. But one of the major things holding back so-called second-generation biofuels from being economically competitive is that the current process to break down cellulose is slow and inefficient."

We have been using a relatively new imaging technique to explore the molecular mechanisms that slow down this process."

Cellulose is composed of chains of glucose, held together by hydrogen bonds into crystalline structures. Scientists use enzymes called cellulases, derived from fungi or bacteria, to break down plant material and extract the glucose from the cellulose. But, the researchers said, cellulose's crystalline structure paired with other compounds called xylan and lignin -- also present in cell walls -- provide additional challenges to the cellulose breakdown. Traditional techniques, however, were unable to reveal the specific molecular mechanisms of these slowdowns.

To explore these unclear mechanisms, the researchers chemically tagged individual cellulases with fluorescent markers. They then used Penn State's SCATTIRSTORM microscope, which the team designed and built for this very purpose, to trace the molecules through each step of the breakdown process and interpreted the resulting videos using computational processing and biochemical modeling.

"Traditional methods observe the breakdown process at a larger scale, artificially manipulate the position of the enzyme or only capture molecules in motion, which means you may miss some of the naturally occurring process," said Will Hancock, professor of biomedical engineering in the Penn State College of Engineering and an author of the paper. "Using the SCATTIRSTORM microscope, we were able to watch individual cellulase enzymes in action to really get at what is slowing down this process and generate new ideas for how to make it more efficient."

The researchers specifically studied the effect of a fungal cellulase enzyme called Cel7A. As part of the breakdown process, Cel7A feeds cellulose into a sort of molecular tunnel, where it is chopped up.

"Cel7A moves the glucose chain to the 'front door' of the tunnel, the chain is cleaved, and the products come out the 'back door' in a sort of pipeline," said Daguan Nong, assistant research professor of biomedical engineering in the Penn State College of Engineering and first author of the paper. "We aren't exactly sure how the enzyme threads the glucose chain to the tunnel or what exactly goes on inside, but we knew from previous studies that the product that comes out the back door, cellobiose, can interfere with the processing of subsequent cellulose molecules. Now, we know more about how it is interfering."

Within the tunnel, Cel7A chops up cellulose -- which has repeating units of glucose -- into two-sugar cellobiose fragments. The researchers found that cellobiose in solution can bind to the "back door" of the tunnel, which can slow down the exit of subsequent cellobiose molecules as it essentially blocks the way. Additionally, they found that it can bind to Cel7A near the front door, preventing the enzyme from binding to additional cellulose.

"Because cellobiose is so similar to cellulose, it's maybe not surprising that the little pieces can get into the tunnel," Hancock said. "Now that we have a better understanding of how exactly cellobiose is mucking things up, we can explore new ways to fine tune this process. For example, we could alter the front or the back door of the tunnel or change aspects of the Cel7A enzyme to be more efficient at preventing this inhibition. There has been a lot of work to engineer more efficient cellulase enzymes over the last two decades, and it's an incredibly powerful approach. Having a better understanding of the molecular mechanisms that limit cellulose degradation will help us direct this effort."

This research builds off recent work by the research team to understand other roadblocks to the degradation process -- xylan and lignin -- which they published recently in RSC Sustainability and Biotechnology for Biofuels and Bioproducts.

"We found that xylan and lignin operate in different ways to interfere with the breakdown of cellulose," said Nerya Zexer, postdoctoral researcher in biology in the Penn State Eberly College of Science and lead author of the RSC Sustainability paper. "Xylan coats the cellulose, reducing the proportion of the enzymes that can bind to and move cellulose. Lignin inhibits the enzyme's ability to bind to cellulose as well as its movement, reducing the velocity and distance of the enzyme."

Although strategies exist to remove components like xylan and lignin from the cellulose, the researchers said the removal of cellobiose is more difficult. One method uses a second enzyme to cleave cellobiose, but it adds additional cost and complexity to the system.

"About 50 cents per gallon of bioethanol production costs is dedicated just to enzymes, so minimizing this cost would do a lot in terms of making bioethanol from plant waste more competitive with fossil fuels or corn-based ethanol," Anderson said. "We will continue to investigate how to engineer enzymes and explore how enzymes might work together with the goal of making this process as low-cost and efficient as possible."

The research team at Penn State also includes Zachary Haviland, undergraduate student majoring in biomedical engineering at the time of the research; Sarah Pfaff, graduate student in biology at the time of the research; Daniel Cosgrove, Holder of the Eberly Family Chair in Biology; Ming Tien, professor emeritus of biochemistry and molecular biology; and Alec Paradiso, undergraduate student majoring in biotechnology.

Funding from the U.S. Department of Energy (DOE) and the U.S. National Science Foundation supported this work, including the construction of the SCATTIRSTORM microscope. Additional support was provided by the Center for Lignocellulose Structure and Formation, an Energy Frontier Research Center funded by the DOE.

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Materials provided by Penn State . Original written by Gail McCormick. Note: Content may be edited for style and length.

Journal Reference :

• Daguan Nong, Zachary K. Haviland, Nerya Zexer, Sarah A. Pfaff, Daniel J. Cosgrove, Ming Tien, Charles T. Anderson, William O. Hancock. Single-molecule tracking reveals dual front door/back door inhibition of Cel7A cellulase by its product cellobiose . Proceedings of the National Academy of Sciences , 2024; 121 (18) DOI: 10.1073/pnas.2322567121

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Production of a Butanol Based Biofuel from Second Generation Feedstock; What Does it Mean to be Green?

The electrification and decarbonization effort has reached a fever pitch in recent years. The drive to reduce greenhouse emissions and implement sustainable technologies has gained widespread support and seen several legislative victories. One area of sustainability that has received widespread investment are biofuels. Biofuels are used in the same systems as traditional gasoline and diesel, but they are created through biological mechanisms such as fermentation instead of crude oil distillation. By creating fuel this way, no additional carbon emissions are dispersed to the atmosphere, effectively halting a large portion of transportation related carbon emissions. One promising biofuel is Butanol. Butanol has favorable energy density compared to other commercial biofuels and can be used as a gasoline additive or replacement. While the concept of green technology like this seems great in theory, in practice some significant humanitarian challenges have arisen. Many of these challenges are evident in the extraction of metals like lithium and cobalt, while these materials are not used in the production of biofuels, they are used to produce batteries for electric vehicles, laptops, phones, and more. Furthermore, the definition of a "green" technology is often vague, nebulous, and often developed to misinform consumers. I believe that In order to "close the loop" on sustainable technologies considerable effort needs to be given to harmonize marketing around sustainable technologies and humanize the processes through which we create them.

The technical portion of this thesis centered around the creation of a theoretical biobutanol production plant. This facility is designed to produce 57 million kilograms of butanol every year, which is similar to a typical ethanol production facility. Ethanol is currently the most widely produced biofuel, but switching to butanol offers significant increases in product energy density, lower volatility, and an increased compatibility with existing combustion engines. This plant uses "ABE" fermentation to generate acetone, butanol, and ethanol products. This process entails the use of Clostridium acetobutylicum bacteria to convert glucose derived from corn stover into usable biofuels. Notably, the feedstock for this plant is second generation corn stover which is comprised of the inedible parts of a cornstalk. This is significant because virtually all current biofuel plants use first generation feedstocks, which are edible foods now being used to make fuel instead of feeding people. Furthermore, our plant uses a pervaporation process to purify the butanol from the other components that the plant creates. This process is more energy efficient than the traditional distillation techniques used historically. The plant also generates a significant amount of calcium hydrogen phosphate enriched animal feed that serves as the primary revenue driver for the plant.

In the sociotechnical portion of this thesis, I examine the dishonestly around "green" products by looking at the resource extraction industry through the Actor Network Theory framework. The resource extraction industry is notorious for abusing labor and destroying communities, especially in low-income countries. First, a review of the typical development of these industries is conducted to highlight how the subjugative relationship between resource extraction companies and local communities’ forms. Next, an analysis is conducted of a potent example of these relationships: the current environment in the Democratic Republic of the Congo, specifically as it related to cobalt extraction. This situation highlights the dire need for some form of regulatory or humanitarian intervention in the industry, as the detrimental and irreversible impacts the industry is having on the Congolese people grow worse by the day. I continue by proposing ideas to attempt to mitigate the damage being done, and to encourage the use of regulations and involvement of nonprofit groups to mediate. Lastly, I enumerate how truly sustainable extraction practices could be marketed and supported by corporations and consumers to increase equity and transparency.

The purpose of considering a seeming unrelated industry- resource extraction- in a project centered about biofuel is in the hope that the world could learn from its mistakes. I think the global consensus is that society needs to move away from fossil fuels and towards a society that does not actively destroy its home planet. However, in the current climate, it is the most impoverished among us who are bearing the ugly burdens of the rest of society. This is not sustainable in the long term, and the sooner we are able to remedy current injustices, the sooner we will be able to develop a framework for creating ethical and equitable processes that deliver holistically sustainable technologies across a wide range of applications.

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The time-varying dynamic impact of US renewable energy prices on agricultural prices in China: the case of fuel ethanol

• Research Article
• Published: 10 May 2024

Cite this article

• Lianlian Fu 1 ,
• Xinqi Tu   ORCID: orcid.org/0009-0000-3443-7954 1 &
• Dongyu Yuan 1  

This paper intends to look into the time-varying dynamic impact of US fuel ethanol, one of the renewable energy sources, on the prices of agricultural products (specifically corn, soybeans, rice, and wheat) in China based on monthly price data from January 2000 to January 2023. To achieve this, a time-varying parameter vector autoregressive (TVP-VAR) model is employed, which takes into account structural changes in emergencies through time-varying parameters. The empirical results show that the equal-interval impulse responses of price fluctuations in agricultural commodities are primarily positive to variations in fuel ethanol prices and production. And the intensity and direction of the effects vary at distinct time lags. Additionally, the magnitude of these responses is most pronounced in the short term for all agricultural commodities except for corn, and the duration of the impulse responses at different time points is generally longer for corn prices compared to other commodities. The study also reveals that the influence of US fuel ethanol on Chinese agricultural commodity prices is not substantial on the whole. Therefore, there is a necessity to advance the growth of biofuels and provide policy support and financial subsidies for agricultural products earmarked for food production. These actions could shed insights into the progression of Chinese renewable energy and food policies, ensuring the stability of the market in the long run.

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Acknowledgements

The authors are grateful for the time and effort of the selected experts, whose decisions were crucial in achieving the objectives of this work.

This work was supported by grants from the National Natural Science Foundation of China (No: 72363019 & 71963019).

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Dynamic simulation path: soybean

Dynamic simulation path: rice

Dynamic simulation path: wheat

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Fu, L., Tu, X. & Yuan, D. The time-varying dynamic impact of US renewable energy prices on agricultural prices in China: the case of fuel ethanol. Environ Sci Pollut Res (2024). https://doi.org/10.1007/s11356-024-33480-x

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NREL Biomass Technology a Cornerstone of SAFFiRE Renewables Biofuel Pilot Plant Going Up in Kansas

Working with southwest airlines, conestoga energy, and others, saffire renewables plans to use nrel technology to help turn corn stover into sustainable aviation fuel.

The Arkalon Ethanol facility near Liberal, Kansas—operated by Conestoga Energy—will host a SAFFiRE Renewables’ pilot plant to produce cellulosic ethanol. Photo from Conestoga Energy

On its path to opening a facility designed to turn agriculture residue into a scalable biofuel business, SAFFiRE Renewables, LLC plans to break ground on its pilot plant near Liberal, Kansas, in late 2024.

In 2023, the company negotiated a license agreement for the National Renewable Energy Laboratory’s (NREL’s) deacetylation and mechanical refining (DMR) process, a technology seen as important for sidestepping challenges with cellulosic biofuel facilities in the past. DMR uses a “gentle” alkaline bath and a mechanical shredder to prepare corn stover for ethanol fermentation—essential steps for accessing the energy-dense sugars locked inside.

Ultimately, ethanol made at the plant, which will be operated by Conestoga Energy, can be upgraded into sustainable aviation fuel (SAF) using LanzaJet’s alcohol-to-jet technology. Estimates suggest the resulting SAF will have a carbon footprint at least 83% lower than conventional jet fuel.

According to Anthony Gregory, SAFFiRE’s chief operating officer, the planned construction of the pilot plant reflects the advantage of national laboratory–industry partnerships for enabling cornerstone technologies like DMR to make an impact in the real world.

“NREL has put in a decade of research on DMR that has been shown to not only solve many of the preexisting problems with cellulosic ethanol but also to have new advantages for processing biomass,” he explained. “Now, the lab’s research is being taken up by a commercial entity that plans to scale it and put it into production as a continuous, integrated process. It’s a great example of the different skills that the public and the private sectors can bring to the table.”

Initial funding for the plant was provided by the U.S. Department of Energy (DOE) Bioenergy Technologies Office  (BETO), with a 50% match from Southwest Airlines. Southwest has the option of purchasing SAFFiRE’s cellulosic ethanol—and the subsequent SAF—to fuel its aircraft.

“The funding award from BETO was key for launching our new technology,” said Michael Himmel, the co-principal investigator of the project. “This permitted NREL scientists and engineers to collaborate closely with industry to scale our patent-pending DMR pretreatment process.”

With a potential buyer in place, fuel credits available, and NREL’s DMR technology, SAFFiRE aims to take cellulosic ethanol to where it struggled to go in the past.

“The announcement of this pilot facility in Liberal, Kansas, is huge,” said Eric Payne, the NREL senior licensing executive who manages NREL’s DMR intellectual property. “It's the phoenix that is rising from the ashes of the now defunct second-generation ethanol industry, and that's a big deal for federal SAF goals.”

Gentle Pretreatment: How NREL DMR Sidesteps Roadblocks to Cellulosic Biofuels

NREL’s deacetylation and mechanical refining (DMR)  process combines low-severity chemical pretreatment and mechanical refining to sidestep the expenses and challenges of traditional pretreatments.

Depending on the process used to make it, biofuel made from lignocellulose—the fibrous, often cast-off parts of plants—can net deep reductions in greenhouse gas emissions compared to fossil fuels and even first-generation biofuels. According to DOE’s Alternative Fuels Data Center , for example, ethanol made from lignocellulosic corn leaves, stalks, and cobs can reduce emissions by 88% to 108% on a life-cycle basis compared to conventional jet fuel.

According to NREL scientist Nancy Dowe, however, past efforts to commercialize these “cellulosic biofuel” technologies uncovered real challenges.

“A lot of the failures of old cellulosic ethanol plants were not so much on the conversion side of things,” she explained. “It really was around material handling and pretreatment—basically opening up that plant structure for enzymes to come in and break it down into sugars.”

Old cellulosic biofuel technologies used highly specialized equipment that relied on acids, heat, and high pressures to remove impurities from the corn stover—such as acetate, lignin, and ash. While those processes were highly effective at breaking down the plant material, their extreme operating conditions created persistent headaches at industrial facilities. The acids corroded expensive equipment over time. Clogs formed as the shredded stover was fed into high-pressure reactors.

According to Gregory, those issues made it difficult to scale facilities to process thousands of tons of biomass a day.

“A commercially viable process needs to operate with very high reliability, generally running continuously at least 90%–95% of the time,” Gregory said. “When you’re pumping solids around, you want to minimize plugs and holdups.”

NREL’s DMR technology emerged to address these recognized challenges with cellulosic biofuel production. A research team—including NREL’s Dowe, Michael Himmel , Xiaowen Chen, and many others—responded by systematically reinventing biomass pretreatment with attention to past challenges.

“NREL took a step back to look at the big picture and began asking: ‘What are some of the major issues we are seeing?’” Dowe explained.

The result is a technology that uses mechanical refiners already common in the paper industry—cutting capital costs. DMR relies on noncorrosive chemicals to lower toxicity. Perhaps most importantly, it uses nonpressurized tanks that work at low temperature and pressure, rather than high-pressure reactors, making it easy to rapidly feed large volumes of biomass. Small-scale studies suggest these advances can lower capital and operating expenses and increase the efficiency and ease of making sugars fermentable to ethanol.

From Liberal, Kansas, to Soperton, Georgia: Turning Ethanol Into Sustainable Aviation Fuel

SAFFiRE expects the pilot plant to handle 10 tons of corn stover every day, which could translate to an output of roughly 0.3 million gallons of cellulosic ethanol every year. Although that is a fraction of the nearly 100 million gallons produced annually from the much larger corn ethanol facility on site, SAFFiRE plans to use the pilot plant as the first in a series of progressively larger facilities.

“Part of our strategy has been to be systematic because when it comes to new technology, you should not skip steps in scaling,” Gregory explained. “We are working to take a methodical approach to developing the technology.”

The idea, Gregory said, is to resolve technical issues and develop robust business plans, local supply chains, and relationships with suppliers and vendors. For example, SAFFiRE and Southwest are conducting in-depth analyses on the ethanol market, the SAF market, and available tax credits—aiming to smooth the pathway to build more, larger plants elsewhere across the United States in the coming decade.

For now, the plan for the pilot plant is to ship ethanol made in Liberal, Kansas, to a Georgia facility owned by LanzaJet, which uses a proprietary process to turn ethanol into SAF. In the future, that model might be replicated and scaled to respond to rapidly increasing demand for the renewable jet fuel—demand driven by state and federal biofuel incentives as well as SAF purchase agreements from large U.S. airlines, including Southwest.

According to Gregory, a successful SAFFiRE pilot plant would have resounding impacts across industries.

“I think this is good for so many different industries in the United States,” he said. “This is good for the agriculture industry. This is good for the corn ethanol industry. This is good for the airline industry, and it can create jobs that are going to be here in the U.S.”

Learn more about NREL's bioenergy and sustainable aviation research.

Empirical Tests of the Green Paradox for Climate Legislation

The Green Paradox posits that fossil fuel markets respond to changing expectations about climate legislation, which limits future consumption, by shifting consumption to the present through lower present-day prices. We demonstrate that oil futures responded negatively to daily changes in the prediction market's expectations that the Waxman-Markey bill — the US climate bill discussed in 2009-2010 — would pass. This effect is consistent across various maturities as the proposed legislation would reset the entire price and consumption path, unlike temporary supply or demand shocks that phase out over time. The bill’s passage would have increased current global oil consumption by 2-4%. Furthermore, a strengthening of climate policy, as measured by monthly variations in media salience regarding climate policy over the last four decades, and two court rulings signaling limited future fossil fuel use, were associated with negative abnormal oil future returns. Taken together, our findings confirm that restricting future fossil fuel use will accelerate current-day consumption.

We would like to thank Kyle Meng and Derek Lemoine for sharing the prediction market data and for helpful feedback, as well as participants of the Virtual Seminar on Climate Economics by the Federal Reserve Bank of San Francisco and the Harvard Seminar in Environmental Economics and Policy. The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research.

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• SAFFiRE Renewables biofuel pilot plant to be developed in Kansas

On its path to opening a facility designed to turn agriculture residue into a scalable biofuel business, SAFFiRE Renewables, LLC plans to break ground on its pilot plant near Liberal, Kansas, in late 2024.

In 2023, the company negotiated a license agreement for the National Renewable Energy Laboratory’s (NREL’s) deacetylation and mechanical refining (DMR) process, a technology seen as important for sidestepping challenges with cellulosic biofuel facilities in the past. DMR uses a “gentle” alkaline bath and a mechanical shredder to prepare corn stover for ethanol fermentation—essential steps for accessing the energy-dense sugars locked inside.

Ultimately, ethanol made at the plant, which will be operated by Conestoga Energy, can be upgraded into sustainable aviation fuel (SAF) using LanzaJet’s alcohol-to-jet technology. Estimates suggest the resulting SAF will have a carbon footprint at least 83% lower than conventional jet fuel.

According to Anthony Gregory, SAFFiRE’s chief operating officer, the planned construction of the pilot plant reflects the advantage of national laboratory–industry partnerships for enabling cornerstone technologies like DMR to make an impact in the real world.

“NREL has put in a decade of research on DMR that has been shown to not only solve many of the preexisting problems with cellulosic ethanol but also to have new advantages for processing biomass,” he explained. “Now, the lab’s research is being taken up by a commercial entity that plans to scale it and put it into production as a continuous, integrated process. It’s a great example of the different skills that the public and the private sectors can bring to the table.”

Initial funding for the plant was provided by the U.S. Department of Energy (DOE) Bioenergy Technologies Office (BETO), with a 50% match from Southwest Airlines. Southwest has the option of purchasing SAFFiRE’s cellulosic ethanol—and the subsequent SAF—to fuel its aircraft.

“The funding award from BETO was key for launching our new technology,” said Michael Himmel, the co-principal investigator of the project. “This permitted NREL scientists and engineers to collaborate closely with industry to scale our patent-pending DMR pretreatment process.”

With a potential buyer in place, fuel credits available, and NREL’s DMR technology, SAFFiRE aims to take cellulosic ethanol to where it struggled to go in the past.

“The announcement of this pilot facility in Liberal, Kansas, is huge,” said Eric Payne, the NREL senior licensing executive who manages NREL’s DMR intellectual property. “It's the phoenix that is rising from the ashes of the now defunct second-generation ethanol industry, and that's a big deal for federal SAF goals.”

GENTLE PRETREATMENT: HOW NREL DMR SIDESTEPS ROADBLOCKS TO CELLULOSIC BIOFUELS

Depending on the process used to make it, biofuel made from lignocellulose—the fibrous, often cast-off parts of plants—can net deep reductions in greenhouse gas emissions compared to fossil fuels and even first-generation biofuels. According to DOE’s Alternative Fuels Data Center, for example, ethanol made from lignocellulosic corn leaves, stalks, and cobs can reduce emissions by 88% to 108% on a life-cycle basis compared to conventional jet fuel.

According to NREL scientist Nancy Dowe, however, past efforts to commercialize these “cellulosic biofuel” technologies uncovered real challenges.

“A lot of the failures of old cellulosic ethanol plants were not so much on the conversion side of things,” she explained. “It really was around material handling and pretreatment—basically opening up that plant structure for enzymes to come in and break it down into sugars.”

Old cellulosic biofuel technologies used highly specialized equipment that relied on acids, heat, and high pressures to remove impurities from the corn stover—such as acetate, lignin, and ash. While those processes were highly effective at breaking down the plant material, their extreme operating conditions created persistent headaches at industrial facilities. The acids corroded expensive equipment over time. Clogs formed as the shredded stover was fed into high-pressure reactors.

According to Gregory, those issues made it difficult to scale facilities to process thousands of tons of biomass a day.

“A commercially viable process needs to operate with very high reliability, generally running continuously at least 90%–95% of the time,” Gregory said. “When you’re pumping solids around, you want to minimize plugs and holdups.”

NREL’s DMR technology emerged to address these recognized challenges with cellulosic biofuel production. A research team—including NREL’s Dowe, Michael Himmel, Xiaowen Chen, and many others—responded by systematically reinventing biomass pretreatment with attention to past challenges.

“NREL took a step back to look at the big picture and began asking: ‘What are some of the major issues we are seeing?’” Dowe explained.

The result is a technology that uses mechanical refiners already common in the paper industry—cutting capital costs. DMR relies on noncorrosive chemicals to lower toxicity. Perhaps most importantly, it uses nonpressurized tanks that work at low temperature and pressure, rather than high-pressure reactors, making it easy to rapidly feed large volumes of biomass. Small-scale studies suggest these advances can lower capital and operating expenses and increase the efficiency and ease of making sugars fermentable to ethanol.

SAFFiRE expects the pilot plant to handle 10 tons of corn stover every day, which could translate to an output of roughly 300,000 gallons of cellulosic ethanol every year. Although that is a fraction of the nearly 100 MMgpy produced from the much larger corn ethanol facility on site, SAFFiRE plans to use the pilot plant as the first in a series of progressively larger facilities.

“Part of our strategy has been to be systematic because when it comes to new technology, you should not skip steps in scaling,” Gregory explained. “We are working to take a methodical approach to developing the technology.”

The idea, Gregory said, is to resolve technical issues and develop robust business plans, local supply chains, and relationships with suppliers and vendors. For example, SAFFiRE and Southwest are conducting in-depth analyses on the ethanol market, the SAF market, and available tax credits—aiming to smooth the pathway to build more, larger plants elsewhere across the U.S. in the coming decade.

For now, the plan for the pilot plant is to ship ethanol made in Liberal, Kansas, to a Georgia facility owned by LanzaJet, which uses a proprietary process to turn ethanol into SAF. In the future, that model might be replicated and scaled to respond to rapidly increasing demand for the renewable jet fuel—demand driven by state and federal biofuel incentives as well as SAF purchase agreements from large U.S. airlines, including Southwest.

According to Gregory, a successful SAFFiRE pilot plant would have resounding impacts across industries.

“I think this is good for so many different industries in the United States,” he said. “This is good for the agriculture industry. This is good for the corn ethanol industry. This is good for the airline industry, and it can create jobs that are going to be here in the U.S.”

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Reshoring, Automation, and Labor Markets Under Trade Uncertainty

Hamid Firooz

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2024-16 | May 8, 2024

We study the implications of trade uncertainty for reshoring, automation, and U.S. labor markets. Rising trade uncertainty creates incentive for firms to reduce exposures to foreign suppliers by moving production and distribution processes to domestic producers. However, we argue that reshoring does not necessarily bring jobs back to the home country or boost domestic wages, especially when firms have access to labor-substituting technologies such as automation. Automation improves labor productivity and facilitates reshoring, but it can also displace jobs. Furthermore, automation poses a threat that weakens the bargaining power of low-skilled workers in wage negotiations, depressing their wages and raising the skill premium and wage inequality. The model predictions are in line with industry-level empirical evidence.

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Coles introduces recyclable paper packaging for mandarins.

Australian supermarket chain Coles has introduced a new recyclable paper packaging solution for its mandarin oranges, replacing the traditionally used plastic net bags.

The transition to this new packaging is set to prevent the usage of 11,700kg of plastic annually.

The paper bags are designed to be recycled kerbside domestically.

The supermarket chain anticipates selling more than one million of these paper bags from April to October 2024.

Coles fresh produce general manager Charlotte Gilbert said: "We know how much our customers love mandarins at this time of year, so we’re pleased to be able to offer them in a new paper bag that can be put in your recycling bin once you’ve had a chance to enjoy them.

“Customers can still purchase their favourite mandarin loose, including the delicious Imperial and Afourer varieties, with more than 16 million tonnes of the citrus fruit expected to be sold across Coles stores this season.”

The new 800g paper bags are available across all states and territories in the country, except Western Australia, with prices starting from A$5.50 ($3.61).

In response to the launch, Australia-based environmental organisation Planet Ark's CEO Rebecca Gilling said: "It’s very positive to see Coles designing packaging to avoid plastic waste and provide Aussies with a recyclable alternative to a plastic net bag.

“While we support buying loose and reusing bags where possible, we commend Coles for its work to close the recycling loop and provide customers with products that can be easily recycled."

In September last year, Coles started offering a free certified compostable bags option in the fruit and vegetable section across all its stores in South Australia.

"Coles introduces recyclable paper packaging for mandarins" was originally created and published by Packaging Gateway , a GlobalData owned brand.

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