Biofuels are often almost universally regarded by governments as a low carbon energy source, but whether biofuels offer carbon savings depends on how they are produced. Converting rainforests, peatlands, savannahs, or grasslands to produce food crop-based biofuels in has been-I demonstrated in a recent studies to produce a net "biofuel carbon debt". A recent paper by-I private conservation group The Nature Conservancy, found that conversion of peatland rainforests for oil palm plantations incurs an overall "carbon debt" of 423 years in Indonesia and Malaysia, while the carbon emission from clearing Amazon rainforest for soybeans takes 319 years of-I renewable soy biodiesel, before the land can begin to lower greenhouse gas levels and mitigate-I global warming. (See fig 1). In contrast, biofuels made from waste biomass or from biomass grown on degraded and abandoned agricultural lands planted with perennials incur little or no carbon-I debt and can offer immediate and sustained GHG advantages. (Fargione, et al 2008).
Fig. 1. Source: Land Clearing and the Biofuel Carbon Debt, Science 29 February 2008
Nonetheless despite debate still continuing regarding the environmental benefits of a large scale switch to the use of biofuels, projections indicate a rapidly increasing trend in their adoption, particularly by those governments engaged in a strategic pursuit of energy selfâ€sufficiency. (See fig.2)
Fig. 2
Fig. 2
There are of course many benefits to national governments and concerned citizens in pursuing biofuel production The main practical benefit of using biofuels is that within some volume- constraints they~ can be integrated with fossil fuels and used within existing energy systems, such as car and lorry engines, and due to extensive government subsidies they may save the user money in the process. Moreover although the initial picture of the carbon debt incurred by many biofuel-production~ processes might seem a little bleak, the good news is that governments are increasingly choosing to be more discerning in their funding of appropriate biofuel technologies.
Secondâ€generation biofuels for example, are produced from sustainable feedstock. Sustainability of a feedstock is defined, among other factors, by availability of the feedstock, impact on greenhouse gas emissions, and impact on biodiversity and land use. Cellulosic ethanol production uses nonâ€food crops or inedible waste products and does not divert food away from the animal or human food~ chain. Lignocellulose is the "woody" structural material of plants. This feedstock is abundant and diverse, and in some cases (like citrus peels or sawdust) it is in itself a significant-I disposal problem. Second generation biofuel technologies must therefore take in to consideration that net short term energy yield alone, cannot be the only consideration. As Table 1 shows sugar cane provides a very high overall energy yield, but it would clearly be very unwise (and impractical) to turn large swathes of land currently employed for food production or for other purposes, over to the exclusive production of sugar cane.
Table 1: Composition and yields of different feedstocks (based on dry mass)
Residue
/crop ratio
Crop Dry matter
Lignin
(%)
Carbohydrat es (%)
Biofuel yield
(L kg-1 of dry
Yield
(kg/ha)
Biofuel yield lt/
(%)
biomass)
ha
Barley straw
1.2
88.7
9.0
70.0
0.31
1,184
367
Corn stover
1.0
86.2
18.7
58.3
0.29
1,734
503
Rice straw
1.4
88.6
7.1
49.3
0.28
1,399
392
Sorghum straw
1.3
89.0
15.0
61.0
0.27
736
199
Wheat straw
1.3
89.1
16.0
54.0
0.29
1,413
410
Sugarcane bagasse
0.6
26.0
14.5
67.2
0.28
11,188
3,1
Source: NRC (1958), EIA (2001), Kim and Dale (2004), and US DOE (2008a). Table showing the energy yield of several common biofuel crops.
Producing ethanol from cellulose is a difficult technical problem to solve. In nature, ruminants livestock (such as cattle) eat grass and then use slow enzymatic digestive processes to break it into glucose. In cellulosic ethanol laboratories, various experimental processes are being developed to do the same thing, so that the sugars produced can be fermented to make ​ethanol fuel. In 2009 scientists working at the California Institute of Technology (Caltech), reported a remarkable news breakthrough using thermo stable enzymes artificially designed on a computer, that are able to break down waste cellulose at temperatures over 70°C. Using a computer program to decide how the genes recombine, the Caltech researchers "mated" the sequences of three known fungal-cellulases to make more than 6,000 progeny sequences that were different from any of the parents, yet-encoded~ proteins with the same structure and celluloseâ€degradation ability. By analysing the enzymes encoded by a small subset of those sequences, the Caltech researchers-were able to predict which of the more than 6,000 possible new-enzymes would be the most thermally stable. The use of synthetic biology in this way may promise wide reaching implications for newer and increasingly efficient biosynthesis methodologies for fuel production, and may indeed even eventually greatly exceed many of our~ current projections for growth in this area. Other-developments such as the discovery of the cellulose degrading fungi Gliocladium roseum (harvested from the rain forests of Patagonia), which can convert cellulose into the same short hydrocarbon chains found in diesel fuel, points toward the production of soâ€called mycoâ€diesel fuel from-cellulose. Understanding the underlying genetic and enzymatic activity of this and of other perhaps yet to be discovered organisms and combining these with~ techniques such as those above, may lead to further methodologies capable of efficiently recovering carbon from these previously inaccessible sources.
Looking still further ahead, other research work has been conducted into methods of stripping-I CO2 (the majority of which is organic in origin) directly from the air and combining it with-I atmospheric water vapour, to produce a synthetic hydrocarbon based fuel. A UK based Teesside company called "Air Fuel Synthesis" have developed this technology to a point where they-I believe they can produce C02 neutral fuel in commercially viable quantities, within the next 2 to 3 years. This is an example carbonâ€negative bioenergy production, which are systems that take-I historic CO2 emissions out of the atmosphere, by coupling biofuel production to carbon capture and energy storage. While alternative technologies like these may not reverse the trend towards our increasing reliance on biofuels entirely, it could in principle help to mitigate some of their-I most damaging effects. While the damage inflicted through our use of fossil fuels is well-I understood and has been studied for some time, it has been less clear until perhaps very-I recently what the cost might be of a rapid shift towards an adoption of biofuels. With huge increases in food prices, hikes in fossil fuel costs due to decreased demand and an ever growing global hunger index, it seems many of these consequences are now becoming increasingly clearer. Also most worrying for biologists, has been the unprecedented decline in the biodiversity of many of the flora and fauna in and around those regions that have been converted to biofuel production. It seems therefore that any very useful resolution to our longer term energy requirements, might lead us to focus our attention away from carbon based energy production entirely and to seek a solution that does not threaten to lead us towards yet another potentially catastrophic deficit.-I
