Estimation of bacterial biomass in urban wastewater by measuring potential exoproteolytic activity
Recent studies have shown that when wastewaters are discharged into a river, heterotrophic bacterial biomass in the effluent exerts considerable influence on the biodegradation kinetics of organic matter and provokes the oxygen deficits often observed downstream from outfalls. Quantification of bacterial biomass in wastewaters is required for a good understanding the biodegradation kinetics. Bacterial biomass can be estimated by epifluorescence microscopy after staining cells with fluorochrome. Applying this technique to wastewater samples, however, is painstaking and difficult. In this study, an alternative method for estimating bacterial biomass in wastewaters was tested; it consists of measuring the potential exoproteolytic activity (PEA) of bacteria. Previous studies on other types of aquatic systems have shown that bacterial biomass can be estimated from PEA. After optimising the PEA procedure for use with wastewater, we found a significant correlation between PEA and the bacterial biomass estimated by epifluorescence microscopy. This opens the way for PEA measurements for rapid and easy estimates of bacterial biomass in wastewaters. As an example of the application of this technique, the impact of wastewater treatment on bacterial biomass in effluent was investigated at various treatment plants. On the basis of our procedure, specific loads of bacterial biomass (load per inhabitant and per day) were calculated for raw and treated wastewaters.