HYDROLASES IN THE ORGANIC-MATTER FRACTIONS OF SEWAGE-SLUDGE - CHANGES WITH COMPOSTING

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 exhibited highest activity in the 210-day compost and the lowest molecular weight fraction (< 10(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-alpha-benzoyl-L-argininamide and phosphatase and between these and carbon content, in both the extracts of organic matter and derived fractions.