Alternatively, the lime-treated biomass can be fed to a large anaerobic fermentor in which rumen microorganisms convert the biomass into volatile fatty acid (VFA) salts such as calcium acetate, propionate, and butyrate. The VFA salts are concentrated and may be converted into chemicals or fuels via three routes. In one route, the VFA salts are acidified releasing acetic, propionic, and butyric acids. In a second route, the VFA salts are thermally converted to ketones such as acetone, methyl ethyl ketone, and diethyl ketone. In a third route, the ketones may be hydrogenated to their corresponding alcohols such as isopropanol, isobutanol, and isopentanol.
This family of technologies offers many benefits for human health and the environment. Lime-treated animal feed can replace feed corn, which is approximately 88 percent of corn production. Growing corn requires plowing, which exacerbates soil erosion; approximately two bushels of top soil are lost for each bushel of corn harvested. Also, corn requires intensive inputs of fertilizers, herbicides, and pesticides, all of which are contaminating ground water.
Chemicals (e.g. organic acids and ketones) may be produced economically from waste biomass that has a negative impact on the environment, such as municipal solid waste and sewage sludge. Typically, these wastes are landfilled or incinerated, which incurs a disposal cost while contributing to land or air pollution. By producing chemicals from biomass, nonrenewable resources such as petroleum and natural gas, are conserved for later generations. Because 50 percent of U.S. petroleum consumption is now imported, displacing foreign oil will help reduce the U.S. trade deficit.
Fuels (e.g. alcohols) produced from waste biomass have the benefits cited above, i.e., reduced environmental impact from waste disposal and reduced trade deficit. In addition, oxygenated fuels derived from biomass are cleaner burning and do not add net carbon dioxide to the environment, thereby reducing factors that contribute to global warming.