Anaerobic bacteria -- microbes that live without oxygen -- are helping to turn plant and animal waste into energy and to clean up waste discharges.Skip to next paragraph
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Although the concept of burning biogas released from waste products has been around for centuries, waste producers in the United States have only recently begun to use the technique.
Currently, there are about a dozen major anaerobic digesters producing biogas on a commercial basis. This gas is about 60 percent methane and 40 percent carbon dioxide. It can be compressed for storage or used immediately to produce energy on site.
In most cases, operators finance their systems by selling electricity back to their local power companies, as well as by their own energy costs. Energy use on site often involves ''cogeneration,'' in which waste heat produced by the biogas process is also used as an energy source.
Ancient civilizations used naturally occurring biogas for cooking. Today, most such gas is produced outside the US. In China, for instance, there are an estimated 7 million family-size digesters, plus 560 rural power stations fueled by animal and plant waste. While some municipal waste water systems generate methane in the US, the inclusion of highly toxic industrial wastes usually confines that production to the later stages of effluent treatment.
Meanwhile, the private commercial digesters already ''on stream'' are working examples of how the entire waste product can be used. Besides producing energy and nutritious food supplements, the systems eliminate most environmental pollutants, greatly reduce odor, and speed the conversion of waste-treatment settlement lagoons into a reusable water supply.
Mr. Umstadter has worked to help set up four systems in the US and Guatemala for dairy and livestock waste. He says he considers that the lush tropical areas of Latin America have great potential for producing energy from fruit and vegetable waste.
Turning a manure processing system into a plant digester requires little alteration. It is more a matter of ''materials handling,'' he explains. Recently Agway, a leading agricultural cooperative in the Northeast, agreed to market the AES systems through their outlets.
Mr. Umstadter had been active as project manager in helping nearby Kaplan Industries install what now is the country's largest methane digester at its cattle feedlot and 250,000-head-a-year slaughterhouse. The project, funded largely with a $920,000 grant from what is now the Department of Energy, was completed in 1979. The digester can process 25 tons of manure a day. This generates $158,000 worth of methane and $380,000 worth of nutrient-rich byproducts annually.
Before it had the methane digester and anaerobic-aerobic lagoon system, Kaplan had been discharging one-quarter- to one-half-million gallons of waste water daily from its processing plant and feedlot. Kaplan officials had installed an earlier lagoon system themselves. They modeled it after similar settlement lagoons used throughout Europe.
Seven empty phosphate pits, left behind by strip-miners, provided a pond system with the help of separating dikes. The first several anaerobic ponds in the 100-acre system held nutrient-rich solids, which settled out there. Succeeding ponds were oxygen-supporting (aerobic) bodies of water. The first, deeper ponds promoted a natural anaerobic conversion of the methane - which was then lost in the atmosphere - while the subsequent, shallower ponds promoted the cleansing, aerobic action to make the water reusable on-site.