BIOLOGICAL DEPHOSPHATATION BY ACTIVATED-SLUDGE UNDER DENITRIFYING CONDITIONS - PH INFLUENCE AND OCCURRENCE OF DENITRIFYING DEPHOSPHATATION IN A FULL-SCALE WASTE-WATER TREATMENT-PLANT

The effect of pH on phosphorus release under anaerobic conditions was examined for denitrifying phosphorus removing bacteria (DPB) cultivate d in an anaerobic-anoxic sequencing batch reactor, Also batch tests we re conducted with activated sludge from a full-scale waste water treat ment plant (WWTP) in order to investigate occurrence and contribution of DPB in phosphorus removal processes. In the experiments for the pH effect, enriched DPB sludge was maintained under anaerobic conditions with acetic acid (HAc) present at 5 different pH conditions (6.0 simil ar to 8.0), and released phosphorus and consumed HAc concentrations we re measured. When the biomass concentration was around 2.7 g-VSS/l, th e observed P/C (released-P / consumed-HAc) ratios were 0.7, 1.1 and 1. 2 g-P/g-C at pH = 6, 7 and 8, At 4.2 g-VSS/l, the observed P/C ratios were 0.9, 1.3 and 1.2 g-P/ g-C, respectively, The difference between t he two experiments resulted from the endogenous phosphorus release. Th e same pH effect as observed for conventional anaerobic-aerobic SBR sl udge, was obtained for the DPB sludge in the range of pH = 6.0 similar to 7.5. However due to precipitates formation at pH = 8.0, the appare nt P/ C ratio was approximately 20% less than the ratio calculated fro m the biological released phosphorus concentration by DPB, From the re sults of the batch tests with activated sludge and observations on the full-scale WWTP, it was also shown that clearly denitrifying dephosph atation occurs and approximately 50% of the phosphorus removal occurs via denitrifying activities in the WWTP. (C) 1997 IAWQ. Published by E lsevier Science Ltd.