ENZYMATIC-ACTIVITY IN THE ACTIVATED-SLUDGE FLOC MATRIX

The enzymatic activity of activated sludge was investigated with speci al emphasis on the localization of the enzymes in the sludge flee matr ix. Activated sludge from an advanced activated-sludge treatment plant , performing biological N and P removal, was used. An enzymatic finger print was established using a panel of six different enzymes. The fing erprint revealed peptidase as the most dominating specific enzyme test ed. By monitoring sludge bulk enzymatic activity over a 3-month period using fluorescein diacetate as an enzyme substrate, considerable vari ations in activity were observed even over short periods (a few days). The variation in esterase activity was to some extent correlated to t he presence of humic compounds in the sludge, but not to the sludge pr otein content. Comparison of full sludge enzyme activity to the activi ty of a batch-grown sludge culture indicated that enzymes accumulated in sludge flocs. A large proportion of the exoenzymes were immobilized in the sludge by adsorption in the extracellular polymeric substances (EPS) matrix. This was demonstrated by extraction of EPS from the act ivated sludge using cation exchange. Contemporary to the release of EP S a very large fraction of the exoenzymes was released into the water. This showed that the exoenzymes should be considered to be an integra ted part of the EPS matrix rather than as direct indicators of the mic robial activity or biomass.