Study On Operation Control Of Treatment Process Of A/O-Coagulation Sedimentation For Municipal Wastewater Treatment

This paper takes a city sewage treatment plant in Shijiazhuang city as the research object, the control of the startup operation of the main processing facilities is studied.The technology of the sewage treatment plant is Thick Grid-Small Grid-Aeated Grit-A/O- Coagulating Sedimentation-Filtration-Disinfection, processing capacity of design is 1.6×105 m3·d-1.The total design of sludge age of A/O combined biological pool is11 days.The load of sewage sludge is 0.136 kg BOD5·kg MLSS-1, The sludge production rate is 0.67 kg SS·kg BOD5-1, residence time is 13.7 hours. The facilities of Coagulating Sedimentation are formed by mixed water mixing tank and High density sedimentation tank. The quality of treated wastewater reached the A standard of urban sewage treatment plant pollutant(GB18918-2002).The combined A/O was started up by intermittent water, continuous water influent in after 15 days of aeration. In the process of the cultivation of these two kinds of nitrogen removal microorganisms, the amount of influent was 4 000 m3·h-1, the backflow rate of nitration liquid was 2, the backflow rate of sludge was 50%, the dissolved oxygen level was controlled in the range of 2.0~4.0 mg·L-1, the sludge concentration was between 3 500 mg·L-1and 4 500 mg·L-1. After 30-day operation with continuous procedure, the levels of effluent COD and ammonia were kept were below 60 mg·L-1 and 5 mg·L-1, which can be considered as the nitrogen removal microorganisms have adapted to the sewage environment.The results show that, in order to obtain the effluent COD and ammonia levels below 55 mg·L-1 and 5 mg·L-1, the COD level of the influent should be in the range of 370~430 mg·L-1, ammonia concentration is in the range of 42~48 mg·L-1, the level of dissolved oxygen is in the range of 3~4 mg·L-1, reflux ratio is 2, with increasing the operation loading rates during the start-up period. The operation results indicate that the optimal conditions of operating the combined A/O process include: reflux ratio is 2, the dissolved oxygen level is 4 mg·L-1, and hydraulic retention time is around 14 hours.By making the experiment to the waste water of coagulating sedimentation by PAC and PES. The results show that the PAC is the best coagulant and the optimal dosage level is 0.8 mg·L-1. The results also show that, the COD and SS levels of effluent water were 42.1 mg·L-1 and 0.23 mg·L-1 with the removal rates at 17.1% and 81.4%, while the COD and TP levels of influent were in the rage of 47.7~54.6 mg·L-1 and 1.17~1.38 mg·L-1, respectively.