Study On The Full-scale Trial Of Sewage Plant With CASS Process

The water pollution problem caused by nitrogen and pHospHorus becomes seriously day-by-day along with the development of social economy, the standard of wastewater discharge is controlled more strictly. Therefore, the wastewater techniques developed gradually from the period of pure COD removal to the period of simultaneous COD, nitrogen and pHospHorus removal. The application and investigation development of the new wastewater treatment process with the function of nitrogen and pHospHorus removal has been the study focus.CASS process is a novel wastewater treatment process with the function of nitrogen and pHospHorus removal, which has been applied more and more often these years and has a broad marketing prospect in our country, due to many merits such as little floor space, no need for preliminary and secondary sedimentation tanks, low cost of capital construction and operation, preventing sludge bulking effectively and convenient operation and management.To promote the investigation development of CASS process, especially the application in municipal sewage treatment, from the starting,debugging to the test running of the sewage plant, a series of production tests were carried out. Chongqing dadukou sewage plant as the experimental field, the performance of CASS process was studied roundly, the influence on operation effect of different operation conditions was also studied.After the equipment debugging,clear water ganged debugging, Chongqing dadukou sewage plant began the period of waste water ganged debugging, mainly focused on the culturing and domesticating of activated sludge. The experience has shown that activated sludge culturing and domesticating is completed by twenty days using inoculation method, the removals were 80.4%～90.1%,88.6%～93.7%,83.1%～92.1% for COD,BOD5 and SS respectively, all the indicators of the effluent could meet and even better than the designed target. But the removals of NH₃-N and TN were unideal, the indicators of the effluent could not meet the the standard of discharge. Through the denitriding system debugging, adopting prolong the aeration times and promote the C/N of the influent and so on, the indicators of the effluent could meet the the standard of discharge, the removals are better than the designed target. In the period of test running, the removals were 80.8%,91.8%,87.9%,87.1%,67.7% and 95% for COD,BOD5,SS,NH₃-N,TN and TP respectively.Then the influence of different operation conditions of the CASS were studied. The influence of three different kinds of cycle when the areation time were 2h,3h and 4h on CASS process were compared. Experimental result showed that the effects on carbon and pHospHorus of the three different kinds of cycle differed little, though the sub-effects of chemistry depHospHorization were not exclusive. But at the present of influent, the areation time of 2h was not enough for the NH₃-N and TN removals. The indicators of NH₃-N and TN of effluent could not meet the standard of discharge many times. The rate of NH₃-N of effluent which could not meet the standard of discharge was 42%, and the average of TN of effluent even could not meet the standard of discharge, so the areation time of 2h was not taken. When the areation time was 3h, the removals were 91.2%,89.7%,59.7% and 96.1% for COD,NH₃-N,TN and TP respectively and the removals of 4h were 89.1%,98.2%,63.7%å’Œ96.2% respectively.In the premise of the effluent could meet the standard of discharge no matter the areation time were 3h or 4h, taking the areation time of 3h will save the cost of running. Experimental were carried out to seek the optimum DO controls parameters. The result indicated that when the DO concentration was controlled between 2.5～3.0 mg/L, CASS process performed best. Taking the energy-saving into consideration, the best DO concentration was 2.5mg/L. The removal efficiencies of COD,NH₃-N,TN and TP were respectively 88.9%,94.5%,71.3% and 95.8%, the COD,NH₃-N,TN and TP concentration of effluent were 33.0,2.2,17.1 and 0.18mg/L.The performances of CASS in winter (December) and spring (March) were compared (Study on the influence of temperature, summer should be taken into consideration, but the plant adjusted the influent in June and the influent was as same as the designed, the operation conditions also modified. So the datas were not comparable to the winter and spring). The influence of temperature on nitration was strong. With the boost of temperature, NH₃-N removal efficiency assumed an upward trend, the removal efficiency of TN and NH₃-N maintained synchronism. Because the aeration time was relatively abundant to pHospHourus taken-up, the temperature was not the limitation factor, so the TP removal efficiencies of different seasons were close, the effluent were also very low, ranged from 0.1 to 0.5 mg/L.The performances of CASS process under the differentλwere studied. The less theλwas, the stronger the capability of resisting shock load CASS had and the higher the removal efficiencies of different pollutants were. To the influent quality and the performance of CASS now, no matter taking whichλ, the effluent always can meet the standard of discharge, so it also showed that the CASS process had a strong capability of resisting shock load.