| With the economic development and the transformation of production and life style,the water quality in China's rural areas is continually deteriorating.It is showed in a survey that rural sewage is one of the main sources of water pollution,and a potential threat to water resources security,restricting the sustainable development of the rural society and economy.Thus,a sustainable rural sewage treatment technology with high efficiency,low consumption has become one of the important research directions in the field of water pollution control.According to the rural water pollution characteristics and the current situation of the rural areas,and also in the aim of energy conservation,emissions reduction and resource utilization,a new process of rural sewage treatment was developed combined with large depth-diameter ratio anaerobic reactors,anoxic deodorization reactor,dripping aeration reactors and combined artificial wetland,which is called biological and ecological wastewater treatment system.The combined system is as efficient as anaerobic-anoxic-aerobic biological treatment technology to remove pollutions,and also as easy to manage and maintain as artificial-wetland ecological process.In this dissertation,the pollution removal efficiency of the combined system was studied in the following aspects.(1)The process optimization and operation characteristics analysis on large depth-diameter ratio anaerobic reactors;(2)The process optimization of denitrification deodorization of anoxic reactors;(3)The pollution removal efficiency and biological membrane characteristics analysis in dripping aeration reactors;(4)The research on nitrogen and phosphorus resource utilization and pollution removal mechanism and the operation optimization of the aquatic-vegetable-type artificial wetland and the subsurface constructed wetland;(5)based on the research above,a combined system process model is established and verified in practical treatment.The main research results are showed briefly as below:1.The effects of hydraulic retention time(HRT)on organic removal rate,gas production and outlet odor threshold number were investigatedof the large depth-diameter ratio anaerobic reactor in different water temperatures.The results show that as the increase of HRT in different water temperatures,the gas production and the outlet odor threshold number will be reduced;When the water temperature is bellow 12?,it is necessary to prolong the HRT to guarantee the organic removal effect.Considering carbon source utilization,the organic matter in sewage should be anaerobically digested into biogas in order to achieve organic matter degradation and biomass utilization at the same time.2.The anoxic deodorization reactor is suspended inside with elastic filler inside,where the anaerobic effluent and the aerobic reflux converge,carrying out anoxic denitrification.The effects of reflux ratio and HRT on the performance of the anoxic deodorization was studied in different water temperatures.The TN,H2S,Volatile Fatty Acid(VFA)and the odor threshold were significantly decreased with the increase of reflux ratio.The water temperature has a significant effect on the reaction efficiency,and in low water temperature,the reflux ratio can be increased to ensure the removal rate of main odor matters exceeding 60%.3.The staged dripping aeration device is optimized to acquire best aeration performance and nitrifying efficiency.The results show that,with the improved device,the removal rate of organic matter and ammonia can reach more than 50%.Under the condition of the test water quality,a satisfactory performance would be obtained when the COD volume load were less than 1.5 kgCOD/(m3·d).4.The process characteristics of the aquatic vegetable wetland and subsurface flow constructed wetland were investigated.The optimum hydraulic loading of aquatic vegetable wetland is 0.2 m3/(m2·d),and the optimum water depth is 10cm.Harvesting 1/4 of the vegetables every time can achieve effective nutrient removal and higher vegetable production.The absorption effect of spinach in wetland and microbial degradation are the main ways for TN removal,and the removal contribution was 51.14%and 47.87%respectively;TP was mainly removed by the absorption of water spinach,and the removal contribution was 61.92%.It is proposed to use the mode of pre aquatic vegetable wetland and post subsurface flow constructed wetland,in order to ensure the stability of the effluent.The food safety analysis of the vegetables(water spinach and celery)in the wetland system,shows that the pesticide residues and heavy metals in vegetables does not exceed the national standards,which encourages its practical popularization.5.Based on the conservation of materials,the pollutant removal model for each reactor and the coupling model of the whole process of the biological and ecological wastewater treatment system for rural domestic sewage were established.The deviation between the simulated results of the process model and the measured values were less than 25%.Each reactor model and the whole process coupling model can be used to predict the running effect of the combined system and adjust operating conditions.The results of this study indicate that biological and ecological wastewater treatment system combined with large depth-diameter ratio anaerobic reactor,anoxic reactor,dripping aeration reactor and artificial wetland can effectively treat rural sewage,and realize the resource utilization of organic matter,nitrogen and phosphorus in the sewage.The results have significant value for the construction of sustainable rural sewage treatment system with high efficiency and low energy consumption,and the improvement of rural water environment quality. |
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