Multistage A/O Combined With Deep Bed Filter Process Treating Municipal Wastewater:Performance And Microbial Characteristics

Recently,multistage anoxic/aerobic（AO）process due to the high carbon source utilization rate and perfect nitrogen and phosphorus removal has been applied in urban sewage treatment in China.However,the relevant achievements were only discussed from the angle of process variant and effect for meeting level A discharge standaid.However,less reports were on achieving high discharge standard（COD≤30 mg/L,TN≤10 mg/L and TP≤0.3 mg/L）and characteristics of microbial community.Therefore,in this study,the operation characteristics of multistage AO process were studied,and discussed the advanced nitrogen removal performance of deep bed filter with pre-phosphorus removal.Meanwhile,a combined process of multistage AO and deep bed filter was constructed,and its efficiencies in treating low temperature and low C/N ratio wastewater were discussed.Besides,the measures for enhancing denitrification were discussed.Finally,microbiology was used to reveal the characteristics of functional microflora and response characteristics of the combined process.At room temperature,the operating characteristics of multistage AO process and the effects of various influencing factors on pollutant removal efficiency were investigated by single-factor test.Besides,a deep bed filter with pre-phosphorus removal was proposed,and the mechanism of pollutant removal was analyzed.The results showed that the multistage AO process owned excellent pollutant removal performance,and could meet high discharge standard with low attainment rate.After adding advanced treatment process,the effluent could reach the standard steadily.Under the optimum operating conditions,the effluent concentrations of COD,TN and TP from multistage AO combined advanced treatment process were 19,7.59,and 0.14 mg/L.Based on the analysis of pilot operation,the cost of advanced treatment increased by 0.229 yuan/t.Fe²⁺/S₂O₈^2-system could effectively remove TP and total organic matters from secondary effluent,and the reaction fitted the first-order kinetics equation.TP was precipitated by Fe₄（PO₄）₃（OH）₃,and the macromolecular compounds such as protein compounds were degraded by HO?and SO₄^-?,which produced from Fe²⁺/S₂O₈^2-system.TN was removed from denitrification deep-bed filter.The miximal removal rate was in the middle of the filter,and the removal rate was proportional to the biomass.Low temperature and low C/N influent affect the biological nitrogen removal.In order to ensure the multistage AO combined process to meet high discharge standard steadily under above conditions,the effects of low temperature and low C/N influent on multistage AO and deep bed filter process were studied,and the measures to strengthen nitrogen removal were proposed.The results showed that the average concentrations of COD,TN and TP in effluent of the combined process were 16,7.78 and 0.20 mg/L by optimizing the operation and filling 10%suspended packing in multistage AO process,and prolonging the empty bed residence time（EBCT）of deep bed filter under low temperature.Under the condition of low C/N ratio,the utilization rate of carbon source could be improved by optimizing parameters,but it could not meet the discharge requirements.By adding carbon source（C/N was 5⁶）,the effluent concentrations of TN and TP from combined process were 10 and 0.3 mg/L.To reveal the mechanism of pollutant removal,the characteristics of functional microflora in multistage AO combined advanced treatment process were analyzed by high throughput sequencing.The results demonstrated that A/O alternation in multistage AO process resulted in the differences in microbial community abundance and metabolic function among different functional units,but the diversity was fewer changes.The proportion of influent and the reflux of mixed liquor significantly affected the abundance of organic matter degradation and denitrification functional bacteria in anaerobic and anoxic areas.Low temperature promoted the enrichment of low-temperature-resistant bacteria.Nitrogen removal by multistage AO process was enhanced by suspended packing,which improved the abundance of nitrogen removal bacteria in aerobic zone.Meanwhile,the competition of nitrification was enhanced in nitrogen removal metabolic network,further improved the removal efficiency of TN.In deep bed filter,the abundance of Blastocatellaceae_Subgroup₄ and JG30-KF-CM45 ranged from 6%to 10%,and the other flora abundance fluctuated between 2%and 5%.The abundance and functional characteristics of functional flora showed that the middle part was higher than two ends.This study explored to provide theoretical and technical support for the popularization and application of multistage AO process.