Study On Biological Character And Turbidity Removal Mechanism Of Biological Sand Filter In Treating Micro-polluted Water

Taking the Fuyang river as source waterthe problems of biological sand filter's biological character and mechanism of removal turbidity in micro-polluted water were studied in this paper. It was studied biological sand filter removing organic matters, NH₄⁺-N, NO₂^--N, turbidity, Fe and Mn through pilot-plant experiments. Furthermore, several factors considered affecting biological sand filter had been examined. Analytic Hierarchy Model was used to analysing affecting factors. Further, the thickness of biofilm was confirmed by microscope and calculated. The paper was studied on biomass and microbial activity in biological sand filter. It was investigated the influence of biomass and bioactivity under different temperature, start-up methods and backwash, Analyzed the oxygenize performance.The results show biological sand filter can remove various pollutants effectively. The removal rates of COD_Mn, TOC, UV₂₅₄, DOC and SCOD are 34.55%, 33.65%, 22.85%, 40.02% and 50.13%, respectively; The removal rates of NH4+-N and NO2--N can reach 74.47% to 91.86% and 68.24% to 92.26%; The removal rates of Fe and Mn can reach 65.51% to 86.47% and 69.88% to 84.18%; The removal rates of colourity can reach 44.44% to 66.67%. It was measurement separately with natural operating situation at normal temperature. The factors such as temperature, substrate concentration and filtering velocity are analyzed in this paper. It applied Analytic Hierarchy Model for analyzing affecting factors, the results show that temperature, substrate concentration and filter velocity were the important factors. Their weights are respectively 0.301, 0.251, 0.115.After the biological sand filter stabilization operated, the biomass and bioactivity of biological sand filter are 31.03nmolP/g and 0.123 mgO₂ /h·g, the thickness of biofilm was 50～84μm, The influence of temperature for biomass is smaller, but the bioactivity is bigger. The change of biomass and microbial activity in biological sand filter by backwashing. The results show that the max reduced rate of biomass in biological sand filter is 22%, the bioactivity is enhanced.Oxygenation performance of biological sand filter is investigated, the index of mass transfer and aeration coefficient has good correlation; When aeration are 0.10m³/h and 0.20m³/h, after packing filter material the index of mass transfer enhanced 23.93% and 19.39%, but they gradually approach with the increment of aeration.The results show that the removal rates of turbidity can reach 56.05% to 82.38%, the mechanism of removal turbidity can be considered the common effectiveness of mechanical deposition, biological flocculation and bio-oxidation. Then, it has good correlation that effluent turbidity with inflow turbidity, COD_Mn, UV₂₅₄.