Study on Influence of Nitrate on Induction of Denitrifying Phosphate Accumulating Organisms

The enrichment of denitrifying phosphate accumulating organisms (DNPAOs) is the prerequisite for the denitrifying phosphate removal process. This study investigated the effect of nitrate concentration on the enrichment of DNPAOs was studied with batch experiments. The Sequencing Batch Reactor (SBR) was set-up with acetate as the sole carbon source. The addition of nitrate solution and the anoxic time were gradually increased with time. Denitrifying phosphorus accumulation was observed soon, but the concentrations of nitrite and nitrate in effluent were fluctuated at the beginning. Then adjusting nitrate concentration according to the ratio of phosphate uptake to nitrate consumption get by batch experiment, the removal efficiency of phosphorus and nitrogen reached 95% and 96%, respectively, and phosphorus concentration in effluent was always lower than 0.5 mg/L in the following days. It was estimated that the percentage of DNPAOs in total PAOs increased from 27.61% (before induction of DNPAOs) to 78.61% (after induction of DNPAOs), by calculating the maximum anoxic or aerobic phosphorus uptake rate under the same conditions. Keywords-DNPAOs; nitrate concentration; induction