OCCURRENCE OF DENITRIFYING PHOSPHORUS REMOVING BACTERIA IN MODIFIED UCT-TYPE WASTE-WATER 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 th e 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 s howed a clear difference of denitrifying dephosphatation activity betw een 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 fol lowing possible reasons for the lower proportion of (denitrifying) dep hosphatation activity in the WWTP-Genemuiden sludge in comparison with the WWTP-Holten sludge, were suggested; (a) nitrate/oxygen transfer t o the anaerobic/anoxic zone due to the internal recirculation inside t he treatment plant, (b) lower amounts of fatty acids in the influent d ue to shorter retention time of waste water in sewer lines, and (c) lo wer amount of nitrate recycled to the anoxic zone. (C) 1997 Elsevier S cience Ltd.