Occurrence of denitrifying phosphorus removing bacteria in modified UCT-type wastewater treatment plants

The occurrence of denitrifying phosphorus removing bacteria (DPB) and the contribution of DPB to phosphorus removal in full-scale wastewater treatment plants (WWTPs) has been investigated by batch tests with the activated sludge from two WWTPs (WWTP-Genemuiden and -Holten). Both WWTPs are operated as UCT-type processes. Batch tests to evaluate the biomass composition of the sludges were developed. These batch tests showed a clear difference of denitrifying dephosphatation activity between the WWTP-Genemuiden and -Holten sludge. In the sludge of the WWTP-Genemuiden the (denitrifying) dephosphatation activity was rather low, whereas a high activity was formed in the WWTP-Holten sludge. The following possible reasons for the lower proportion of (denitrifying) dephosphatation activity in the WWTP-Genemuiden sludge in comparison with the WWTP-Holten sludge, were suggested; (a) nitrate/oxygen transfer to the anaerobic/anoxic zone due to the internal recirculation inside the treatment plant, (b) lower amounts of fatty acids in the influent due to shorter retention time of waste water in sewer lines, and (c) lower amount of nitrate recycled to the anoxic zone.