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Thứ Hai, ngày 11 tháng 4 năm 2011

Recent developments in the world of biofuels: Spring 2011

CROPS FOR BIOFUEL to follow up Biofuel information exchange : Jatropha remains a hot topic in the scientific community and we start this review of recently published papers with an update on Jatropha around the globe. Then, because of a number of recent reviews on their future, we look at algal biofuels, which are seen by many as the biofuel panacea, despite the technical issues in production that still dominate the field. We then finish with some new biomass papers which, in common with oil from algae, emphasize the need for novel scientific solutions in the production processes, to enable them to achieve commercial viability.

Jatropha
The Indian experiment
A paper by Das & Priess1 (2010) reviews progress on this crop in India and reminds us that a major aim of the Indian National Mission on Biofuels (back in 2003) was to realize the potential yields of oilseeds under different biophysical conditions and to assess their performance on degraded lands. This mission focused on the use of non-edible oils as a source of biodiesel, primarily from jatropha. Meticulous planning was exhibited in the outline of the programme, which had foreseen a testing phase (2003–2007) and a subsequent self sustaining production phase (2007–2012). Targets were made for what has turned out to be an optimistic 20% blending of biodiesel by 2011–2012. Research projects were initiated with more than 35 participating institutions, aiming at studying a multitude of aspects of oilseed-based biodiesel production (such as plant physiology, oil content variability, development of high oil yielding varieties, improved oil extraction technologies, efficient industrial processes, economic viability, and developing market mechanisms). However, despite all this planning, the authors report that the “level of uncertainty has neither been eliminated nor diminished in the last seven years” with the same questions the Mission posed in 2003 still extant today.

Conflict and competition
Indeed in the most recently published field-based study2 of the agronomic and economic viability of jatropha plantations on private farms from Tamil Nadu (India), we find jatropha yields much lower than expected and unprofitable. Future viability is also strongly compromised by water access say the authors. On the whole, they conclude, the crop impoverishes farmers, particularly the poorer and socially backward ones. The highest yield in 3-year old plantations in rain-fed conditions was only 450 kg seed/ha compared to 750 kg/ha for irrigated conditions. This is but a fraction of estimated yields from those who boosted jatropha only a few years ago. The authors do not mince their words: jatropha cultivation “not only fails to alleviate poverty, but its aggressive and misguided promotion will generate conflict between the state and the farmers, between different socio-economic classes and even within households. The water demands of the crop can potentially exacerbate the conflicts and competition over water access in Tamil Nadu villages.”

Coincidentally, another paper from India, from the New Delhi based National Council of Applied Economic Research3 also raises the spectre of conflict over jatropha. The purpose of the study was to find out whether Indian jatropha could meet its 20% blending target by 2020 and lists estimates of wastelands for jatropha production including as fencing boundaries of crop fields and public lands along the railway tracks, canals, etc. In theory say the authors, India has sufficient land to meet biodiesel requirements without hampering normal agricultural production.

They question however whether this land is really available for jatropha since they are already occupied or are being used by millions of landless families, marginal farmers and floating population in the rural areas. Most of these lands would be occupied by these marginal people for their livelihood, often for cattle husbandry which would compete with jatropha cultivation and remove the only source of livelihood of this section of people. It would not be easy, say the authors, for governments to acquire these lands and transfer to the agencies, persons interested in cultivating jatropha. Taking away lands from them would encounter stiff resistance in many states and thus would not be politically feasible.

Yield issues in China
In Southern China, Cheng-yuan Yang and co-workers4 report that jatropha seeds were collected from 80 locations across the region and planted in a germplasm resource garden to study their biological characteristics and agricultural properties. Among the 80 sources, six with higher oil yield and better expression of phenotype were selected for a small-scale trial, conducted to determine oil yield. From these tests, a maximum value of 783 oil kg/hectare was recorded. The authors note that this amount is a somewhat surprising 2.7 times more than what Chinese jatropha farmers achieve for 3-year-old trees. These latter figures seem to be dramatically low and are further testament to the major yield problems faced by those trying to make this crop a commercial success. Small wonder therefore that scientists are turning to genetic engineering. For example, also in China, Jingli Pan et al. (2010)5 report some early advances in genetic engineering of jatropha through developing an Agrobacterium-mediated transformation protocol using cotyledon explants from jatropha seeds.

Land use effects in Brazil
Meanwhile In Brazil, Bailis & Baka (2010)6 analyse the greenhouse gas (GHG) emissions from synthetic paraffinic kerosene (SPK) produced from jatropha as a jet fuel substitute. The authors calculate that for a 20-year plantation life-cycle with no direct land use change (dLUC), use of jatropha could cut GHG emissions by 55% relative to conventional jet fuel. When dLUC is factored in however, widely varying scenarios result, ranging from an 85% decrease from the reference scenario when planted on former pastoral lands, to a 60% increase when planted on cerrado woodlands.

The African jatropha situation
Jatropha features prominently in a study of biofuel developments in Mozambique by Schut et al. (2010)7 for Directorate-General for International Cooperation (DIGIS) of The Netherlands. The paper and the report they made for DGIS8 are a mine of useful statistics on biofuels in Mozambique. Their report covered pipeline biodiesel projects of US$298 million and bioethanol projects US$1003 million. Average investment per hectare shows that sugarcane production is far more capital intensive than producing jatropha, mainly driven by higher planting density, and costly investments in irrigation systems and ethanol distilleries. The potential employment per hectare for the whole biofuel sector, was estimated to be between 0.14 and 0.17 jobs per ha. The 12 biodiesel projects that were examined, aimed to produce an average of 2.6 t jatropha oil/ha/year, which the authors suggest “will be extremely difficult, if not impossible.”

At the same time, the average expected yields by the three biggest sugarcane projects in Mozambique are 113 t cane /ha. But the authors point out that the best average yield for the Mozambican sugar industry over the past five years was 72 t /ha and the best average company yield over the same period was 87 t /ha. Data from the Brazilian sugarcane sector shows averages of 77.6 t /ha in 2007, so expected sugar yields look, as for jatropha, unlikely. The authors suggest that most of the ethanol produced in Mozambique will be exported to the EU.

Based on their analysis and geographical mapping, the authors conclude that biofuel developments are mainly taking place in areas near good infrastructure (roads and ports), where there is skilled labour available, and access to services and goods, processing and storage facilities. Compared to the policy objectives described in the Mozambique National Biofuel Policy and Strategy (NBPS), their analysis shows that currently few projects are located in remote, rural areas. Moreover, job creation as proposed by investors seems lower than expected by the government in the NBPS. Nonetheless, although the currently operational biofuel projects are not in the most remote rural areas, they do contribute to socio-economic development by generating employment, income and more indirect local spin-offs.

A similar study by Habib-Mintz (2010)9 was carried out in Tanzania which like Mozambique has become a major attraction for biofuel companies for its vast, apparently unused land. The author conducted fieldwork in 2008 to examine jatropha as the major feedstock of the Tanzanian biodiesel production experience. Although the government plans to produce biofuels for national usage, until the country sets up national targets and a grid feed-in system, producing companies are concentrating on exports. Two biofuel companies were the main focus for this study: Sun Biofuels (engaged in 11 villages in Kisarawe since 2006, occupying 9000 ha of land); and East Africa Biodiesel (EABD) (with 6000 ha of land from six villages the in Bahi district since 2008). Amongst other things, the author looked at the proposed benefits of the schemes for local people and found some surprisingly high estimates. For instance: for 6000 ha of jatropha, EABD claims to be able to employ 606,000 people, which seems extremely optimistic compared with the situation in Mozambique described above. In this study, the author refers back to repeated failures to profit from cash crops in past decades in Tanzania. This is seen as a fundamental weakness in the agricultural sector; namely an incomplete land tenure system, incomplete decentralization, inefficient infrastructures, and poor connectivity with the rural areas. These structural limitations, she says, hinder land utilization and reduce marginal returns. All of which then translate into prolonged poverty, food insecurity, and loss of human and social capital.

Finally in Kenya, Hunsberger10 reports farmers’ perceptions about growing the new crop of jatropha. Farmers expressed high hopes for what the new crop would bring them. The majority expected to use the oil for household purposes (lighting and/or cooking) as well as to sell either seeds or oil products for cash. Their specific goals were ambitious. One farmer said he was waiting for jatropha to provide enough income that he could buy a motorbike and a solar panel – both major purchases. One woman hoped it would support her in her old age so that she would no longer have to cultivate more labour-intensive crops, explaining, ‘I am old and I don’t have the energy to look after things like maize. Jatropha is less work’. Several described their plans to use jatropha oil for lighting to save the expense of buying kerosene. Their spirit of overall optimism was captured by one farmer’s statement that ‘this plant can change lives.’ Four farmers mentioned environmental benefits that they hoped would come from planting jatropha, using phrases such as ‘it will purify the air’ or ‘it enriches the soil’. Others explicitly talked about climate change, for example, [jatropha] helps with climate change . . . Trees have been cut all around. The rains are no longer coming as they used to. I hope and believe that Jatropha will clean the air – it will fight with the smoke emitted by factories’.

Hunsberger’s study is important because it provides an opportunity to hear the authentic voice of the jatropha farmer, something that is rarely heard. Alas, their expectations seem far above what the hard field evidence is now telling us from so many sources. The term ‘hype’ has become commonly associated with jatropha and from perusal of recent papers for this report and previous ones in the series, we can only conclude that the situation is extremely discouraging. In the past there has been so much investment, so many scientific studies and so much previous donor-funded emphasis on farmer-field schools and participatory research in the agriculture sector. However, we see that the progress of scientific research and development as applied in recent times to biofuels, is not improving and that poor farmers continue to remain as inadequately advised and informed as in former decades.

Algae
We look now at the burgeoning interest in algal biofuels. As Tang et al. (2010)11 remind us, the potential of microalgae has been known for over 50 years and the subject of serious research for over 20 years. The US Department of Energy’s Office of Fuels Development funded the Aquatic Species Program (ASP) program to develop renewable transportation fuels from algae from 1978 to 1996. Over the almost two decades of that programme, approximately 300 species of oil-producing algae were selected after screening, isolation and characterization efforts from over 3000 strains of algae. In spite of these efforts however, no microalgae-based processes for biofuel production have yet been developed that are commercially viable.

Algal biofuels – true or false?
A number of recent studies review prospects for this ‘third generation’ biofuel and we start with a review by Clarens & Colosi12 who look at some of the claims that have emerged as this new industry develops. They look at seven common claims:

Claim 1: algae can produce 10 to 100 times more oil per hectare than terrestrial crops. ‘False’ say the authors; the figure is probably closer to two to eight times more than rapeseed; i.e. 6 to 25 tons/ha. They assert that algal yields are fairly consistent over a range of latitudes – algal ponds near the equator would yield more than in Scandinavia because the growing season is longer, but not because of light availability. They suggest that other considerations, such as water availability and inexpensive, flat land should drive the decision on where to locate production plants.

Claim 2: algae can be made into a variety of usable energy sources other than biodiesel. ‘True’ say the authors. Lipids are not the only energy carrier that can be produced from microalgae. In fact many of the conversion processes that yield non biodiesel energy carriers are better suited for dealing with algae as a wet suspension. For example, anaerobic digestion for conversion of algae biomass into methane gas is a well-documented possibility. Algal biomass can also be dried using a combination of mechanical and thermal processes to produce something akin to algal coal that could be co-fired with coal in conventional power plants for somewhat more ‘carbon neutral’ electricity.

Claim 3: algae have significant land-use benefits over terrestrial crops. ‘True’: the authors say that production of transportation energy from algae requires a third to a fifth of the land than liquid biofuels from terrestrial crops demands. However more must be done to validate current claims about algal cultivation on marginal lands, for example that such facilities would be deployed on lands that would otherwise serve as wildlife habitat.

Claim 4: engineered photobioreactors (PBRs) are suitable for widespread energy production from algae at field scale. ‘Maybe’ say the authors: technical evidence supporting the use of PBRs as a means to grow algae is compelling, with reported yields many times higher than achievable in conventional open ponds. However PBRs’ initial costs and environmental impacts associated with construction of the systems at field scale may well make them economically and environmentally unsustainable relative to open ponds. Algae-to-energy advocates ‘should think more like farmers and less like engineers’ suggest the authors.

Claim 5: algae sequester carbon dioxide much more efficiently than terrestrial crops. ‘False’: plants take up CO2 at roughly the same rate that they produce biomass. Real carbon sequestration implies that CO2 will be kept out of the atmosphere for some long time horizon; for example, centuries or millennia. By contrast, most of the studies undertaken to date assume that all or part of the algae biomass is ultimately combusted, releasing nearly all of the photosynthesis-fixed CO2 back into the atmosphere. Algae conversion technologies are still too unproven to say anything definitive about how much CO2 could be permanently kept out of the atmosphere. Advocates for algae-to-energy point out that algal facilities could be co-located with power plants to harness flue gases, but flue gas streams are hot, corrosive and large scale. Designing algae ponds that will harness these flue gas streams without becoming extremely acidic or over-heating the algae is a challenge.

Claim 6: industrial-scale algae production requires technological developments in several strategic areas. ‘True’: modelling has shown that large-scale algal cultivation as it is commonly envisioned (e.g., in large ponds using virgin fertilizers and CO2) would have significant environmental impacts. These would comprise significantly higher CO2 emissions, energy use and water use than benchmark terrestrial crops. The environmental burden of algae arises primarily from two factors; the use of polluting nutrients and energy-intensive separations and drying operations.

Claim 7: a biotechnology breakthrough could fundamentally alter the algae landscape. ‘True’: the authors cite the work by the ExxonMobil partnership with Craig Venter’s Synthetic Genomics Inc. to explore how algae synthesize and excrete lipids. ExxonMobil’s desire to pursue these investigations makes good sense only insofar as their engineers believe that algae are both scalable and compatible with their existing refining infrastructure. A glimpse of this comes from Subhadra & Edwards (2010)13 who give an enthusiastic account of the level of activity, innovation and investment currently happening the US on algal biofuels.

A view from Europe
Another review by Wijffels & Barbosa14 covers similar ground. They are up-beat about the chances of developing algal biofuels but emphasize that economically feasible production will only be achieved if combined with co-production of bulk chemicals, food, and feed as by-products from algae after the oil has been extracted. Research is needed to explore mild cell disruption, extraction, and separation technologies that retain the functionality of the different cell components (e.g., proteins, carbohydrates, omega-3 fatty acids, pigments, and vitamins). The algal biomass that could theoretically supply 0.4 billion m3 of biodiesel (Europe’s annual biodiesel requirement) consists of 40% protein; thus, the total by-product protein would exceed 0.3 billion tons. This is about 40 times as much as the amount of soy protein (18 million tons of soy beans with ~40% of proteins in 2008) presently imported into Europe. The authors believe that 10 to 15 years is a reasonable projection for the development of a sustainable and economically viable process for the commercial production of biofuels from algal biomass. A possible downside, the authors mention in passing, is that the area required to produce Europe’s future biodiesel requirement is roughly equivalent to the size of Portugal.

Cross-sector and integrated approaches
Another review finds yet more challenges: Greenwell et al. (2010)15 look at the nature of algal biofuel projects and conclude that a cross sector approach is required, with aquaculturists working with reactor manufacturers, biologists, engineers and chemists. Much remains to be done on the basic biology of microalgae, species selection, genetic manipulation and molecular characterization of the metabolic switch for carbon sequestering and storage. The chemistry of biofuel synthesis requires further investigation too. Although we know a lot about the upgrading of vegetable/algal oils, this has mainly been using model compounds, such as stearic acid and its esters, rather than actual algal oil. Additionally, for decarboxylation and trans-esterification upgrading, it is usually only the relatively short-chain-length aliphatic acids that were used—a comparatively small component of the total algal oils. Further investigation of catalytic decarboxylation and trans-esterification of specific algal oils or biomass is needed. Furthermore, a more efficient conversion route with innovative use of by-products could prove to reduce the overall cost of the algal biofuels production system.

Singh & Olsen (2011)16 also review algal biofuel prospects. They look at bio-diesel, -gas, -ethanol, -hydgrogen, algal gasification and sustainability issues. They too conclude that significant improvements in the efficiency, cost structure and scalability of algal growth, lipid extraction, and biofuel production must be made to be commercially viable. For this purpose a defined set of technology breakthroughs will be required to develop the optimum utilization of algal biomass for the commercial production of biofuel. Subhadra (2010)17 agrees and takes this further to propose a visionary integrated renewable energy park (IREP) approach, to amalgamate various renewable energy industries established in different locations. This, says Subhadra, would aid in synergistic and efficient electricity and liquid biofuel production with zero net carbon emissions while avoiding numerous sustainability issues such as productive usage of agricultural land, water, and fossil fuel usage. The author admits that there are significant economic and policy barriers that need to be addressed to maximize the success of this integrated approach to clean energy, and it would seem that this would need a substantial and lasting commitment from public funds for a technology that is still far from being proven.

The economics
Gallagher (2011)18 demonstrates the huge returns possible from algal biofuels if real crude oil prices were to rise significantly above $100 per barrel and keep rising at a strong rate. If these conditions are encountered, his economic analysis shows an increasing insensitivity to loss of subsidies and increases in capital and/or operating costs. In other words, if “Peak Oil” and decline become a reality, biodiesel produced from algae appears extremely attractive as crude oil and conventional diesel prices sharply escalate, even if the assumed capital and operating costs prove to be optimistic.

A sea view
A completely different approach is suggested by Thomsen (2010)19 who suggests that only 0.4% of global water is fresh water which will increasingly be a limiting factor. Instead he points to the 98% of all the water on this planet that is seawater and suggests that it is time to start using it. Bioreactor microalgae can be mixed with marine algae harvested from the sea to achieve a blend with the desired characteristics to be used by conventional biomass power plants. Harvesting marine algae from the ocean has been trialled, and can be carried out in an ecological suitable matter. Remote sensing and modelling of surface currents is used to find the suitable harvesting sites.

Algae get sick too
A new paper on algal diseases by Gachon et al. (2010)20 adds a new twist that perhaps has been hitherto neglected. The authors suggest that the expanding use of open systems for the mass culture of microalgae for biofuels will also inevitably favour disease outbreaks and anticipate that epidemics will become a significant issue for this sector over the coming years. The authors review the great diversity of algal pathogens. The best known pathogens of algae are viruses, subject to intense studies over the last three decades, since their ecological role was first appreciated. Algae are also plagued by a variety of even lesser known, but arguably equally important bacterial and eukaryotic pathogens. Bacterial pathogens (mostly Gram-negative taxa such as Alteromonas, Cytophaga, Flavobacterium, Pseudomonas, Pseudoalteromonas, Saprospira and Vibrio) mainly cause rot symptoms and galls on seaweeds.

Shell calls it a day on algae
From the many studies recently published, there is no doubt that an enormous amount of work still needs to be done to make algal biofuels an economic reality. Singh et al. (2011)21 estimated that it currently costs €50/L algal derived oil. This means that more than an order of magnitude improvement is required to make algal derived oil viable, which inevitably is going to take a long time to acheive. So off-putting are the hurdles that Shell Oil recently announced they are pulling out of algal oil development whilst retaining investment in more conventional ethanol (first generation) and biomass (second generation) options.22

Can the science be more user-friendly?
As we mention above in the case of jatropha, a question that emerges is whether the current way that science is done and reported is adequate for the immense effort that is required. To determine whether algae are a viable source for renewable diesel, Beal et al. (2010)23 suggest that three questions must be answered are (1) how much renewable diesel can be produced from algae, (2) what is the financial cost of production, and (3) what is the energy ratio of production?

To help accurately answer these questions, the authors then propose a detailed and logical analytical framework and associated nomenclature system for characterizing renewable diesel production from algae. This framework consists of three principles: using well-defined metrics, using symbolic representation for unknown information (i.e. areas where additional data are needed are identified in standard notation), and presenting results that are consistent and include all relevant information. The authors provide examples of the confusing and partial reporting of some recently published papers and call for the widespread use of common nomenclature, and a consistent reporting framework by primary researchers. This would allow systems-level analysts to integrate the results of primary research into estimates for the potential of algae for renewable diesel. In turn, widespread use of a framework by systems-level analysts would lead to improved estimates, which are valuable for researchers and policy makers.

In essence then, the authors are proposing a sort of reporting standard for researchers to adhere to. This is a very welcome development, because the great majority of biofuel research to date (not only algal biofuels) has lacked sufficiently clear and unambiguous data from which to make accurate assessments about their true value. This is particularly important when so much public money is being placed in biofuels subsidies which some feel will never be repaid in terms of slowing the transport industry’s growing contribution to climate change.

Biomass
Featuring a new journal
We end this review with a look a developments in biomass sourced biofuels. To start, we draw the readers’ attention to an excellent series of biofuel reviews that appear in a new journal published by Future Science Ltd., called ‘Biofuels’ that started in 2010. We have already referred to some of these above, and on the subject of biomass for instance, Himmel et al. (2010)24 review in some detail and with helpful graphics, the range of microbial enzyme systems that are available for biomass conversion. Kamban & Henson (2010)25 on the other hand review the state of the art in upstream processing of cellulose for bioethanol production with bacteria, emphasizing the importance of engineering bacterial processes for efficient cellulosic bioethanol production. The authors note that although some advances have been made in the genetic engineering of plant feedstocks, research is still in its infancy and requires continuing efforts to engineer bacteria to synthesize cellulase enzymes, to ferment both pentose and hexose sugars, and to exhibit high ethanol productivities.

Webster et al. (2010)26 give a comprehensive review of the role of plant community diversity in bolstering productivity, resistance to pest and pathogen pressure and wildlife habitat, among other ecosystem services for biomass production from grasslands. Tyner (2010)27 reviews market uncertainties and government policies for cellulosic biofuels and for him the bottom line is that existing government policies do not provide the degree of reduction in uncertainty that would be needed to induce commercial investment in cellulosic biofuels. In today’s financial markets, it is even more difficult for venture capitalists to consider investments in this sector. Therefore he feels, without changes in our current approach, biofuels targets are unlikely to be achieved.

Wilkie & Evans (2010)28 analyse the possibilities of using invasive aquatic plants as a biofuel. Invasive plants almost by definition grow very fast and to make a virtue of necessity, it may be economically feasible to harvest them. Aquatic weeds tend to grow in nutrient rich waters fed by agricultural run-off, so it is possible to imagine a system that makes use of this free resource and at the same time reduces the excess level of nutrients that reduce aquatic biodiversity and that may often need to be removed before human consumption. The review therefore makes the case that invasive aquatic plants represent an untapped potential bioenergy source. The authors call for the development of harvester machines and processing infrastructure that can deliver aquatic plant biomass to refineries in a cost-efficient manner. They point to a study on water hyacinth that suggests the amount of biomass collected may already be economically justifiable.

The problem with biomass
The problem with all biomass however is that it is not a very concentrated form of energy; Singh et al. (2010)29 calculate that the energy content of a molecule from of biomass sources such as switchgrass, poplar and even sugars is only two thirds that of a molecule of gasoline. It is typical during biofuel production to lose up to a half of the carbon atoms in the biomass as carbon dioxide to meet the processing energy requirements. There is also a limit to how far you can move such material before the transport costs begin to outweigh the value of the energy collected. This therefore puts a cap on the size of the biomass energy plant and hence its efficiency.

There seems to be no way around this fundamental limitation, but Singh, Agrawal and co-workers at Purdue University have come up with an entirely novel solution. They reasoned that the collected biomass needs to be transformed on site to a more energy dense form before moving it. Their solution is a processing system based on fast hydropyrolysis, followed by catalytic hydrodeoxygenation, which they call H2Bioil. A fast-hydropyrolysis reactor rapidly heats solid biomass to about 500°C in the presence of hydrogen, breaking down the long chain biomass molecules. The oxygen in those smaller molecules reacts with the hydrogen resulting in high-energy density oil molecules. The quality of biofuel produced using H2Bioil can be two to three times the output from conventional processes they claim.

The crucial problem of course is how to make this a practical reality. The Purdue team propose to use a small-scale steam methane reformer which is a standard chemical engineering method of converting steam and methane into hydrogen and carbon monoxide (syngas). The source of the gas would come initially from natural gas, but the plan is to eventually obtain it from gasification of the biomass itself. Ultimately solar power might be used to produce the hydrogen. The new method could produce about twice as much biofuel as current technologies when hydrogen is derived from natural gas and 1.5 times the liquid fuel when hydrogen is derived from a portion of the biomass itself. A mobile version of this is apparently feasible and the team is now planning to try this out in the field to be commercially available within five years.

If this method proves successful, it would transform the potential of biomass for transport fuel, which currently needs just this sort of ‘out of the box’ thinking to turn it into a solid economic prospect that would attract the very significant funding that this will require.

References

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  2. Ariza-Montobbio, P. & Lele, S. (2010) Jatropha plantations for biodiesel in Tamil Nadu, India: Viability, livelihood trade-offs, and latent conflict. Ecological Economics 70: 189–195.
  3. Biswas, P.K., Pohit, S. & Kumar, R. (2010) Biodiesel from jatropha: Can India meet the 20% blending target? Energy Policy 38: 1477–1484.
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