| The increasingly heavy water pollution makes municipal wastewater treatment necessary. After about 5 months acclimation, the effluent quality also can not meet designed standard, so the in-situ pilot test was carried out by CASS reactor in TaiZhou 1st Municipal Wastewater Treatment Plant in order to obtain excellent effluent and lower energy consumption. Moreover, the large-scale experiment would be adjusted by pilot test results, so the all pollutants'removal and introduced problems during the large-scale operation would be investigated and discussed in the paper.The in-situ pilot experiment for municipal wastewater treatment, which has lasted for 5 months, was carried out in order to investigate operation parameters, such as operation period and the time of feed, aeration, settling and decant, drainage ratio, temperature and return ratio and so on. And the results showed that the excellent effluent quality and relatively lower energy consumption would be obtained with the operation period of 6h including feed 1h, aeration 1.5h, settling 2.5h and decant 1h, which was acted as optimal operation period; The effluent quality was detected with drainage ratio of 1/4, 1/3 and 1/2.5, and the mean COD removal of 89.1%, 86.1% and 76.0%, the mean NH3-N removal of 90.6%, 90.1% and 89.7%, the mean TN removal of 56.2%,51.2% and 47.1% and the mean SS removal of 94.4%, 93.3% and 91.3% were obtained. Which demonstrate that the drainage ratio was lower the higher removal was; Meanwhile, the distinct effect of temperature on CASS effluent quality was found, and only effluent COD could meet designed standard and other parameters, such as NH3-N, TN and SS, were greatly increased and could not meet standard under the condition of lower temperature (5~8℃). Meanwhile, the sludge settling capacity also was poor in lower temperature, and compared with constant temperature, SV and SVI value were increased from 41.7% and 110.2mL/g to 65.5% and 172.1mL/g respectively; The study on CASS with and without return sludge was carried out and it was found that the effluent quality was higher with return than that without return, moreover, the larger return ratio would produce higher effluent quality. It was about 2 months that the large-scale CASS was run based on the pilot results with mean effluent COD, NH3-N, TN and SS lower than 55.0mg/L, 6.87mg/L, 17.1mg/L and 16.4mg/L respectively, which could meet the designed standard. Also, a great deal of lively Vorticella sp. was detected by microscope and the Metazoan-Brachinus sp. also was found usually.However, many problems also took place during the large-scale CASS operation, such as the sludge bulking occurred in one CASS, and it was analyzed that the relatively lower sludge loading resulted in sludge bulking. Therefore, which was controlled effectively by increasing return ratio to 50%, adding the decant ration to 1/2, decreasing DO concentration in oxidation zone, enhancing air flow in anoxic zone and controlling sludge drainage and so on; In addition, the sludge floating also took place because of the longer settling time, so settling and decant time were optimized based on mathematic model, which would shorten the two from 3.5h to 2h, moreover, it not only decreased the settling time, but also prolonged the decant time from 1h to 1.3h, thus decreased the decant loading for decanter. |
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