| Due to the long-term urban-rural dual structure, the sewage treatment in Shanghai urban and rural areas is significantly different with a much lower sewage treatment rate in rural areas. As one of the major sources of pollution of the water environment in rural areas, indiscriminate discharge of sewage has a serious impact on the overall compliance rate of water environment quality and water function area in Shanghai suburb areas. Therefore, in recent years, Shanghai water departments put increasing emphasis on distributed sewage remediation and management in suburban and rural areas.This study set the rural sewage treatment projects which were belong to the Shanghai Waterworks Special Project as the research object. After summarizing the characteristics of rural sewage treatment projects, the data of long-term follow-up monitoring of outlet water quality in the typical decentralized rural sewage treatment system were analyzed and the applicability of the technique and economic applicability of the different processes were evaluated. Based on Threshold Theory, and the combination of process mechanism and the actual situation in suburbs, the research of the classification guidance of rural sewage treatment system in Shanghai was carried out.Research and conclusions can be summarized as follows:(1) After sorting out the situation of Shanghai rural sewage treatment projects, the progress of Shanghai rural sewage treatment project, the technique application status and application-orientation were analyzed. The conclusions of the analysis were:①At the end of2011, the sewage collection and treatment of95,500farmers in Shanghai had been completed and the amount of construction in the districts and counties were quite different.②On-the-spot treatment was the main rural sewage treatment in Shanghai and the surrounding rural areas in some suburbs (3.77%) towns used the municipal treatment.③There were a variety of on-the-spot sewage treatments used the rural areas in Shanghai. At present, the on-the-spot sewage treatments were mainly distributed treatments and the percolation treatment process was the most widely used. However,in recent years, some biological treatment processes like the biofilter gained a wider application.④Shanghai rural sewage treatment process has some problem in selected extensive guide, lack of technology demonstration and scale distributed processing.(2) The technology applicability assessment of Shanghai typical rural sewage treatment process was based on the tracking and monitoring samples which included the effectiveness and compliance of the process, the conclusions of the analysis were:①Different ways of anti-seepage in soil infiltration treatment processes caused a significant difference in water quality. The reason for the poor anti-seepage effect was the damage in the process of construction and operation which could easily lead to the penetration of the groundwater treatment system;②The result of the evaluation of the process effectiveness and process compliance demonstrated that mature sewage treatment process should be core areas biotypes+eco-combination process, for example, in the case of contact oxidation+artificial wetlands,the abnormal process monitoring data rate was low and the technical applicability was relatively best. However, the ecotype process such as constructed wetlands+soil percolation process, the process compliance rate was poor, the proportion of abnormal data were67.7%and11.0%, respectively, which didn’t meet standards of the areas with a requirement of high water quality.(3) Comparative analysis of the differences of the different processes from land costs, infrastructure costs and operation and maintenance costs, and urban sewage treatment plant design criteria and the actual operation and maintenance costs compared to assess the economic applicability of Shanghai rural sewage treatment typical process, The conclusions are as follows:①Compare the costs and expenses of the Shanghai decentralized rural sewage treatment systems and urban sewage treatment plant from land costs, infrastructure costs and operation and maintenance costs, results show that the distributed process much higher than the real economic costs of municipal wastewater treatment plant.②Economic applicability of biological sewage treatment process (including combination process) is relatively good, the construction cost and operating costs maintaining costs of dealing with large-scale contact oxidation+artificial wetlands and biofilter+artificial wetlands were at a low level, and the land cost remained in the moderate range.③However, the construction cost of small-scale ecological treatment process, such as soil infiltration, reached33,000Yuan/(m3/d), the maintaining cost was4.07Yuan/m3, and the land cost is20m2/(m3/d).(4) Based on the threshold theory, management decision-making recommendations for the guidance on the classification of the Shanghai rural sewage treatment were made.The conclusions of the decision were:①The rural sewage treatment process in water source protection area should select water quality standards as the "threshold".Mature sewage treatment process with the combination of core areas biotypes and eco-combination process was recommended for the process with a larger processing scale while good nitrogen biological phosphorus removal treatment process such as (Integration A2/O) could be applied to the process with a smaller scale.②To treat a larger area in non-water source protection zones, the selection of process should satisfy the requirements of appropriate economic cost, especially small single process with low land cost including gravity oxygen artificial ecosystem bed, and composite Biofilter Process. Moreover, the combination of technology can deal with high-strength hydraulic shock caused by large-scale processing.③In view of the lack of effectiveness of the process and the high land cost of soil infiltration, the sphere of application of this process was limited to non-water source protection areas with the treatment scale no more than10m3/d. |
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