Pretreatment technology for the beneficial biological reuse of municipal sewage sludges

Modern municipal sewage waste treatment plants use conventional mechanical and biological processes to reclaim waste waters. This process has the overall effect of converting a water pollution problem into a solid waste disposal problem (sludges). The costs for conventional disposal of Sewage sludges have risen dramatically because of increased environmental mandates, which restrict their disposal, as well as a dwindling number of landfills. Previously, we determined that secondary bioprocessing (specifically anaerobic digestion) was not effective in reducing the organic content and bulk of the sludge waste (1). Therefore, we have examined the potential of a variety of pretreatment technologies designed to disrupt the macrostructure of the sludge and thereby enhance its subsequent biodegradation. Two thermal/mechanical pretreatments tested were found to have a dramatic effect on the subsequent bioconversion of the microbial sludges. Both technologies evaluated, sonication and shear, were found to be affected by sludge solids levels, duration of treatment, and treatment temperature. Optimum sonication pretreatment occurred with sludge solids of 1% and treatment times of 4-8 min. The most effectivee treatment temperature tested was 55 degrees C. The optimum enhancement in bioconversion potential for the sonication pretreatment was 80-83% of the materials carbon oxygen demand (COD) content. The optimum shear pretreatment occurred with sludge solids of 1-2% and treatment times of 6-10 min. The most effective treatment temperature tested was 87 degrees C. The optimum enhancement in bioconversion potential for the shear pretreatment was 88-90% of the material's COD content. These data were the basis for US parent no. 5,380,445, granted January 10, 1995.