Removal Of Phosphorus And Nitrogen From Urban Sewage With Biofilm-Electrolytic Coupling System

The existing small-scale urban sewage treatment equipment had a long process flow,complex chemical phosphorus removal operation and management,and for low C/N wastewater,there was insufficient carbon source for denitrification.To solve the above problems,a single-stage biofilm-electrolysis coupling treatment technology for urban sewage was proposed.The goal was to develop small-scale,efficient and low-cost urban sewage treatment equipment,the research objects were sequential batch biofilm-electrolysis coupling system and continuous flow biofilm-electrolysis coupling system.The effects of urban sewage packing density and electrode layout on the construction of biofilm-electrolysis coupling system were explored.16S rRNA Amplicom sequencing was used to analyze the microbial population in the construction system,and the microbial mechanism of denitrification was explored.The effects of DO,operating conditions and current intensity on the efficacy of biofilm-electrolysis coupling system were investigated.With the best working condition parameters,we focused on exploring the pollution removal efficiency of the biofilm-electrolysis system for low C/N urban wastewater treatment.The main conclusions of the study were as follows:Filler density and electrode layout had a significant effect on the construction of urban sewage batch biofilm-electrolysis coupling system.Compared with the filler density 30 g/L,the system with filler density 40 g/L had TN removal rate increased by3.98%;Compared with the dual-cathode layout system and the single-cathode layout system,the TN removal rate of the three-cathode layout system increased by 3.02%and6.67%,respectively.With DO 6.05 mg/L,and a current intensity of 0.1A,the system was successfully constructed in 32 days.The removal rates of NH₄⁺-N,TN,TP,and COD were 99.39%,86.10%,98.49%and 91.05%.According to 16S rRNA Amplicom high-throughput sequencing results,In the construction system,the dominant functional genus of includes heterotrophic nitrification-aerobic denitrification bacteria Acinetobacter.Autotrophic nitrifying bacteria genus Nannocystis and Nitrospira.Heterotrophic denitrifying bacteria Rhodococcus and Bacillus.Hydrogen Autotrophic Denitrifying Bacteria Paracoccus,Hydrogenophaga,Pseudomonas,Thauera.Iron autotrophic denitrifying bacteria Azospira.The system realized denitrification through coupling of multiple denitrification paths.DO,operating conditions and current intensity effected significantly for the sequential batch biofilm-electrolysis coupling system to treat urban sewage.Compared with the DO was 4.05±0.43mg/L,When the DO was 4.05±0.43mg/L,the NH₄⁺-N,TN and COD removal rate was increased by 10.89%,6.59%and 2.8%,respectively.When the current intensity gradually decreased from 0.1A to 0.02A,the system removal rate of TN gradually increased from 86.54%to 94.04%.Under the better operating parameters,effluent NH₄⁺-N,TN,TP and COD of the system was 0.17 mg/L,2.55 mg/L,0.13 mg/L and 30.36 mg/L,and the removal rates was 99.60%,94.09%97.41%and 90.30%,respectively.The effluent quality was obviously better than the standard of class A.The batch biofilm-electrolysis coupling system had high treatment efficiency to treat low C/N urban sewage.Anoxic HRT had a significant effect on the treatment efficiency of the low C/N coupling system.When the anoxic HRT was 8h and the aerobic HRT was4h,the coupling system had better pollution removal efficiency.When the urban sewage C/N was 3.5±0.3,2.5±0.3,1.5±0.3,the effluent NH₄⁺-N and TP of the coupling system had no obvious difference.Effluent NH₄⁺-N was 0.33 mg/L,0.32 mg/L and 0.29 mg/L,respectively.Effluent TP was 0.11 mg/L、0.09 mg/L、0.07 mg/L,respectively.The TN concentration of the effluent was 5.06 mg/L,5.63 mg/L and 6.69 mg/L,which gradually increased as the C/N decreased.The effluent COD concentration was 19.21 mg/L,12.35mg/L and 9.93 mg/L,which gradually decreased as the C/N decreased.Under different C/N,the effluent quality was obviously better than the standard of class A.At a temperature of 26-28℃,the DO concentration was 4.05±0.43 mg/L,the current intensity was 0.02A,the packing density was 40 g/L,and the electrode arrangement was three-cathode arrangement,the reactor was successfully operated for 26 days to construct a continuous flow biofilm-Electrolysis coupling system.The removal rates of NH₄⁺-N,TN,TP and COD was 99.26%,87.32%,97.95%and 93.80%,respectively.According to16S rRNA Amplicom high-throughput sequencing results,in the constructed system,dominant genus of denitrifying bacteria including autotrophic nitrifying bacteria Other＿f＿Nitrosomonadaceae,Other＿f＿Pirellulaceae,Nitrospira.Heterotrophic nitrification-aerobic denitrifying bacteria Acinetobacter.Heterotrophic denitrifying bacteria Other＿f＿Comamonadaceae,Comamonas.Denitrifying phosphorus accumulating bacteria Dechloromonas.Hydrogen autotrophic denitrifying bacteria Paracoccus、Pseudomonas.The system realized denitrification through coupling of multiple denitrification paths.DO and current intensity had significant effects on the efficiency of pollution removal in continuous flow biofilm-electrolysis coupling system to treat urban sewage.With a DO of 4.05±0.43 mg/L,the removal rates of NH₄⁺-N,TN,and COD was increased by 17.18%,7.11%and 3.69%respectively.With a current intensity of 0.015A,the removal rate of TN and TP was increased by 3.66%and 8.69%respectively when the current intensity was 0.01A.Under the better operating parameters,effluent NH₄⁺-N,TN,TP and COD of the system was 0.28 mg/L,5.58 mg/L,0.09 mg/L and 28.64 mg/L,and the removal rates was 99.13%,86.87%,98.24%and 90.85%,respectively.The effluent water quality was significantly better than the water quality standard of class A.The continuous flow biofilm-electrolysis coupling system had high treatment efficiency to treat low C/N urban sewage.Under the better operating parameters,the coupling system with C/N of 3.5±0.3 and 1.5±0.3,the effluent NH₄⁺-N,TN,TP and COD concentrations were 0.34 mg/L,8.54 mg/L,0.10 mg/L,17.36 mg/L and 0.32 mg/L,18.26mg/L,0.09 mg/L,9.93 mg/L,respectively.Met the water quality standards of class A and class B standards,respectively.