Availability of low and high molecular weight substrates to extracellular enzymes in whole and dispersed activated sludges

Our primary objective was to investigate the extent to which the diffusion of high molecular weight compounds through the matrix of exopolymers in activated sludge aggregates reduces their availability to the extracellular enzymes. We found that 17% Of L-Leu-aminopeptidase, 5% of alpha-glucosidase, 23% of protease and 44% of alpha-amylase activities were associated to the easily extractable extracellular polymeric substances (EPS) from the flocs. Surprisingly, when activated sludge flocs were dispersed by the use of both ultrasounds and a cation exchange resin, the rate of protein (azocasein, MW = 25,000) hydrolysis did not increase whereas the rate of polysaccharide (amylose azure, 32,000 < MW < 86,000) hydrolysis increased five-fold. (C) 2002 Elsevier Science Inc. All rights reserved.