The effect of added carbon source and nitrate concentration on the denitrifying phosphorus removal by denitrifying phosphorus removal bacteria sludge was systematically studied using batch experiments, at the same time the variation of ORP was investigated. Results showed that the denitrifying and phosphorus uptake rate in the anoxic phase increased with the high initial anaerobic carbon source addition. However, once the initial COD concentration reached a certain level, which was in excess of the PHB saturation of Poly-p bacteria, residual COD carried over to the anoxic phase inhibited the subsequent denitrifying phosphorus uptake. This was equal to supplementing the external carbon source to the anoxic phase, furthermore the higher the external carbon source concentration the more powerful the inhibition caused. High nitrate concentration in the anoxic phase increased the initial denitrifying phosphorus rate. Oncethe nitrate was exhausted, phosphate uptake changed to phosphate release. Moreover, the time of this turning point occurred later with the higher nitrate addition. On the other hand, through on-line monitoring the variation of the ORP with different initial COD concentration, it was found that ORP could be used as a control parameter for phosphorus release, but it is impossible to utilize ORP for controlling the dinitrification and anoxic phosphorus uptake operations.

No abstract

The Anaerobic-Anoxic/Nitrification (A2N) system is a continuous-flow, two-sludge process in which Poly-P bacteria are capable of taking up phosphate under anoxic conditions using nitrate as an electron acceptor. The process is very efficient because it maximizes the utilization of organic substrate for phosphorus and nitrogen removal. An experimental lab-scale A2N system fed with domestic sewage was tested over a period of 260 days. The purpose of the experiment was to examine phosphorus removal capacity of a modified A2N two-sludge system. Factors affecting phosphorus and nitrogen removal by the A2N system were investigated. These factors were the influent COD/TN ratio, Sludge Retention Time (SRT), Bypass Sludge Flow rate (BSF) and Return Sludge Flow rate (RSF). Results indicated that optimum conditions for phosphorus and nitrogen removal were the influent COD/TN ratio around 6.49, the SRT of 14 days, and the BSF and RSF were fixed at about 26-33% of influent flow rate.