Acclimation And Influence Factors Study Of Denitrifying Phosphorous Removal Bacteria With Nitrate As Main Nitrogen Source

Enhanced biological phosphorus removal (EBPR) is widely recognized as a cost-effective approach for phosphorus removal from wastewater. As an interesting field of EBPR, denitrifying phosphorus removal process has received much more attention in recent years. This process is operated under alternating anaerobic and anoxic conditions. During the anoxic period, the denitrifying phosphorus-accumulating organisms (DPAO) could utilize nitrate or nitrite as electron acceptors to uptake phosphorus, which is released in the anaerobic period. The phosphorus is removed by discharging the residual sludge containing high concentrated phosphorus. Compared with the conventional phosphorus removal process, denitrifying phosphorus removal process offers significant advantages. Recently, many researches have been conducted to study the cultivation of DPAO and the effects of some factors on DPAO. However, to our best knowledge, most existing researches reported that only ammonium was used as nitrogen source and the effects existed great difference under varied cultivation modes. The present study explored the cultivation of DPAO using nitrate as main nitrogen source for the first time. Moreover, influence of nitrite and ammonium on the phosphorus removal performance of DPAO were also investigated.Firstly, activated sludge was used as the seed sludge and then cultivated in a sequencing batch reactor (SBR) with nitrate as the main nitrogen source for DPAO cultivation under alternating anaerobic, anoxic and aerobic conditions. Assays of phosphate, nitrate, nitrite and etc. were conducted during the 330 days cultivation period. The changes of various indicators within one cycle, together with dynamic kinetics analysis were also investigated during each cultivation period. Fluorescence in situ hybridization (FISH) and 16S rRNA gene sequence analysis were carried out to investigate the composition of bacteria. The results showed that with the acclimation of DPAO, both the phosphorus-release rate and quantity increased gradually in the anaerobic period, and phosphorus removal efficiency reached 91.8% with a complete consumption of nitrate. The dynamic analysis indicated that the anaerobic phosphate-release and anoxic/aerobic phosphate-uptake fitted the first order kinetics equation. Phosphorus-accumulating organisms (PAO) accounted for 80.56% of the total bacteria and the DPAO occupied more than half of the PAO. Comparing with the PAO, the glycogen-accumulating organisms (GAO) was only 5.6% of the total bacteria counts. Moreover, although the fluctuation of phosphorus in effluent were observed when the influent and environmental factors changed, the nitrate concentration in effluent remained stable. Therefore, it was indicated that cultivation of DPAO with nitrate as main nitrogen source was feasible, which offered significant removal efficiency of both phosphorus and nitrate. Under this condition, PAO became the dominate strains. Furthermore, continuous experiments showed that the simultaneous nitrogen and phosphorus removal performance of the SBR was kept stable under the optimal conditions.In addition, the effects of nitrite and ammonium on the cultivated DPAO were investigated. Batch experimental results showed that nitrite could serve as electron acceptors in anoxic period for denitrifying phosphorus removal with an addition concentration of 75 mg/L. Meanwhile nitrite inhibition could be observed as the nitrite concentration over 100 mg/L. The influent nitrite could cause significant inhibitory effect on DPAO in anaerobic period. When the DPAO was exposed to ammonium, the increase in ammonium dosages resulted in both anaerobic-release and anoxic-uptake of phosphorus increase. Then, the inhibitory effects of nitrite and ammonium on DPAO and the recovery of DPAO activity were also studied through SBR. During short-term operation, when the nitrite concentration was 40 mg/L, the system could recover after the inhibition. However, irreversible suppression was observed while the concentration of nitrite increased to 80 mg/L, phosphorus removal rate was only as 70% as before. When the ammonium concentration was 80 mg/L, although the levels of released and uptaked phosphorus were increased, the total phosphorus removal efficiency was not affected obviously with a constant ammonium removal performance.