Caption title. At head of title: Project summary. Distributed to depository libraries in microfiche. "June 1986." "EPA/600-S2-86-034."

"Direct, continuous thermochemical liquefaction of primary, undigested municipal sewage sludge was carried out to produce a heavy oil and char product suitable for use as a boiler fuel. The work was carried out in a prototype sludge-to-oil reactor system (STORS) capable of processing sludge with 20% solids at a rate of 30 L/hr. Up to 73% of the energy content of the feedstock was recovered as combustible products (oil and char). The oil product had a heating value of 80% to 90% that of diesel fuel. These products are capable of supplying the energy requirements for dewatering and liquefaction, so that a wastewater treatment plant based on the liquefaction concept can, in principle, be energy-self-sufficient. A standard BOD determination indicated that the wastewater from the process was biodegradable. The only other significant byproduct was a gas composed of more than 95% carbon dioxide. The process is therefore relatively nonpolluting. STORS was operated for more than 100 hr without any sign of corrosion or char buildup on the inside walls. Complete feedstock conversion was achieved at 300ÀC, with a nominal 1.5-hr residence time or 5.8 kg/hr of solids throughput. An economic assessment prepared for a conceptual commercial liquefaction reactor indicated a sludge disposal cost of $43/dry tonne for a city of 1 million. This figure is highly competitive with incineration costs. Projected capital construction costs for a STORS unit were $6.1 million, which is much lower than that for an incineration plant. The process therefore has considerable promise for many potential sites in the United States."