Sludge management by thermal conversion to fuels

Abstract

The philosophy of sludge management in the sewage treatment industry must respond to changes in processing costs and environmental requirements. As overall costs increase, the efficiency of sludge management must be increased either by ugrading the existing scheme or introducing new technology. Both of these approaches are discussed briefly in the paper and it is pointed out that low-temperature conversion of sludge to fuel appears to have considerable potential as a viable new technology.Experimental work carried out at Environment Canada's Wastewater Technology Centre used batch and continuous reactors to evaluate this technology at bench scale. Tests on a number of mixed raw sludges (primary + waste activated) resulted in the following yields: oil, 22–25%, char, 50–60%, noncondensable gas, 10–12%, and reaction water, 5–12%.The impact of a number of sludge treatment alternatives, including the conversion of sludge to oil, are discussed with respect to energy efficiency, flexibility, and public acceptance. The future plans of Environment Canada for the development and demonstration of sludge-to-oil technology are also discussed. Key words: sewage sludge, thermal conversion, energy recovery, sludge management, oil, fuel, char.