The enzymology of sludge solubilisation utilising sulphate reducing systems: Properties of proteases and phosphatases

The first stage in the degradation and recycling of primary sewage sludge (PSS) and particulate organic matter is the solubilisation and enhanced hydrolysis of complex polymeric organic carbon structures associated with the anaerobic sulphidogenic environment. Protease and phosphatase enzyme activities were predominantly associated with the organic particulate matter of the sewage sludge. Sonication of the sludge gave an increase in enzyme activity as the enzymes were released into the supernatant fluid. pH optimisation studies showed a broad range of proteolytic activities with prominent enzyme activity at pH 10, while the phosphatases had greatest activity at pH 4.5. Temperature optimisation studies demonstrated neutral proteases surviving temperatures up to 70 °C, those at pH 5 and 10 with temperature optima at 50 and 60 °C and phosphatases at 60 °C, respectively. All enzymes indicated extensive stability for several hours at their respective optimum temperatures and pH.