Study On Treatment For Small Town Sewerage With The Combination Process Of Biological Filter And Biological Contact Oxidation Tank

Since the reform and opening up, urbanization is speeding up in China, but most of the small towns in our country failed to establish the sewage collecting and treating facilities, wastewater was discharged without treatment to the nearest natural water directly, which was a huge threat to the water environment. Given the characteristics of sewage water and the pecuniary condition in small towns, the small towns cannot use the wastewater treatment process of medium or big cities’. Therefore, to establish decentralized sewage treatment facilities can realize the rapid disposal of sewage in small towns, this research developed a kind of sewage treatment technologies for the small towns in China, namely “the combination process of biological filter and biological contact oxidation tank”.The main contents in this research were as follows:1) There were two kinds of start-up modes, inoculate start-up and natural strat-up. The natural strat-up mode of the biological filter needed 20 days to achieve stable removal effects, which COD and NH4+-N removal rates were about 55% and 40%; the inoculate mode of the biological contact oxidation tank needed 20 days to achieve stable removal effects, which COD and NH4+-N removal rates were about 85% and 80%. Both biofilm reactors were microscopy, observed a large number of bio-indicators, such as zoogloea, filamentous fungi and a few paramecium, nematodes and amoebae, these were the signs of success of the reactors start-up.2) The study of hydraulic loading, gas-water ratio and temperature on the pollutants removal efficiency.We got the optimized operating condition of the combination process on the basis of univariate analysis,which was the hydraulic loading of 0.125m3/m2·h,temperature of 20~25℃, gas-water ratio of 12:1. Under the optimized conditions,the average removal rates of COD, NH4+-N, TN, TP and SS were 89.3%, 84.5%, 70.4%, 71.1% and 82.8%,the quality of effluent was stable and can reach the discharge standards.3) The research on resistance of load capacity of the combination process. In the event of influent water strike, water hydraulic loading from Q0(Q0 as designed hydraulic loading, Q0=0.125 m3/(m2·h)) increased to 1.5Q0,2.0Q0 respectively, the water quality index of the effluent increased, but after 12 h, the effluent COD, NH4+-N and TN can reach level I B discharge standards.4) The research on microbiological characteristic. The microorganisms in the anoxic zone of the anoxic biological contact oxidation tank were mainly as dark gray sheet like zoogloea, the biofilm in the aerobic zone of the anoxic biological contact oxidation tank was thick with the color of brown. The biomass of per unit area of packing was within the range of 0.3~0.6 mg in the biological contact oxidation tank, the biomass of per unit area of packing was about 0.3 mg in the biofilter, and the microorganisms in the biological contact oxidation tank were more microbial activated than the microorganisms in the biofilter. Through the determination of specific oxygen uptake rate(SOUR), it can be seen that the biological activity and oxygen consumption rate of the lower part of the biofilter and biological contact oxidation tank were higher than the upper ones.