Particular internal recirculation frequency scope for enhancing denitrifying phosphorus removal in an oxidation ditch.

This study investigated the influence of the unique internal recirculation characteristics of an oxidation ditch (OD) system, namely, the internal recirculation frequency (IRF) on denitrifying phosphorus removal (DNPR). The ratios of denitrifying polyphosphate-accumulating organisms (DPAOs) to polyphosphate-accumulating organisms (PAOs) under different IRF conditions were measured using a batch experiment. On this basis, the variation of nutrient transformations was studied using the IRF changes by the mass balance method. The results showed that, for the OD system that had an anaerobic zone upstream from the circular corridor and set anoxic and aerobic zones along the circular corridor, when the IRF was between 3.4 h-1 and 7.5 h-1, the DPAOs/PAOs ratio reached about 50%. Approximately 20% of the total phosphorus (TP) was removed and over 11% of the total nitrogen (TN) was transformed into nitrogen gas by the DNPR process, and meanwhile the total removal efficiencies of the TP and TN were over 93% and 80%. When the IRF was greater than 11.5 h-1, the TN removal efficiency decreased significantly, and this was not conducive to simultaneous nitrogen and phosphorus removal. The results indicated that the OD process would possess a better DNPR potential if the IRF were controlled within the proper scope.

[Effects of Long-term Poly-P Deficiency on the Metabolic Properties of Accumulibacter in AO-SBR System].

To investigate the changes in microbial community structure and metabolic properties of Accumulibacter under long-term Poly-P deficiency, an activated sludge enriched with Accumulibacter was inoculated into two SBR reactors, where sodium acetate and sodium propionate were used separately as organic carbon sources. The two reactors were operated for 60 days with an influent PO43--P concentration of 2.5 mg·L-1. The phosphorus removal performance, sludge production, and changes in the microbial community structure of the systems were analyzed. The results indicated that both SBR systems showed good performance of phosphorus and organic matter removal. However, microorganisms in both systems showed glycogen-accumulating metabolism properties under long-term Poly-P deficiency. In the unfavorable environment of long-term Poly-P deficiency, Accumulibacter Ⅰ maintained a high abundance (40%±7%) in the propionate SBR system, indicating that Accumulibacter Ⅰ had higher metabolic activity and its metabolic properties could be independent of Poly-P for survival under Poly-P deficiency for a long period. In comparison, propionate is more conducive to Accumulibacter adaptation to lower phosphorus loads, and Accumulibacter Ⅰ is more competitive than Accumulibacter Ⅱ under lower phosphorus loads.