Hydrolases in the organic matter fractions of sewage sludge: Changes with composting

Abstract Four extracellular hydrolases (urease, phosphatase and two proteases) and organic carbon content were determined in organic matter extracted from a non-composted sewage sludge and one composted for 91 and 210 days (the latter having undergone a maturation step). These parameters were also determined in organic fractions of different nominal molecular weight, obtained by controlled ultrafiltration. Organic matter extracted from the non-composted sewage sludge had a higher enzyme activity than that from the composted sewage sludge. The organic fraction with the highest enzyme activity was that of intermediate molecular weight (ranging from 10 3 to 10 4 ) except for urease which lowest molecular weight fraction ( 3 ). Composting influenced urease and phosphatase activity in the sludge. In non-composted mixtures hydrolases showed relative high activity values and, with minor exceptions, equal distribution in fractions with molecular weight > 10 3 , while in the composted materials urease and phosphatase activity was greatest in the organic fraction of size 10 3 –10 4 molecular weight. High positive correlations were obtained between proteolytic activity on N-α- benzoyl- l -arggininamide and phosphatase and between these and carbon content, in both the extracts of organic matter and derived fractions.