Presidential Green Chemistry Challenge: 1996 Academic Award
Professor Mark Holtzapple of Texas A&M University
Conversion of Waste Biomass to Animal Feed, Chemicals, and Fuels
Innovation and Benefits: Professor Holtzapple developed a family of technologies that convert waste biomass, such as sewage sludge and agricultural wastes, into animal feed products, industrial chemicals, or fuels, depending on the technology used. Because these technologies convert waste biomass into useful products, other types of basic resources, such as petroleum, can be conserved. Also, the technologies can reduce the amount of biomass waste going to landfills or incinerators.
Summary of Technology: A family of technologies has been developed by Professor Mark Holzapple at Texas A&M University that converts waste biomass into animal feed, industrial chemicals, and fuels. Waste biomass includes such resources as municipal solid waste, sewage sludge, manure, and agricultural residues. Waste biomass is treated with lime to improve digestibility. Lime-treated agricultural residues (e.g., straw, stover, and bagasse) may be used as ruminant animal feeds. Alternatively, the lime-treated biomass can be fed into 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 are hydrogenated to their corresponding alcohols such as isopropanol, isobutanol, and isopentanol.
The technologies above offer 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 exacerbates soil erosion and requires intensive inputs of fertilizers, herbicides, and pesticides, all of which contaminate ground water.
Chemicals (e.g., organic acids and ketones) may be produced economically from waste biomass. Typically, waste biomass is landfilled or incinerated, which incurs a disposal cost and contributes to land or air pollution. Through the production of 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.