Analysis Of Rural Sewage Microbial Community Structure And Its Recycling Utilization Risk

The rural sewage is particularly huge and difficult to concentrate it in China. It is appropriate to treated dispersedly, but the treatment efficiency is very low. Free flowing wastewater seriously affects the environmental sanitation of the village, led to dirty, disorderly and poor rural environment, and it is also the source of the infectious disease. It is an important mission to remove the pollutants in the rural sewage and make it recycling utilized for building new socialist countryside. In order to evaluate the feasibility of rural sewage irrigation, terminal restriction fragment length polymorphism (T-RFLP) and 16S rDNA clone library technology were employed in this research to analyze the microbial community structure in wastewater of membrane bioreactor (MBR) system. Effects of wastewater irrigation on quality indices of plants and physicochemical properties of soil were studied through pot experiment. Dynamic changes of pathogens in MBR and phyllospheric pathogens residue of Chinese cabbage were observed by using fluorescence quantitative PCR technology. The main conclusions were as follows:(1) The MBR system had high microbial diversity, and maintained stability relatively in a certain extent, where the Shannon index was kept in the range of 1.82-3.56. This indicated that the treatment system has a certain buffering capacity. Proteobacteria accounted for a considerable proportion (91.8%) in rural sewage, among which Arcobacter sp. was the dominant bacterium of rural wastewater (68.5%). Quantitative analysis showed that 10 kinds of pathogens were detected in different phases of the MBR system and reduced 0-4 orders of magnitude after membrane reactor without disinfection, the removal up to 95% for the most pathogens, and the treatment effect was obvious.(2) After sewage irrigation, the plant yield and its soluble sugar content obviously increased, the soluble protein content didn’t significantly affect, nitrate content in the plant increased significantly, and the nitrate in plants accumulated as the irrigation time prolonged. The effect of long-term irrigation on plant nitrate content needs to be further monitored, although it is still within the scope of safety standards. Reclaimed water irrigation had no significant effect on plant. Short-term wastewater irrigation didn’t affected soil pH obviously while it increased the soil conductivity, organic matter content, activity of urease and phosphatase. Long-term wastewater irrigation can make the soil pH decrease while the soil conductivity, organic matter content, activity of urease and phosphatase continuously increase. Effects of reclaimed water irrigation were consistent with wastewater irrigation, but the influences were relatively small.(3) Rural sewage direct irrigation increased the residue of the pathogen on phyllosphere of plants and led to health risks, while irrigated with reclaimed water from the MBR system didn’t increased the residue of the pathogen. In order to ensure food safety and reduce the infection of intestinal pathogens, sewage should irrigate in the root of vegetables rather than spray irrigation, reduce direct contact with vegetables and stop irrigate before vegetables come into market. Fresh vegetables should be washed for many times and heated before eating.