Robert A. Graff

Biography

B.Ch.E., 1955, New York University M.S., 1957, D.Eng.Sc., 1963 Columbia University

Research Interest

Environmental regulations have forced New York City to cease its long standing practice of disposing of municipal sewage sludge by ocean dumping. Land disposal is now required, and this waste is now transported as far as Texas, Arizona, or Colorado, at high cost. A process is under development to reduce these costs. Sludge under pressure is heated rapidly by steam injection to about 220?C and quenched after 10 to 30 seconds. The resulting solubilization of organic matter substantially increases methane yield in subsequent anaerobic digestion. This reduces the amount of sludge requiring land disposal. Equally important, in terms of cost savings, is the improvement in sludge dewaterability resulting from the process. New York City now prepares its sludge for transport by centrifugation. To meet specifications, polymer coagulant must be added. After processing, however, characteristics of the sludge are improved to the point that coagulant is not needed, eliminating this costly and polluting material. Cost estimates for the introduction of the process into existing plants show a substantial advantage in comparison to present plant operation.