POPULATION-DENSITY AND ENZYME-ACTIVITIES OF HETEROTROPHIC BACTERIA IN SEWER BIOFILMS AND ACTIVATED-SLUDGE

The heterotrophic activity of different wastewater biocenoses is assessed. The biofilms originate from a sewer discharging domestic wastewater and from a sewer discharging trade wastewater with chromium and nickel contamination. The activated sludge was taken from the aeration tank from the high load stage (F:M ratio 0.8 kg kg(-1) d(-1)) and from the low load stage (F:M ratio 0.1 kg kg(-1) d(-1)) of a two-stage municipal wastewater treatment plant. We determined the population density of heterotrophic saprophytes, polymer degrading bacteria, ammonifying bacteria as well as of nitrate reducers and denitrifiers. Enzyme activities were determined as relative substrate turnover rates for esterase, alpha- and beta-glucosidase, for phosphatase and for L-alanine-aminopeptidase. The population density of heterotrophic saprophytes was one order of magnitude higher in the high load stage compared to the low load activated sludge. The sewer biofilms showed one to two orders of magnitude higher counts per g dry weight for the heterotrophic bacteria as compared to the activated sludges. The turnover rates of esterase and L-alanine-aminopeptidase were higher than those of alpha- and beta-glucosidase and phosphatase. The sewer biofilms are highly active biocenoses both with respect to population densities as with respect to enzyme activities. Their heterotrophic activity is comparable with the one in high load activated sludge. Even the bacteria in the biocenosis which is exposed to high concentrations of chromium and nickel showed a high activity.