Research Of Full-Scale UAB-DSB Combined Biofilters For The Treatment Of Domestic Sewage

Due to the high concentration of nitrogen and phosphorus in rural domestic sewage and the low concentration of carbon sources,it is difficult to meet the requirements of conventional activated sludge for the proportion of carbon,nitrogen,and phosphorus in influent water.Moreover,the pollution sources of rural domestic sewage are scattered,and the construction of pipe networks is complex.Therefore,it is of great practical significance to develop new types of decentralized sewage treatment technology.This research is to construct a full-scale combined biofilter device in a rural domestic sewage plant,consisting of up-flow aerated biofilter（UAB）and denitrification shallow biofilter（DSB）,to explore its nitrogen and phosphorus removal efficiency for actual rural domestic sewage.This research firstly carried out a study on the start-up of the biofilters;secondly,explored the impact of process operating parameters on treatment efficiency;thirdly,focused on analyzing the degradation law of pollutants along the route,and established the pollutant degradation kinetic equation;finally,analyzed the microbial community structure of the filter and derive the pollutant removal mechanism.The main research results are as follows:（1）UAB-DSB adopted the inoculation and film coating method to successively start UAB and DSB.Based on the effluent quality as the main judgment basis,combined with the microbial phase and surface characterization of filter media,it is comprehensively determined that UAB started after 39 days,and DSB started after 13days.After successful start-up,the COD removal efficiency was 80.82%,the NH₄⁺-N removal efficiency was 74.61%,and the TN removal efficiency was 77.39%.（2）The gas/water ratio,C/N ratio,and hydraulic load were selected as the main operating parameters to investigate their impact on the nitrogen removal efficiency of the UAB-DSB.The results showed that the optimal gas/water ratio was 4,with a COD removal efficiency of 76.84%,a NH₄⁺-N removal efficiency of 84.81%,and a TN removal efficiency of 77.96%;the optimal C/N ratio was 3-5（DSB）,with a COD removal rate of 32.96%,a NO₃^–-N removal efficiency of 94.47%,and a TN removal efficiency of 58.01%;the optimal hydraulic load is 0.65 m³/（m²·h）,with a COD removal efficiency of 83.06%,a NH₄⁺-N removal efficiency of 76.77%,and a TN removal efficiency of 71.86%.（3）Research on process optimization from micro flocculation enhanced process for phosphorus removal and gas water backwashing.The results show that adding 15mg/L of PAC can enhance the phosphorus removal effect of the process,making the TP in the effluent meet the Class A discharge standard.After 6 hours of air water backwashing,UAB-DSB recovered its treatment efficiency.（4）Based on the concentration of pollutants along the biofilter,the degradation kinetics equations for COD,NH₄⁺-N,and NO₃^–-N were established.The fitting result of that COD degradation kinetic equation was C=C₀e^{0.2341q1.6648h},NH₄⁺-N degradation kinetic equation was K_nln（N₀/N）+N-N₀=4.9503h（hydraulic load was0.65m³/（m²·h））,NO₃^–-N degradation kinetic equation was N=N₀e^0.9825h0^-.¹6.₅⁵（hydraulic load was 0.65 m³/（m²·h））and it could explain the degradation of pollutants along biofilters.（5）The structure and functional diversity of microbial communities along biofilters were analyzed by high-throughput sequencing.The results showed that COD degradation mainly occurred at the bottom of the UAB filter media layer（0.0～1.0 m）,with Novosphingobium,Anaerolineaceae,etc.as the main dominant bacteria,while NH₄⁺-N degradation mainly occurred at the middle and upper parts of the UAB（1.0～2.0m）,with Nitrospira as the dominant bacteria.The enzyme gene numbers of nitrate oxidoreductase in U0.0,U1.0,and U2.0 samples were 2262,5772,6372（nxr A）,974,2684,and 3398（nxr B）,and their relative abundance distribution was similar to that of NH₄⁺-N degradation and nitrifying bacteria.The decrease in TN concentration in UAB may be closely related to the dominant bacteria genus Terrimonas.COD,NO₃^–-N,and TN were uniformly degraded along the DSB.Chloroflexi,Proteobacteria,and Bacteroides were the dominant bacteria in the DSB,and Thauera and Ignavibacterium were the dominant bacteria.