| Because of the existed problem that insufficient carbon source in wastewater and high aeration energy consumption for biological nitrogen and phosphorus removal in domestic wastewater, a novel process based on SBR was proposed with seven stages:feeding-anaerobic stage-low oxygen aeration stage-anoxic stage-aerobic stage-sedimentation-drainage. Phosphorus release conducted in anaerobic stage, simultaneous nitrification and denitrification (SND) in low oxygen aeration stage, denitrifying dephosphatation in anoxic stage, nitrification and phosphorus uptaken in aerobic stage, the combination of SND and denitrifying phosphorus removal was achieved in the single sludge system.SND sludge and denitrifying phosphorus sludge were mixed after the sludge acclimation finished. The combination of SND and denitrifying dephosphatation was achieved. With the normal temperature, MLSS of 3800mg/L-4000 mg/L, SRT of 20d, pH of 7.8 and water filling ratio of 66%, the stage duration periods for anaerobic stage, SND stage, denitrifying dephosphatation stage and aerobic stage were 2h,3h,3.5h and 1h, respectively, when the sodium acetate was the single influent carbon source, COD was 150mg/L and COD/TN/P was 25:5:1 in the artificial wastewater, the TN and TP removal rate were 66.7% and 96.1%. The percent of TN removed through SND and denitrifying dephosphatation were 39.8% and 17.1%, respectively. The percent of TP removed through low oxygen phosphorus uptake and denitrifying dephosphatation were 68.4% and 22.7%, respectively. The effluent concentrations of COD, NH4+-N, NO3-N, NO2-N, TN and TP were <10mg/L,2.16mg/L,11.28mg/L,0.03mg/L,13.47mg/L and 0.83mg/L, respectively.The amount of phosphorus release in anaerobic stage and phosphorus uptake in low oxygen stage in combined-SBR increased with the increase of initial pH. The cause of initial pH affect anaerobic phosphorus release process was because of different anaerobic glycogen metabolism and activity of ADK and PPK under different initial pH. Cell synthesis ability increased with the increase of initial pH, and higher initial pH has higher nitrification and denitrification activity. ADK and PPK activity increased with the increase of pH as well. A higher sodium acetate and sodium propionate/sodium acetate ratio can cause higher TP removal efficiency, but the ratio has little impacts on TN removal rate. The enzyme activity of DH, PPK and ADK increased with the increase ratio of sodium propionate/sodium acetate. When sodium propionate was used as the sole carbon source for 20d, the effluent concentrations of COD, TN, TP and NH4+-N were<10mg/L,11.39mg/L, 0.51 mg/L and 0.02mg/L, respectively.To achieve effective carbon source utilization and efficient nutrient removal in the combination of SND and denitrifying phosphorus removal system for low ratio of COD/N in wastewater, the distribution of substrate should be controlled by adjusting the phase period time. The external carbon source should be removed in anaerobic and low oxygen stage, and sufficient internal carbon source was synthesized for low oxygen and anoxic stage. The relative abundance of PAO, AOB, NOB, and denitrifier existed in the combined-SBR after stable operation was 41±11%,10±4%, 13±9%and 16±12%, respectively. The substrate type in influent and initial pH has influence on the competition of GAOs and PAOs, higher initial pH benefits PAOs compete for GAOs. With the increased percentage of sodium propionate in influent, the relative amount of PAOs increase accordingly, while the relative number of AOB, NOB and dentrifier has no correlation with substrate type.The combined-SBR system enhanced the efficiency of nitrogen and phosphorus removal by applying SND and denitrifying phosphorus removal technology, it can enrich and maintain nutrient removal related microorganisms. The process, which relieved the carbon source competition between denitrification and anaerobic phosphorus release and reduced the oxygen demand, is suitable for the treatment of domestic wastewater with low C/N. |
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