Study On Treatment Of Piggery Wastewater By Earthworm Biofilter

The pollution problem caused by the development of the livestock farms is drawing more and more concerns. Now, combined with the other technics, anaerobic biological treatment is the main method of aquaculture wastewater treatment. But it exist some shortcomings ,such as, large area of coating line occupation, greater prophase investment and high energy consumption.With the advantage of energy conservation, ecology, environment-friendliness, being- manageable, vermifilter is a potential wastewater treatment process to treat aquaculture wastewater.The contents of this study include: technological design of piggery sewage used by vermifilter, study of vermifilter’s stationary phase, optimum structure, factors that affect the vermifilter, mutual interaction among earth-worm ,plant, microorganism and its influence on treatment efficiencies of pig manure.1. After the treatment of Vermifilter which achieves stability , the TOC influent concentration from 79.34 mg/ml drops to 35.40 mg/ml, and the removal efficiency of vermifilter observed is 55%.so it is feasible to use the Vermifilter to treat the piggery sewage.2. With the different structure of vermifilter,the time of stability for the removal efficiency of COD_Cr,BOD₅,NH₄⁺-N and TP are of difference.The time of COD_Cr,BOD₅,NH₄⁺-N and TP are in the range of 30～50 d,45～50 d,40～45 d,35～50 d,and the process of stability can be matched with the curve S equation: y = A2 + （A1-A2）/（1 + exp（（x-x0）/dx）） Because of the different structure, parameters of the S curve equation and the time of stability need vary.3. Under the applications of uniform design method,the best of the structure of vermifilter is obtained :the ratio of the dealing with the middle layer is 3:1, the proportion of sawdust in the processing layer is 83.33%, the proportion of chaff in the middle layer is 1, and the density of the earthworm is 3003 item/m².In which , the removal efficiency of COD_Cr,BOD₅,NH₄⁺-N and TP are 61.4%, 47.6%, 45.7% and 40.7%.4. The overall function of vermibiofilter is increased slightly by the introduction of plants, mainly embodied in two aspects: Firstly,enhancing the capacity of resistance to impact load,from 0.02 m³Â·m^-2·d^-1 increased by 0.01 m³Â·m^-2·d^-1; secondly, increasing the capacity of purification, by the introduction of water celery, the removal of the COD_Cr,BOD₅,NH₄⁺-N and TP increased by 7%, 8.7%, 10.5% and 12%.5.The average removal efficiency of COD_Cr,BOD₅,NH₄⁺-N and TP were 65.71%,54.12%,51.41%,41.99%;57.28%,50.69%,51.41%,41.99%;and41.11%,34.79%,30.73%,31.84% respectively under the condition of summer,autumn,and winter. Temperature has greater influence on the vermifilter,which was largely embodied in the activity and survival of earthworm, thereby affecting the ability to treat wastewater.6. The removal of COD_Cr,BOD₅,NH₄⁺-N and TP of piggery sewage are closely related to the effects of vermifilter and metabolism of various organisms. An appropriate survivial environment is provided by earthworm activity, plant growth for the microorganism in the vermifilter, promoting the distribution of microbial populations and stocks and Conducive to the degradation of pollutants. The results show that the dominant functional microorganisms in the vermifilter are mainly bacterias and actinomycetes.7.The piggery sewage treated by vermifilter can be used for farmland irrigation,pigpen washing, or combined application with the technology of constructed wetland . and the discharged wastewater met the national standard. With the advantage of less engineer cost, less investment,less operation cost,simple management and higher resource degree,it is appropriate for the current wastewater treatment of small-scale pig farms in China.