Study On HCR Process Modification Test Of Wasterwater Treatment Plant In Xiao Shan District

Discharge standard of pollutants for municipal wastewater treatment plant (GB 18918-2002) comes into effect from Jul.1, 2003 in China. Comparing with the criterion on wastewater treatment in Integrated wastewater discharge standard (GB8978-1996), the new standard raise the effluent standard on nitrogen and phosphorous. In this case, technical modification will be proposed in many municipal wastewater treatment plants which are constructed before or in an overload situation. China's the fifth five-year plan took the technical modification of wastewater treatment plants as significant part. This study was proposed in that background.Through the analysis on the running data of the Xiaoshan wastewater treatment plant and the investigation on site, the conclusions can be induced. The biological degradation property of the influent is relatively low. Hydraulic retention time (HRT) of the system is too short, so is the sludge retention time (SRT). Aeration is far from the need of pollution removal. The water discharged in a jet break the activated sludge into pieces. And there is no district for the removal of nitrogen and phosphorous. All of these reasons above result in the running problems of the wastewater treatment plant.Single factor analysis is taken in the pilot experiment. These conclusions can be induced. First, the removal rate of nitrogen behaves a direct radio with dissolved oxygen. Since the rate is considerable when the dissolved oxygen concentration is in range of 2.0~2.5mg/L, a up limit of 2.5 mg/L is suggested. Secondly, as an important factor in A2/O process, SRT can not be too high or too low. 20~25d is proposed. Thirdly, when the dissolved oxygen exceeds 1.0 mg/L, the variety of TP in effluent is inapparent. It also indicated that the value of dissolved oxygen concentration need not too high. Fourthly, the removal rate of phosphorous is affected by SRT greatly, shorter of SRT, higher of the removal rate.Considering the special water quality and circumference in Xiaoshan wastewater treatment plant, a suitable operation mode is proposed: SRT=20~25d, return sludge ratio=40~50%. In this operation mode, pollutants in effluent can achieve the standard at a chance of 100% in the pilot experiment.According to the deficiency in pilot experiment, optimization on design parameter is carried out. First, the HRT in anoxic district is reduced to 2.5h from 3.0h. So the primary settling tank can be modified to anoxic district, avoiding the modification on...