| Songhua river played an important role in watershed management, nevertheless the tributary of songhua river–feiketu river is one of main pollution sources. With the development of the economy, the amount of enterprises in industrial area would be more and more, sotbu pollutants discharged seriously exceeded feiketu river capacity. According to special low temperature conditions in northen area, this paper researched on wastewater treatment technology,analyzed the mechanism of simultaneous nitrogen and phosphorus removal and determined the properties of microorganism groups in order to maintain the security of water quality.A~2/O process was developed and the continuous model experiment operated with industrial wastewater was carried out. Firstly the effect of sludge return ratio,mixed liquid recycle ratio,MLSS,SRT and DO on the nitrogen and phosphorus removal was investigated. The sludge return ratio of 50%,the mixed liquid recycle ratio of 300%,MLSS around 2.5~4g/L,the SRT of 15 days and DO around 3~4mg/L were determined as optimal for the normal A~2/O system that reached simultaneous nitrogen and phosphorus removal very well and the concentions of effluent COD,TN,TP were 25.18 ~30.21 mg/L,10.09~12.59 mg/L,0.15~0.28 mg/L respectively. However, the removal of nitrogen in low system was so bad, which the concentions of effluent COD,TN,TP were 27.21~32.19mg/L,16.91~20.89 mg/L,0.20~0.31 mg/L respectively.The microbial activity and metabolic activity especially nitrobacteria decreased at low temoerature conditions. Adding filler as biological reinforcement measure can increase the amounts of biomass and fix nitrobacteria.The results demonstrate that the combined A~2/O process can efficiently improve the removal, which the removal of TN was increased by 20%. Based on the experiments, adding sludge return to aerobic tank was order to enhance nitrification and further decrease the effluent of TN. The result that this way can realize nitrogen and phosphorus removal very well and the effluent meet the standard.Sludge was stained to observe PHAs and poly-P to recognition mechanism of biological phosphorous removal intuitivly. Making use of the electron microscope and scanning electronic microscope, the characters of microorganism and sludge at the normal and the low system were compared. The results indicated that the bacteria phase of the suspended sludge and biofilm was plentiful include various nutrient levels. It is that the processes were operated high efficiently and steady. By scanning electronic microscope, sludge was density at normal temperature, on the contrary, at low temperature was loose and sheet. So the properties of sludge adsorption and settling was bad in low temperature. In addition, sludge bulking was monitored when system was in low loadings or temperature decreased shrarply. It is effective to control slugdge bulking that raise flow of aeration and ensure stable operation.In low temperature, the experient reached good removal of simultaneous nitrogen and phosphorus. It has break through A~2/O process to realize simultaneous removal and temperature effect, which can guide wastewater plant in industrial zone.At the same time, the experimental data were showen to well desigen,operate and regulate wastewater plants in northen region. The combined process and adding sludge return also provided a new way to research nitrogen and phosphorus at low temperature and reconstruct wastewater plants.
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