Study On Modified A~2/O Process In Changchun Southern Wastewater Treatment Plant

With rapid increase of state financial input in wastewater treatment sector, wastewater treatment plants with different treatment capacity and process have been built and put into operation.At present, urban wastewater treatment technology in China attaches importance to not only organic removal but also to pollution control of nitrogen and phosphorus on receiving water. Therefore, efficient denitrification and dephosphorization process gradually becomes focus of both study and application. Due to its economic technological advantage and environmental benefit, A~2/O (Anaerobic/Anoxic/Oxic) process is widely used. Wastewater treatment industry in China is at a high-speed development stage. Problems, such as copying treatment process blindly, applying design parameters mechanically and paying attention only to building while overlooking management, emerge in the high-speed development.Study target of the article----Changchun South Wastewater Treatment Plant is one of State Songhua River Basins Pollution Control 11TH Planning Projects, and a key project in Jilin province and Changchun city. Total investment in Phase I is 455 million CNY. Daily design wastewater treatment capacity is 150,000tons. The Plant adopts A/A/O process, effluent reaches to discharge standard of State Class I Type B. Design treatment capacity of treated wastewater reuse is 50,000tons per day, which adopts coagulation, sedimentation and filtering process. The treated effluent will be used as recycle cooling water for Datang No.3 Thermal Power Plant.The article makes a systematic analysis on various forms and process mechanisms of modified A~2/O treatment process. Based on monitored data of wastewater quality in the drainage area of the WWTP, influent quality is determined in 90-95% guarantee rate. Effluent discharge standard is determined as Class I Type B of < Pollutant Discharge Standard of Urban Wastewater Treatment Plant>(GB18918-2002) on basis of ground water function classification of the receiving water—Yongcun River. Considering low wastewater temperature in winter and insufficient carbon sources, traditional design parameters are optimized and adjusted, a detailed process design is developed, with the modified A~2/O process as a core treatment process, and a set of design parameters with reference value are summarized. Construction of Phase I of the WWTP commenced on April 25, 2007, opening and trial operation started on November 28, 2008. The WWTP passed environmental appraisal acceptance and put into operation on August 24, 2009. Wastewater reuse of advanced treatment satisfied the opening requirements in December 2009.The real value of a wastewater treatment plant lies in stable operation after the plant put into operation. Lack of coordination in design, construction and management now becomes an obstacle to progress of China wastewater treatment technology. The author participates in early stage of project design, and makes a tracing study on starting operation, commissioning, trial operation and stable operation, for purpose of providing sufficient experience data and process parameters with reference value to similar wastewater treatment plants.In aspect of starting operation, since lack of experience in modified A~2/O activated sludge cultivation, meanwhile considering low influent load, starting operation mode of continuous influent, continuous aeration and total cultivation is adopted. Starting operation lasted 1 month, cultivation of activated sludge is successfully completed, effluent index gradually reached to or was inferior to design standard. Average value of effluent BOD5 is 10.2mg/l, average removal rate of BOD5 reaches to 82.3%. Average value of effluent COD is 40.6mg/l, average removal rate of COD reaches to 82.3%. Average value of effluent SS is 9mg/l, average removal rate of SS reaches to 86%. Average value of effluent TP is 0.9mg/l, average removal rate of TP is 64.2%. Average value of effluent NH3-N is 5.03mg/l, average removal rate reaches to 89.7%. Indexes of effluent reach to standard of Class I Type B, which indicates that starting operation after sludge cultivation is successful. Indexes of influent and effluent indicate that the system produces a sound impact resistance capability.In aspect of stable operation, a analysis of the whole production data is conducted. Operation data indicates that modified A~2/O process works stably, which has a higher removal rate on BOD5, COD. Average value of effluent COD is 58mg/l, average removal rate reaches to 88.2%; Average value of effluent BOD5 is 14.2mg/l, average removal rate reaches to92%; BOD5, COD of effluent reach to discharge standard of Class I Type B of GB18918-2002, the system has a higher load impact resistance capability.In aspect of N,P removal capability, in period of stable operation, when average value of influent NH3-N is 37mg/l, average value of effluent NH3-N is 5.55mg/l, removal rate of NH3-N reaches to 98.5%, indicating a sound effect for nitrification. When average value of influent TP is 5.25mg/l, average value of effluent TP is 0.9mg/l, removal rate of TP reaches to 73.4%. Indexes of effluent N,P in period of stable operation are superior to or reach to standard of Class I Type B, which indicates that modified A~2/O process has a good effect on denitrification and dephosphorization, and adjustment of process parameters in the WWTP is successful.The article also makes a study on SS removal of the system and influence of surrounding conditions such as temperature on the system. In period of stable operation, when average value of influent SS is 276mg/l, average value of effluent SS is 15mg/l, removal rate of SS reaches to 94%, which reaches to discharge standard of GB18918-2002 Class I Type B(SS is 20mg/l). Influence of system temperature on removal rate of BOD, COD, SS, NH3-N is not great, while system temperature has some influence on removal rate of TP. The lower the system temperature is, the higher the removal rate of TP is, which is consistent with the relevant reports.The article makes a study on design, operation, management and control of modified A~2/O process wastewater treatment plant, summarizes some experiences, which is of reference significance to normal operation of wastewater treatment plant, to realization of economic, social and environmental benefits, and to improvement of urban wastewater treatment plant operation and management.