Laboratory and pilot plant studies are described for a new Esso-Carver Greenfield process for the disposal of sewage sludge. An oil-assisted gravity separation of the majority of the water while heating is followed by multiple effect evaporation to dryness in an oil slurry, and incineration of the dry solids. Agreement between laboratory and pilot plant results was good, indicating no scale-up problems. In the gravity separation, secondary sludges are concentrated from about 0.5% up to 5-10% solids. Solids capture of 98% or more is achieved by high shear oil-sludge contacting. Temperature dependent losses of solubilized organic carbon up to about 25% of the organic content of the feed are observed in the separated water from the oil concentration, and in the distillate from the evaporators. The process economics show an advantage of $13-32 a ton compared to the best known commercial technology: total costs are estimated at $21-39/ton of dry solids for a 189 ton/day plant processing a 50/50 mixture of primary + activated sludges to ash. A lower temperature gravity separation step could greatly reduce the economic penalty for a 25% recycle of solubilized secondary sludge.

"EPA-670/2-74-004." "February 1974." Report prepared by Esso Research & Engineering Company, Linden, New Jersey.