Mechanism And Application Of Iron-carbon Micro-electrolysis Coupled Biological Denitrification For Nitrogen Removal

Nitrogen pollution has become a global pollution problem.Insufficient organic carbon source is a key factor restricting the denitrification of sewage with low carbon to nitrogen ratio?C/N?.The combined denitrification of electrochemical and biological method has become a hot spot in the field of low-C/N wastewater treatment,but the denitrification mechanism needs to be further improved.Zero valent iron?Fe⁰?and iron carbon micro electrolysis system were applied to treat low C/N wastewater,and their reduction performance and mechanism were explored.By constructing an iron-carbon micro-electrolysis coupled biological denitrification?MEBD?denitrification system for the treatment of low-C/N sewage,the single-factor control variable method was used to explore the influence of dosage of iron-carbon filler?Fe-C?,denitrifying flora?DB?,and initial pH on MEBD removal of pollutants,and the MEBD denitrification conditions were optimized by response surface methodology?RSM?.High-throughput sequencing?HTS?was used to analyze the evolution of microbial communities before and after MEBD denitrification,to study the influence of iron-carbon fillers on the structure of microbial communities,and to explore the synergistic mechanism of MEBD removal of pollutants based on the kinetics of pollutant removal.The main research contents and results are as follows:?1?Study on the performance of iron-carbon micro-electrolysis treatment of low C/N sewage.The performance of zero-valent iron and iron-carbon micro-electrolysis reduction of nitrate?NO₃^--N?were investigated in the range of pH=4?7,and the effects of pH and Fe⁰/AC on nitrate removal by iron-carbon micro-electrolysis system were discussed.Under acidic conditions?pH=4?,the efficiency of the micro-electrolysis system to reduce nitrate was significantly better than that of the zero-valent iron system.The adsorption effect of activated carbon on nitric acid was weak,and the removal rate of nitrate by the micro-electrolysis system would reach 88.86%.Under neutral conditions,the nitrate reduction efficiency of zero-valent iron was only 6.84%,and the nitrate removal rate of the iron-carbon micro-electrolysis system was maintained at about 50%.When Fe⁰/AC is 3:1,the micro-electrolysis system had the best reduction effect on nitrate.?2?The single factor experiment was used to investigate the effects of Fe-C dosage?m/v?,DB dosage?v/v?,and pH on MEBD denitrification.With the increase of Fe-C dosage or pH,the removal rate of nitrate-nitrogen?NO₃^--N?by MEBD showed a trend of first increasing and then decreasing.When the Fe-C dosage and pH are 10%and 7,respectively,the removal rate of NO₃^--N in the MEBD system was the highest,indicating that the coupling system had the best denitrification effect under the condition of neutral and suitable Fe-C dosage.The denitrification effect of MEBD continued to increase with the increase of DB dosage.After the DB dosage exceeded5%,the removal rate of MEBD to NO₃^--N no longer increased significantly.It shown that adding 5%of the denitrifying flora was more conducive to MEBD denitrification.?3?Response surface methodology optimized MEBD denitrification conditions.Through Design-Expert 8.0.6,a response surface model with NO₃^--N removal rate?NDR?as the response index was established to investigate the effects of 3 main influencing factors on MEBD denitrification interactive influence.The study found that the order of the factors affecting the denitrification of MEBD was:Fe-C dosage>pH>DB dosage,and there was a significant interaction between pH and Fe-C dosage,and pH and DB dosage.The optimal denitrification conditions for MEBD were:pH=7.02,DB dosage 5.02%,Fe-C dosage 10.14%.Under the best denitrification conditions,the removal rate of NO₃^--N by MEBD reached 79.89%,indicating that MEBD had a good denitrification effect.?4?MEBD repaired low C/N polluted water bodies.Controlled experiments were used to investigate the remediation performance of MEBD on low-C/N polluted water bodies.By monitoring indicators such as pH,DO,nitrogen,and COD,the changing laws of pollutants in the process of MEBD denitrification were obtained.The removal rates of TN and COD in the MEBD group were 65.56%,44.76%,60.70%and 71.19%,36.73%,and 28.47%higher than those in the control group,DB group,and Fe-C group,respectively,indicating that MEBD had an effect on nitrogen in low-C/N wastewater.And organic matter removal effect was better.During the MEBD denitrification process,the pH maintained a continuously rising trend,indicating that denitrification was always present in the system;the DO concentration showed a trend of first rising and then falling,indicating that the atmospheric oxygen enrichment effect was strong in the early stage of the test.?5?High-throughput sequencing?HTS?was used to analyze the changes in microbial community structure in the process of MEBD repairing low C/N.Analyze the community structure of microorganisms in the water samples on the 10th day?D10?and 20th day?D20?during the MEBD restoration process by HTS,and compare with the DB microbial populations added to explore the microbial phylum,class,order,and genus levels.After MEBD restoration,the abundance and diversity of microorganisms in low-C/N polluted water bodies increased significantly.The dominant bacteria phyla included Proteobacteria,Bacteroidetes,and Chlamydiae;the dominant bacteria classes includedb-Proteobacteria,a-Proteobacteria,and Chlamydiia;the dominant bacteria genera were Runella,Flavobacterium,Dyadobacter,Acidovorax,Sediminibacterium,and Opitutus.The relative abundance of microorganisms related to organic matter degradation and nitrate reduction in the MEBD system increased significantly,indicating that micro-electrolysis could affect the distribution of microbial communities,and iron-carbon fillers could promote the evolution of microbial community structure.?6?Research on the denitrification mechanism of the MEBD coupling system.The denitrification kinetics of MEBD under different influencing factors was fitted,combined with the evolution of microbial community structure to clarify the mechanism of MEBD denitrification.Under different Fe-C dosage,DB dosage,and pH conditions,the removal of TN and COD by MEBD accorded with the first-order reaction kinetic equation.Through HTS analysis,it was found that MEBD contained part of Hydrogenophaga,which indicated the existence of autotrophic denitrification in the system.The denitrification of the MEBD coupling system mainly included four reaction processes,namely:heterotrophic biological denitrification,autotrophic biological denitrification,iron-carbon micro-electrolysis,and electrochemical reduction.The above research results show that the iron-carbon micro-electrolysis coupled with biological denitrification is of great significance for sewage denitrification,and the research can provide theoretical basis and technical support for low-C/N sewage denitrification.