The Mechanism Of Enhanced Biodegradation Of Halophenols By Nitrate

This study constructed an anoxic denitrification system by adding sodium nitrate as electron acceptor,to enhance the biodegradation of halophenols（HPs）.Furthermore,this study explored the degradation performance of HPs,the stability of long-term operation,the evolution of microbial communities,and the degradation mechanism of HPs under anoxic conditions,in order to provide technical support and theoretical basis for the industrial bio-enhanced treatment of HPs wastewater.The specific contents of this study were as follows:This experiment developed a continuous flow anoxic denitrification system based on activated sludge system by adding sodium nitrate as electron acceptor and choosing 4-bromophenol（4-BP）as the target pollutant.In addition,the system without sodium nitrate was used as the anaerobic control system.This study mainly explored the stability of long-term operation,the microbial community evolution and 4-BP mineralization mechanism of the anoxic denitrification system.The results of this research showed that when the hydraulic retention time,the influent p H and the influent Na NO₃ concentration were controlled at 24 h,7.0 and 0.7 m M,0.87 m M 4-BP could be removed completely in the anoxic denitrification system.Besides,the total organic carbon（TOC）removal efficiency was above 90%,and the nitrate reduction efficiency was higher than 96%.However,the 4-BP removal efficiency was always lower than 35%in the anaerobic control system.Microbial community analysis indicated that the addition of nitrate promoted the enrichment of denitrifying functional bacteria genera（norank-f-OLB14,Denitratisoma and so on）,electron transport functional bacteria genera（Ignavibacterium）,dehalogenation bacteria genera（norank-f-Candidatus Peregrinibacteria,Candidatus Protochlamydia and so on）,aromatic degradation bacteria genera（norank-f-SBR1031,Limnobacter and so on）,which enhanced the degradation and mineralization ability of 4-BP.Base on the identification of intermediate products and degradation pathway,it was founded that 4-BP might undergo a ring cleavage reaction firstly,followed by an oxidative dehalogenation to produce carboxylic acid intermediates and then enter the tricarboxylic acid（TCA）cycle.In order to further explore the influence of different halogenated groups on the degradation performance of HPs in the anoxic denitrification system,4-iodophenol（4-IP）,4-chlorophenol（4-CP）,4-fluorophenol（4-FP）were selected as the target pollutants to explore the effect of different halogenated groups on degradation performance,microbial community evolution,and mineralization mechanism in the anoxic denitrification system.The results showed that 0.87 m M 4-IP and 4-BP could be completely removed,whereas the removal efficiencies of 4-CP and 4-FP were about 70%and 40%,respectively.The microbial community structure analysis showed that the evolution of microbial community in the reactor which degraded 4-FP was significantly different from that in the reactors which degraded 4-IP,4-BP,4-CP,respectively.Most of the dominant bacteria genera in the4-FP reactor were not detected in the reactors that degraded 4-IP,4-BP,and 4-CP.In addition,the microbial community evolutions were relatively similar in the reactors that degrade 4-IP,4-BP and 4-CP.Based on the identification of intermediate products and the analysis of degradation pathways,it was found that the degradation pathways of HPs containing different halogenated groups were similar under denitrification conditions.HPs might undergo a ring cleavage reaction firstly.Among them,4-IP’s ring cleavage occurred at the meta position of the hydroxyl group,and that of 4-BP,4-CP and 4-FP occurred at the ortho position of the hydroxyl group.The ring-opened product then underwent an oxidative dehalogenation reaction to product carboxylic acid intermediates,which then entered the TCA cycle.