Effect Of Cathodic Enhancement On BES Hydrogenotrophic Denitrification Process

Due to the development of industry and animal husbandry,nitrate pollution entering lakes,rivers,groundwater and other water bodies,not only causes eutrophication of water bodies,but also seriously affects land and human life safety.From this perspective,how to effectively deal with nitrate pollution becomes an urgent problem.In recent years,the nitrate wastewater denitrification technology using BES?bioelectrochemical system?not only retains the advantages of biological methods,but also combines the advantages of electrochemical systems with high efficiency and waste resource utilization.Therefore,it has become an emerging technology for nitrate pollution treatment.Based on hydrogen autotrophic denitrification BES,this study focused on the enhancement of denitrification of biocathode through cathode enhancement methods such as polarity inversion and PPy?polypyrrole?modification.Four groups of BES reactors were set up:control group,PPy modified group,polarity inversion group and PPy modified polarity inversion group.Meanwhile,electrochemical analysis such as EIS?Electrochemical Impedance Spectroscopy?and CV?Cyclic Voltammetry?were used to determine the effect of cathode strengthening on the electrochemical performance of BES cathodes.Also,degradation rates of nitrate nitrogen and nitrite nitrogen of each group were compared by chemical analysis.The effects of cathodic strengthening on the morphology of the microbial membrane were analyzed by SEM?scanning electron microscope?and LSCM?laser confocal?techniques.At the same time,indicators such as NADH?reduced coenzyme??,NOS?NO synthetase?,and hydrogen production were also measured for further exploration of the physiological and biochemical processes of denitrification.Finally,molecular biology analysis was performed,and high-throughput sequencing and PICRUSt?Phylogenetic Investigation of Communities by Reconstruction of Unobserved States?were used to further demonstrate the changes of microbial community during cathodic strengthening of denitrification.The electrochemical,denitrification performance and microbial community structure and function of the four BES groups were compared and analyzed.The main results are as follows:?1?Comparing the denitrification process of the four groups of BES,it was found that the nitrate removal efficiency of the PPy inversion group,the PPy group,the inversion group and the control group reached 95%on the 6,7,8 and 11 days,respectively.In addition,the anode COD removal rate of the PPy group reached 81.8%after the reactor was operated for three days during this period,while the control group reached only 67.4%.?2?Coulomb efficiency of the four groups reached 57.5?control?,74.6?inversion?,75.8?PPy?,and 82.1%?PPy+inversion?,respectively.As for the closed area of CV curves,impedance and capacitance of the four groups of reactors,the PPy inversion group is the optimal,since the closed area and capacitance are the largest,and the impedance is the smallest.?3?Compared with the control,the density of microbial aggregates of the inversion group was intensifier.The cathode of the PPy modified group covered a large-area multi-layered sheet biofilm,while the biofilm density was much thicker than other three groups.For LSCM imaging,the protein abundance of the PPy modified cathode was significantly higher than that of the polarity inversion cathode,and the highest protein abundance was observed on the PPy inversion cathode.Presumably,that the two strengthening methods have synergistic enrichment?4?Measurement of NADH concentration indicated that the higher the NADH concentration in the experimental group,the higher the denitrification efficiency of the system.Besides,activity of NOS was PPy+inversion group>PPy group>inversion group>control group.Moreover,it was found that the inflection points of the NO synthase activity curve in the control and PPy groups are related to the inhibitory effect of NO₂^-.Considering the hydrogen autotrophic denitrification system in this study,the hydrogen content in the gas collected by each experimental group is relatively low.?5?Through Illumina high-throughput sequencing and OTU analysis,it was found that the PPy group and the PPy inversion group contained more microorganisms related to nitrite reduction and electroactive species.As for the microbial community structure of each group,the microbial community of the PPy inversion group vaired greatly compared to other groups.The highest microbial abundances on the PPy inversion-enhanced biocathode mainly includes electrical activity,denitrification,and hydrogen autotrophy microorganisms,such as Proteiniphilum?93.1%?,Fusibacter?87.2%?,Aminiphilus?82.6%?,Desulfovibrio?81.3%?and vadinBC27-wastewater-sludge group?80.8%?.?6?PICRUSt analysis confirmed that the functional inversion genes in the polarity inversion group were dominant,while the PPy inversion group was specialized in coenzyme transport metabolism,cell membrane development,and EET?extracellular electron transfer?.Taking into account functions of the microbial communities in each group,the PPy inversion group was observed significant changes compared with other groups,indicating that cathodic strengthening can effectively enrich the viable hydrogen autotrophic denitrification population.