Treatment Of Rural Domestic Sewage Using Modified Vertical-Flow Multi-Soil-Layering System

Domestic sewage in rural areas of China is often discharged into natural water bodies without effective treatment,which has a serious impact on residents' health,ecological environment and agricultural production.Considering the financial condition and population distribution of rural areas,an efficient,cost-effective and environmentally friendly decentralized sewage treatment technology will become an important strategy for the solution of the problem.A modified multi-soil-layering(MSL)system was developed to treat the low C/N ratio sewage in rural areas.The results showed that MSL had good performance in sewage treatment under complex conditions.The highest removal rates of COD,TP,NH4+-N,NO3--N and TN during the operation could reached 98.29%,100%,76.60%,96.15%and 69.86%,respectively.In order to improve the performance of system,the study selected a 23-factor design based on factorial design to study the effects of the operating parameters on the system.The three operating parameters selected were the factor A-the mass of artificial carbon source(butylene succinate-PBS),the factor B-the mass of activated sludge and factor C-the bottom submerged height of devices.The results show that the effects of single factor are significant and there are interactions between different factors.In order to simulate and predict the nitrogen removal of MSL system,a nitrogen removal model which could predict the removal rate of TN was developed.A clustering tree which could predict removal rates of TN was obtained,and the minimum error was less than 0.01%.In order to study the changes of components within the system,the 16S rRNA microbial diversity test was carried out on the soil mixture blocks of device to study the species composition and community diversity when the operation was accomplished.The results showed that in terms of species abundance,the experimental samples,the soil samples and the activated sludge samples were in descending order.As for the community diversity,the soil samples,experimental samples and activated sludge samples were in descending order.The effects of three factors on the Beta diversity of the experimental samples were factor B,factor A and factor C from large to small.The soil test results showed that total nitrogen,total phosphorus and organic matter were greatly improved after operation.At the same time,plant cultivation proved the feasibility of using experimental soil for reuse in farmland.Therefore,the modified MSL system will be of great significance for the treatment of decentralized wastewater in rural areas.