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

The heterotrophic activity of different wastewater biocenoses is asses sed. The biofilms originate from a sewer discharging domestic wastewat er and from a sewer discharging trade wastewater with chromium and nic kel contamination. The activated sludge was taken from the aeration ta nk from the high load stage (F:M ratio 0.8 kg kg(-1) d(-1)) and from t he low load stage (F:M ratio 0.1 kg kg(-1) d(-1)) of a two-stage munic ipal 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 activ ities were determined as relative substrate turnover rates for esteras e, alpha- and beta-glucosidase, for phosphatase and for L-alanine-amin opeptidase. The population density of heterotrophic saprophytes was on e 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 bacter ia as compared to the activated sludges. The turnover rates of esteras e and L-alanine-aminopeptidase were higher than those of alpha- and be ta-glucosidase and phosphatase. The sewer biofilms are highly active b iocenoses both with respect to population densities as with respect to enzyme activities. Their heterotrophic activity is comparable with th e one in high load activated sludge. Even the bacteria in the biocenos is which is exposed to high concentrations of chromium and nickel show ed a high activity.