Study On The Enhancement Of Nitrate Biodegradation By Humic-like Redox Mediators

Water nitrogen pollution is a serious problem in our country.Biological denitrification has become one of the most effective methods to remove nitrogen pollution in water.It has been shown that the redox mediators(RM)can accelerate the electron transfer rate from electron donor to electron receptor and increase the reduction rate of pollutants by one to several orders of magnitude.Humic substances(HS)contains a large number of redox active groups and is a natural redox mediator.In this study,humic-like redox mediators were immobilized in mature granular sludge by granular sludge immobilization method.Humic acid(HM)and humic acid(HA)were selected as mediators and nitrate as model pollutant.In this paper,the characteristics of the media material,the operation of the reactor and the structure of the microbial community were studied,and the effects of the media on the biodegradation of nitrate in the reactor were discussed.The mature denitrifying granular sludge was successfully cultivated in the UASB reactor within 58 days after acclimation of the inoculated sludge,to meet the needs of granular sludge fixation.The settling performance of sludge was better and the reactor was running well.In the biological characteristics of sludge,Hyphomicrobium is the dominant species in the mature granular sludge.Humin(HM)was prepared by using humic substances standard material as raw material,the effect of immobilized humin on anaerobic reduction of nitrate was studied.The results showed that HM had certain redox reversibility,containing quinone,carboxyl,hydroxyl and other redox functional groups,which was beneficial to the degradation of nitrate.Compared with the control group,the nitrate degradation ability and the COD removal capacity in the UASB reactor with HM were 1.1-fold and 1.09 times higher than those in the control group,respectively.The dominant bacteria in the microflora containing HM granular sludge were significantly different from those in the blank,and the dominant bacteria at the generic level were Paracoccus(39.85%),with a difference of21.49%.Using ferrous sulphate and humic substances standard material as materials,the effect of immobilized Fe-HA on nitrate anaerobic reduction was studied.The results showed that Fe-HA contained abundant redox functional groups such as quinone,carboxyl and phenolic groups,which was beneficial to the degradation of nitrate.In UASB reactor,Fe-HA was successfully immobilized in granular sludge.Compared with the control group,the nitrate degradation ability and the COD removal ability of the reactor increased by 1.48 and 1.27 times,respectively.The dominant bacteria in the microflora containing Fe-HA granular sludge were significantly different from those in the blank,and the dominant bacteria at the generic level were Paracoccus(21.56%),and the content difference was 17.77%.