Assessment of biological activity during temperature changes in a bench-scale sequencing batch reactor fed with synthetic medium containing lignin

The influence of temperature on activated sludge in a bench-scale SBR fed with a synthetic medium simulating paper mill effluents was determined using biological methods based on the measurement of enzymatic activities. Redox activity inside cells and in the extracellular polymeric substances as well as the proportion of active cells in the sludge were measured by the reduction of the tetrazolium salts XTT and CTC, respectively. A significant shift in the size distribution of lignin at 30°C correlated with a maximum of extracellular redox activity. The percentage of active cells in the biocoenosis was independent of temperature, α-glucosidase and L-alanine-aminopeptidase activities were steady at 20, 30 and 40°C. After shifting the temperature to 50°C there was an enormous short-time increase of both enzyme activities because of the change from mesophilic to thermophilic conditions. Of the biological parameters tested, only extracellular redox activity correlated with degradative activity as detected by a change in molecular size distribution of lignin molecules.