POTENTIAL ALTERNATIVES Using agricultural waste rather than actual agriculture to create biofuels removes the need for land conversion—much of the stuff is just lying around—and produces more fuel than corn:
In the case of corn stover (the leaves and stalks remaining in the field after corn is harvested), 250 million dry tons are produced each year and are rarely utilized, other than to feed grazing cattle immediately after a harvest. Scientists believe that some stover should remain in the field to prevent soil erosion, but that still leaves about 40 to 50 percent to be used in making biofuels. An efficient way to break down cellulose into ethanol is necessary to reduce the cost of processing corn stover on a commercial scale. Last February, the Department of Energy selected six companies to receive funding towards building ethanol plants—scheduled to be operational within the next three years—that will utilize new technology for processing corn stover as well as other types of agricultural waste.
In contrast to corn stover, wood waste has limited potential due to the high cost associated with collection and transportation (in the case of wood left over from timber harvesting) and competing uses (in the case of mill residues, which are currently used for mulch, particle board, and to power other facilities).
Many farms have already developed methods of converting the billions of tons of animal waste produced each year into methane for electrical and heat energy; beginning in March, 1,200 households in California will be powered by cow manure. Still, using animal waste to create biofuels is not yet feasible on the national level because transporting it is unrealistic. It's in areas where there are lots of cattle (and the large amounts of manure they inevitably give back to the world) that companies are best equipped to divert animal waste from contaminating the air (via methane, CO2, and ammonia gases) and water towards fueling ethanol production. One example is Panda Ethanol, which is building the largest biomass plant in the United States in Hereford, Texas, where it will use the waste of 3.5 million grazing cattle to fuel the production of approximately 115 million gallons of ethanol per year.
In the United States, 96 billion pounds of food is wasted each year and much of it ends up in landfills where it emits greenhouse gases. Through anaerobic digestion—the bacterial breakdown of organic materials—food waste can be converted into biofuel. In California, Onsite Power Systems, Inc. has begun commercial production of an anaerobic digester system that uses a special design to create the optimal environment for bacteria and ultimately more efficient and cost-effective conversion of food waste to biogases (hydrogen and methane). These biogases can be used in cars or to heat homes.
Algae may be the most promising biofuel. Not only does algae use carbon dioxide to grow (and could potentially use CO2 from power plants to create biofuel), but it can grow anywhere and does not require a large area to propagate. Some species are made of up to 50% of their body weight in oil which can be extracted and processed to create biodiesel. Currently, the National Renewable Energy Laboratory is collaborating with Chevron to develop more cost-effective processes for growing and harvesting large quantities of the green fuel.
