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Thứ Sáu, 15 tháng 10, 2010

Recent developments in the world of biofuels: summer 2010

CROPS FOR BIOFUEL.To follow up BIOFUEL INFORMATION EXCHANGE. A recent review of no less than 67 biofuel life-cycle assessments (LCAs) was published recently in a new biofuel journal1. As Ester van der Voet and her colleagues point out, the very fact that politically determined biofuel targets have been set, has led to a major effort to show whether they might actually have a desirable effect for society. The review tries to find out what can be concluded from the studies and why and how they may differ. And differ they most certainly do: in the first place the studies do not adopt the same functional units. Some express results in terms of amount of energy contained in the fuel, others the weight of the fuel or the yield per unit area (e.g. hectare) or even a composite measure. Such differences make comparison between studies difficult and lead to major differences between them. Different allocation methods, all approved under the International Organization for Standardization (ISO) standard for LCA studies, can cause percentage improvement compared with fossil fuels to vary from negative to above 100%. 

How functional are life-cycle assessments (LCA)?

The authors point out that the system boundaries vary between studies, which reflect their different purposes. Hence some are well-to-wheel, others are well-to-tank, cradle-to-gate (where ‘gate’ means the final product less costs of delivery to the tank) and even cradle-to-grave where the whole transport system is evaluated, including the car and the road. The latter is the most complete and indeed is surely needed if society is to evaluate the full costs of our current free-wheeling life styles. But by so doing, these most comprehensive studies tend to reduce the overall differences between the biofuel feedstock involved, which is often the centre of interest.

At the heart of this is a fundamental problem: LCAs were never designed to cover wide-ranging questions of such global concern. LCAs are, by concept, a way of determining costs and impacts of a particular process. They are especially useful for firms looking to reduce costs of energy and materials for a particular supply chain, or of reducing environmental pollution; Coca-Cola and Mobil Oil were early adopters. It is easy for a company to use LCAs, because they can be reduced to a bottom line expressed in terms of money saved.

But when we come to biofuels, the whole point of which is to be an overall benefit to humanity, the boundaries become global and the uncertainties proliferate. This is covered in some detail in a new book by Giampietro & Mayumi2, who point out that when dealing with living systems, one can easily get caught in an analytical loop in which everything depends on everything else. E.g. several options may be considered to calculate the required energy input for generating the supply of energy carriers (‘energy carriers’ are gasoline, biofuel and wind power for example):
Option A: include only the energy spent on the operation by the machines used in the energy sector;
Option B: Option A plus the energy used to fabricate and maintain the machines used in the energy sector;
Option C: A+B plus the energy used to reproduce the energy sector as a whole. This requires including the infrastructure and demand of services of the energy sector;
Option D: A+B+C plus the energy used to reproduce the humans working in the energy sector. Includes the leisure time, education & assistance to their families.

It’s easy to see that for an investor in a short term project, s/he might only be interested in A and B. For a long term investor option C would be important, and for a caring government, option D would be important though the reason may not be immediately obvious. For D, in the case of a country that decides to rely mainly on biofuels, many times more people would have to become involved in the business than for a fossil fuel economy because bio-energy is less efficiently created; long-sighted politicians would need to decide if it would indeed be feasible to divert so much capital and human assets to this end rather than to another part of the economy.

So fundamental is energy to the workings of a society, say Giampietro & Mayumi, that it is not possible to isolate and compare sub-systems such as biodiesel and wind power, without considering the way society itself functions. In other words, the very nature of our society depends on the way that it finds and processes energy. The authors refer to historical examples of civilizations that got it wrong: ruling elites that were no longer able to gain wealth by conquest, would turn inwards to divert more and more internal resources for their own ends, to the point that primary producers (mainly farming communities) collapsed or rebelled. Societies that can no longer afford fossil fuels may in future do the same, and perhaps the increase in land-grabbing that we are seeing in parts of the world is an indication that this has already started3.

Van der Voet et al. conclude that some of the problems with LCA can be fixed by standardizing methodologies. However, there are other limitations with regard to large-scale long-term impacts, where other types of analysis may be more appropriate; for example, land use change as a result of biofuel policies. Aspects such as risk of competition with food crops and local and regional social consequences are outside the scope of present LCA, and they may never be able to include all relevant aspects. However, the concept of social LCAs is being developed. All decision makers should take heed of what the authors say and then read Giampietro & Mayumi’s book to help reorient their thoughts.

LCA of second generation biofuels. When reading LCA papers on the impacts of second generation biofuels, it is sometimes easy to forget that second generation biofuels are not yet commercially available. A new review by Zhu and Pan4 highlights some of the challenges that are faced to commercialise cellulosic ethanol. Despite substantial progress in cellulosic ethanol research and development they say, many problems remain to be overcome. For example, the high energy consumption for biomass pre-treatment remains a challenge. Excellent wood cellulose saccharification efficiency can be achieved using the organosolv process, sulphite pre-treatment to overcome recalcitrance of lignocellulose (SPORL), and steam explosion in the case of hardwood; however improvement in the yield of hemicellulose sugars is still needed. Scaling up the whole process is a key challenge: capital equipment required for commercial demonstrations of some technologies, such as steam explosion, does not yet exist.

Zhu and Pan point out that the pulp and paper industry has the capability and infrastructure for handling biomass on the scale of 1000 ton/day, equivalent to the scale of a future cellulosic ethanol plant of 100 million litres/year, but there is a lack of economic incentive for that industry to shift to a stand-alone biorefinery for ethanol production because fibre for paper is still worth more than ethanol.

Other problems abound: the recovery of pre-treatment chemicals and wastewater treatment are also important issues in selecting commercial production technologies. The dilute acid and acid-catalyzed steam pre-treatment can be performed without the recovery of the acid because of the low cost of sulphuric acid. However, substantial amounts of alkaline chemicals are required to neutralize the pre-treatment hydrolysate. In addition, the salt produced from the neutralization needs to be properly disposed of. Furthermore, the dissolved organics in the stream of post-fermentation pre-treatment hydrolysate represent a significant amount of chemical oxygen demands and needs to be dealt with. On the other hand, the solvent ethanol used in the organosolv process can be easily recovered through distillation, but a significant amount of energy is required using current technology.

Finally, feedstock versatility is another factor to consider. Cellulosic ethanol is a commodity product and cannot afford high-grade feedstock. It is expected that future cellulosic ethanol refineries will have very little flexibility in their choices of feedstock (having to use what is cheap and available at any point in time), therefore the pre-treatment process must be versatile. Pre-treatment processes that are only effective on certain feedstocks will have difficulties in commercial adoption. Challenges in developing integrated forest biorefineries, include how to maintain pulp yield and strength and how to concentrate and ferment the hemicellulosic sugar stream that mainly contains pentose when hardwoods are used.

A new LCA review of switchgrass5, regarded as a promising second generation biofuel, finds that with regard to global warming potential, driving with switchgrass ethanol fuels would lead to less greenhouse gas (GHG) emissions than gasoline: a 65% reduction may be achieved in the case of E85 ethanol fuel. But apart from that, switchgrass would not offer environmental benefits in the other impact categories compared to gasoline. The authors estimate that switchgrass agriculture would become a main contributor to eutrophication, acidification, and eco-toxicity – and emissions from bioethanol production would cause a greater impact in photochemical smog formation.

A further review of LCAs of biofuels from a range of sources of lignocelluloses6, looks at seven impact categories. When it comes to GHG savings, it also finds that switchgrass is the best crop, followed by sugarcane+bagasse (the fibrous residue remaining after sugarcane stalks are crushed to extract their juice), which was included as a comparison. Fuels from corn stover, flax shives and hemp hurds led to a worse performance than gasoline. Sugarcane-derived ethanol turns out to be the best option in terms of photo-chemical oxidation potential (smog) whereas switchgrass and hemp are the poorest. In the category of human and ecotoxicity potential, as well as acidification and eutrophication potential, flax-derived ethanol showed the best environmental performance among all the ethanol fuels.

The authors point out that in many impact categories (global warming potential, photochemical oxidation potential, human and eco-toxicity potential, acidification potential and eutrophication potential) ethanol fuels as a whole do not show advantages over gasoline, so they suggest that strong promotion of bioethanol as a transport fuel needs to be carefully considered. They also suggest that more advanced technologies with optimization of energy use and emissions in both agriculture and ethanol refinery still need to be developed to reduce the current relatively high scores.

The economics of CO2 missions in LCA. In their recent paper, de Gorter and Tsur7 offer a green house gas (GHG)-reduction standard for biofuel production based on a cost–benefit test that allows for a changing carbon price and a positive social discount rate (SDR). They argue that the economic consequences of CO2 emissions and uptakes associated with a biofuel policy must be based on cost–benefit analyses and the latter cannot be adequately addressed by LCA, whether it recognises indirect land use change (iLUC) or not. This is so because LCA is based on the summation of physical GHG balances (where each GHG is weighted by its global warming potential) and the comparison of aggregate emissions with aggregate uptake over a specified period of time (e.g. 30 years). Physical balances summed over many years, however, are devoid of cost–benefit significance for two reasons. First, attaching an economic value (benefit if positive or cost if negative) to a physical quantity requires the use of prices. Second, summing values that accrue at different years requires discounting. Physical GHG balances can be used in cost–benefit tests (in the sense that using them instead of genuine costs and benefits would yield the same cost–benefit criterion) only if (i) the price of carbon (i.e. the price that converts physical quantities into values) is constant over time and (ii) the SDR is zero. Both conditions are inappropriate say the authors: the price of carbon increases over time as long as atmospheric GHG concentration increases (with its ensuing climate-change-induced threats); and a positive (though not necessarily constant) discount rate is required to determine intergenerational tradeoffs when economic growth is expected to persist (even at a reduced rate). Existing biofuel GHG-reduction standards (with or without iLUC) are therefore biased and distort the ensuing policy recommendation.

The impact of the inherent variability of biofuel production systems in LCA. Chiaramonti & Recchia’s recently published paper8 also finds fault with the LCA process. They agree that LCA methodology is a principal tool for the estimation of the impact of biofuel chains and that this is also reflected in the recently issued EU Renewable Energy Directive on the promotion of the use of renewable energy. However, the results of LCAs depend heavily on the quality of the information given as input to the study. In addition, the comparison of a large number of very different aspects (technical, geographical, agronomic), as some LCAs attempt, is a very difficult task due to the extremely large number of variable conditions and parameters. Their paper looks at these problems by considering a very specific biofuel chain: the production and use of sunflower oil in North-Central Italy. Their results showed very large variations in the calculation of the CO2 equivalent emissions, depending on local agricultural practices and performances, even for such a small and well defined biofuel chain. For instance, they graph over 100 different energy input/output field measurements, and reveal an extraordinary variation – a range of ~ 6 to 46 GJ ha-1 input and ~15 to 130 GJ ha-1 output, with no significant relationship between them. They suggest that adoption of the present standardized LCA approach for generalized evaluations in the bioenergy sector should therefore be reconsidered. They recommend that LCA studies, even while addressing very specific and well defined chains, should always include the range of the estimates, since this range of variation of LCA could be significantly greater than the initially set quantitative targets and therefore compromise the whole study. The authors make suggestions for small scale projects to help develop sound but realistic processes to assess biofuel sustainability.

There are growing signs, therefore, that LCAs have a number of methodological difficulties and inconsistencies that urgently need to be addressed. An uncomfortable, but inescapable conclusion is that the systems being measured are so complex and variable, that they can all too easily be tweaked to come to almost any desired conclusion.

Impacts of using crop residues in biofuels production

A major problem of biofuels is that their overall energy gains are often low. This means that in many cases, all crop residues are collected and used to generate additional energy, as so called co-products, and are nearly always counted as such in prospective models of second generation biofuel production. A problem of LCAs is that they often don’t consider the various downsides of doing this. A new review by Blanco-Canqui9 looks specifically at these downsides. He finds that indiscriminate crop residue removal harvesting for expanded uses has adverse impacts on soil properties, water quality, soil organic carbon (SOC) sequestration, and crop production particularly in erodible and sloping soils. Alternatively, he found that growing perennial warm-season grasses (WSGs) and short-rotation woody crops (SRWCs) show promise to provide a range of ecosystem services over crop residue removal. Short-rotation woody crops sequester SOC, reduce soil erosion, improve soil properties, and promote wildlife habitat.

The authors suggest that the benefits of WSGs and SRWCs are greater when grown in marginal, degraded, and abandoned lands than when grown in prime agricultural lands. WSGs and SRWCs as biofuels would have to be carefully managed under such conditions however, to achieve the desired ancillary soil and environmental benefits. Development of sustainable systems of WSGs and SRWCs in marginal lands is a therefore a high priority say the authors.

An agro-ecological approach to second generation biofuel production

As if to reaffirm this point, a new paper by DeHaan et al. 10 reports detailed long-term studies of a field production system for a future grass-based lignocellulosic biofuel. There are two basic approaches to using grasses as biofuels: high input monocultures, or low input high-diversity grassland. The former is potentially easier to develop as a high yielding system, where high yielding strains can be continuously improved and deployed over time to give predictable performance. However, the latter scheme has many advantages since, low inputs decrease costs and pollution caused by those inputs, and there is an increase in biodiversity.

The authors looked at the relative yields from 168 plots in Minnesota where they varied the number of indigenous grass species. For some treatments they also included some leguminous species. Overall they found that the greater the number of grass species used (up to 16), the greater the yield, but the range of variation in yield was very high. Plots with legumes and grasses performed the best. Motivated by a desire to make future practical recommendations to farmers, they then calculated the minimum species number necessary for the system to have predictably high yields. They estimated that combinations of just one grass and the best performing legume (Lupinus perrenis) gave a performance as good as high diversity grass plots.

In practice, such ‘bi-cultures’ of one grass and legume species could be arranged so that the legume species is evenly distributed within a field, or the legumes could be grown in patches, fed to livestock, and the manure used to fertilize the grasses. With a sustained effort to breed and develop legume/C4 grass bi-cultures, plant breeders and agronomists might develop systems that are increasingly productive and mostly free from dependence on nitrogen fertilizers.

Clearly this is not a high diversity solution so the authors suggest an intriguing compromise. One strategy would be to develop numerous lower diversity systems and deploy them in a patchwork arrangement to achieve landscape-level diversity. Or, farmers could be paid to add noneconomic species to their fields solely to increase biodiversity. The authors also assert that this is not the final word: further research might show that the addition of other selected species to improved bi-cultures could increase their yields and the stability of these yields. This paper is therefore a very encouraging blend of agro-ecological theory, field experimentation and commercial awareness that many other researchers could learn from.

Jatropha update

We have just received a useful review of the present status of jatropha cultivation in Mexico and Central America11. This is the centre of origin of the plant and one of the first jatropha projects was started in Nicaragua in 1990, though it was abandoned in 1999. In this short review, Cifuentes & Fallot report that about 7,400 ha are currently under cultivation in seven countries of the region. The authors affirm the interest in jatropha throughout the region but point to the need to develop better regulatory frameworks and value chains in order to attract proper finance. Most of the projects they identify are no more than three years old and they suggest that much better dissemination of the data from these projects is required to show that the predicted yields are in fact achievable. Selection of varieties and development of technological packages appropriate to each country are also need, they suggest.

The need for better data from projects is a common deficiency and one that a recent report by GTZ tackles with some vigour12. It looks at the economics of jatropha growing for smallholders in Kenya and its conclusions are uncompromising:

‘The results of this survey, taken from interviews with hundreds of Jatropha farmers throughout Kenya, show extremely low yields and generally uneconomical costs of production. Based on our findings, Jatropha currently does not appear to be economically viable for smallholder farming when grown either within a monoculture or intercrop plantation model.

The only model for growing Jatropha that makes economic sense for smallholders, according to actual experiences in the field so far; this is growing it as a natural or live fence with very few inputs. Of course, this is precisely how Jatropha has been grown in this part of the world since it was introduced centuries ago.

Therefore, we recommend that the all stakeholders carefully re-evaluate their current activities promoting Jatropha as a promising bioenergy feedstock. We also suggest that all public and private sector actors for the time being cease promoting the crop among smallholder farmers for any plantation other than as a fence.

Although these conclusions provide a sobering retort to some of the unbridled hype that has swirled around Jatropha over the past few years, current research and development may lead to improved varieties. What is clear from the results of this field survey, however, is that that day has not yet arrived.’

The GTZ study uses the word ‘hype’ to describe the interest in jatropha and coincidentally the same word is also employed in another recent review of jatropha by Achten et al13. They write that ‘Popular claims on drought tolerance, low nutrient requirement, pest and disease resistance and high yields have triggered a jatropha hype with sky-high expectations on simultaneous wasteland reclamation, fuel production, poverty reduction and large returns on investments.’ Many of these claims are yet to be supported by scientific evidence, the authors conclude. They point to major knowledge gaps concerning basic ecological and agronomic properties (growth conditions, input responsiveness of biomass production, seed yield and the species’ genetics), that make seed yield poorly predictable. Considering the current expansion, this situation might hold considerable sustainability risks (economic, social and environmental). Among other issues, the water requirement and water footprint of jatropha are still poorly understood. A better knowledge of these agronomic properties is vital for the further application of the species. Jatropha should therefore still be considered a (semi-) wild, undomesticated plant showing considerable performance variability.

The authors highlight some potential breeding problems with this poisonous bush that might account for its notoriously variable yield: jatropha can set seed after both insect and self-pollination. However, self-pollinated fruits are lighter in general and abort before maturation in 25% of cases. It has been suggested that this could be due to early acting inbreeding depression and thus may reflect a high natural out-crossing rate. Preliminary studies indicate very low variation in microsatellite simple sequence repeat (SSR) markers within populations even of Mexican Jatropha. This is surprising since Mexico is the purported centre of origin of the species, and hence where you would expect genetically diverse populations to be found.

The authors point out that understanding the breeding pattern is central for design of domestication strategies. Breeding, large-scale mass propagation and distribution across landscapes will be much easier if the species is reproduced by natural selfing without inbreeding depression or, especially, if it reproduces by apomixis (asexual reproduction without fertilization). Given the successive introductions of jatropha and its ability of clonal mass propagation within a short time, it is possible that all African and/or Asian populations result from a narrow germplasm origin. Recent studies based on genetic markers uncovered surprisingly low levels of genetic diversity in jatropha landraces from China for instance. The authors suggest that, given the low genomic diversity in landraces, ‘smart’ out-crossing between superior Asian individuals with new introductions from the Americas should be performed. Such crosses should release any inbreeding depression and thereby increase vigour and fruit production if genetic diversity of American landraces is effectively larger.

The authors detail a number of steps that are needed to develop a breeding programme that might lead to reliable heavy yielding tree stocks. We recommend all those working on jatropha to read the paper and the GTZ report as two detailed and well argued contributions to the growing literature on this plant.

Jatropha mosaic disease
A paper by Gao et al. 14, reports the completion of the nucleotide sequence of the jatropha mosaic disease, which has emerged recently and now widely spread in India. Phylogenetic analysis of the virus genome suggests it is a new strain of Indian cassava mosaic virus. It is always unfortunate to have a single disease that affects two different crops, since this tends to make control of both more difficult. However, the authors suggest that with the genome sequenced information and the availability of the two infectious clones, it may be possible to use double-stranded hairpin RNA or artificial miRNA-mediated RNA interfering technology to generate transgenic Jatropha lines that are resistant to this new disease.

Microbial contamination of biofuels

Although it probably shouldn’t, it comes as a surprise to discover the amount of bacterial contaminants in the bioethanol industry. A new paper by Muthaiyan and Ricke15 reveals that in the process of scaling up ethanol production, bacterial contamination is becoming one of the more challenging problems facing the industry. The management of contaminants is often achieved in the bioethanol industry by using antibiotics such as penicillin G, streptomycin, tetracycline, virginiamycin, and monensin or mixtures of these compounds. Currently, penicillin and virginiamycin are commercially sold to treat bacterial infections of fuel ethanol fermentations, and some facilities use these antibiotics prophylactically. Of the antibiotics available, virginiamycin is considered one of the better choices for treatment since this antibiotic, unlike penicillin, retains its activity at lower pH values.

The authors question the concept of antibiotics use in an industrial process because of the considerable cost of adding large quantities of antibiotics and the rapid emergence of antibiotic resistance among the contaminant bacteria. This scenario represents potential public health consequences and therefore requires more research on the impacts of the bulk usage of antibiotics in bioethanol fermentation on antibiotic resistance in public health system. To avoid such a public health consequence consideration of better strategies by alternative means to control contaminants and much earlier detection of initial contamination long before drastic measures such as complete shutdown of the fermenter are required.

This paper therefore again reminds us of the ineluctable complexity of biofuel production: unlike gasoline which has rather few microbial contaminants, biofuels will always be more susceptible because there are many co-evolved organisms in the environment that will attack them and any method to control them will expend yet more energy on systems that struggle to achieve efficiency. It shows yet again that LCAs, which as far as we know never consider future problems of microbial contamination, are an imperfect tool to fully evaluate the utility of biofuels and the broader implications for society.

van der Voet, E., Lifset, R.J. & Luo, L. (2010) Life-cycle assessment of biofuels, convergence and divergence. Biofuels 1(3): 435–449.
Giampietro, M. & Mayumi, K. (2009) The Biofuel Delusion. Earthscan, London. 318pp.
Africa: up for grabs. The scale and impact of land grabbing for agrofuels (August 2010). Report Friends of the Earth Africa and Friends of the Earth Europe. http://www.foeeurope.org/agrofuels/FoEE_Africa_up_for_grabs_2010.pdf.
Zhu, J.Y. & Pan X.J. (2010) Woody biomass pretreatment for cellulosic ethanol production: Technology and energy consumption evaluation. Bioresource Technology. 101: 4992–5002
Bai, Y., Luo, L. & van der Voet, E. (2010) Life cycle assessment of switchgrass-derived ethanol as transport fuel. International Journal of Life Cycle Assessment. 15: 468–477.
Luo, L., Voet, E. & Huppes, G. (2010) Energy and Environmental Performance of Bioethanol from Different Lignocelluloses. International Journal of Chemical Engineering. 2010: 12pp.
de Gorter, H. & Tsur, Y. (2010) Cost–benefit tests for GHG emissions from biofuel production. European Review of Agricultural Economics. 37: 133–145.
Chiaramonti, D. & Recchia, L. (2010) Is life cycle assessment (LCA) a suitable method for quantitative CO2 saving estimations? The impact of field input on the LCA results for a pure vegetable oil chain. Biomass & Bioenergy. 34(5): 787-797.
Blanco-Canqui, H. (2010) Energy Crops and Their Implications on Soil and Environment. Agronomy Journal. 102(2): 403-419.
DeHaan, L.R., Weisberg, S., Tilman, D. & Fornar, D. (2010) Agricultural and biofuel implications of a species diversity experiment with native perennial grassland plants. Agriculture, Ecosystems and Environment. 137: 33–38.
Cifuentes-Jara, M. & Fallot, A. (2009) Jatropha curcas como biocombustible: estado actual del cultivo en Mesoamérica. Recursos Naturales y Ambiente. 56-57: 165-169.
Jatropha Reality Check. A field assessment of the agronomic and economic viability of Jatropha and other oilseed crops in Kenya. http://www.worldagroforestry.org/downloads/publications/PDFs/B16599.PDF.
Wouter, M.J., Achten, W.M.J., Nielsen, L.R., Aerts, R., Lengkeek, A.G., Kjær, E.D., Trabucco, A., Hansen, J.K., Maes, W.H., Graudal, L., Akinnifesi, F.K. & Muys, B. (2010) Towards domestication of Jatropha curcas. Biofuels. 1(1): 91–107.
Gao, S.Q., Qu, J., Chua, N.H. & Ye, J. (2010) A new strain of Indian cassava mosaic virus causes a mosaic disease in the biodiesel crop Jatropha curcas. Archives of Virology. 155: 607–612.
Muthaiyan, A. & Ricke, S.C. (2010) Current perspectives on detection of microbial contamination in bioethanol fermentors. Bioresource Technology,. 101: 5033–5042.

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