Characterization of the combined effects of enzyme, pH and temperature treatments for removal of pathogens from sewage sludge

The combined effects of enzyme, pH and temperature treatments for removal of pathogens from sewage sludge were investigated. An adjustment to pH 10 for 24-h at 23 degreesC or a 3-h hold at 50 degreesC resulted in a 100% kill of coliforms but a significant count of Salmonella species still survived. However, pH adjustment to 12 with a hold of 48-h at 23 degreesC or pH adjustment to 10 or 12 and a 3-h hold at 60 degreesC was required to achieve a 100% kill of Salmonella species. Although protease enzyme treatment at 40 degreesC with or without alkali treatment eliminated coliforms completely, Salmonella counts were reduced by two to three orders of magnitude. However, complete elimination of pathogens was observed when enzymatic treatment was provided at 50 degreesC. Application of alkaline protease, through its combined beneficial effects in pathogen reduction, solids reduction and improved solids settling, has potential as an effective procedure for processing of sewage sludge.