Historical Perspective: Farm (Manure) Digesters

THE history of BioCycle’s coverage of anaerobic digestion can be traced back to its inaugural issue in Spring 1960, when the journal, originally named Compost Science, published “Composting Manure by Anaerobic Methods.” Dr. Clarence G. Golueke of the Sanitary Engineering Research Laboratory at the University of California, Berkeley — and a member of the founding Editorial Board — wrote the article, concluding that “reduction to a stable humus by anaerobic digestion seems to offer great promise for a relatively inexpensive and yet completely sanitary method of disposing of manure.”

Golueke described a simple process of “dumping or flushing all wastes into an airtight container in which bacteria can break down the organic matter to form humus and a combustible gas. The procedure provides sanitary treatment of organic wastes and results in a great reduction in flies. It also makes possible the efficient and economical recovery of some of the waste carbon as methane for fuel. It produces humus and nutrients for use on soils. Moreover, both liquid and solid wastes may be treated in one operation. Practicality of the process has been demonstrated by its successful use on European farms.”

Golueke noted that the “evolved gas is approximately two-thirds methane and one-third carbon dioxide,” which is pretty standard in the literature. He continued: “Thirty-five cubic feet of the gas compares to one quart of alcohol, 52.5 cubic feet of manufactured city gas, or 2.2 kilowatt hours (kWh) of electrical energy. The humus remaining after digestion is comparable to that obtained from digesting sewage sludge. It has a nitrogen content varying from one to two percent by dry weight.... Digester size and number will depend on the quantity of wastes available. For example, 1,400 pounds of cow manure without bedding and with normal moisture will require approximately one cubic yard of digester space. Space requirements for an equivalent manure naturally will increase according to the amount of bedding used.”

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