Biological Phosphorus Removal Process Improved And Upgraded On An A~2/O Process Sewage Treatment Plant In Xi’an

With the rapid development of Xi ’an in recent years, more and more domesticsewage and industrial wastewater is discharged into the Weihe River, which leads to aserious water pollution in the water basin. The deterioration of water environmentintensifies the task of water pollutants emission reduction.According to the nationalTwelfth Five-Year Planning and Three-year action plan about Weihe River Basin WaterPollution Control (2012-2014), it is imperative to upgrade the urban sewage treatmentplant emissions standards from the level B to level A (on the basis of the Urban SewageTreatment Plant Pollutant Discharge Standards), in order to reduce the emissions andimprove the water environment.Based on the above background, a monitoring of water pollutants along the wholeA2/O process was implemented, and it was found that the main factor which restrictingthe effluent to achieve level A standard is the relatively poor biological phosphorusremoval effect. Research results show that the main factors which affecting phosphorusremoval efficiency includes three aspects:(1) Reflux sludge which has highconcentration of phosphorus increased the load of phosphorus removal process;(2) Thereturn sludge from the second pond introduced nitrates into anaerobic tank inhibition ofphosphorus release process;(3) The main group of carbon source in the inflow water isparticle state COD, which is difficult been used by microorganisms. Besides, during thephosphorus release process the utilization rate of carbon source is low, which leads toeven poorer phosphorus removal efficiency. For the matter concerning the high phosphorus concentration of reflux sludge water,the method of individual treatment of the sludge water was adopted to reduce the impactof reflux sludge water on the phosphorus removal process. For the inhibit effect ofnitrate on phosphorus removal, filler medium was added to increase the efficiency ofdenitrification, phosphorus removal and simultaneously to improve the utilization rateof carbon source. Regarding to the shortage of carbon source, the number of primarysettling tank and residence time was reduced, so as to decrease the loss of carbon source.With the measures mentioned above, the effluent water quality was improved afterrehabilitate: On the one hand, the impact of the reflux water was reduce; on the otherhand, the loss of carbon source was decreased, which means the utilization rate ofcarbon sources was increased; moreover, the phosphorus removal efficiency wasincreased by17%compared with before. After the reconstruction project，the totalphosphorus in the effluent was0.45mg/L on average，which has reached the level A ofthe Urban Sewage Treatment Plant Pollutant Discharge Standards.