Modified Biochar-enhanced Denitrification Process And Functional Analysis Of Key Bacterial Populations

With increasing eutrophication in water bodies and increasingly stringent standards for wastewater denitrification,the development of efficient biological denitrification technologies is once again a hot research topic.The use of biomass charring to prepare bio-enhanced carriers for the removal of nitrogenous substances from water not only reduces the pressure on wastewater denitrification systems,but also has a wide range of sources and good adsorption properties,showing great potential in the control of water pollutants.In this study,maize straw biochar was modified by pore regulation and functional group regulation,and the best biochar carrier was selected by examining the electron transfer activity and denitrification efficiency of different modified biochars to construct a modified biochar carrier to enhance the denitrification process applied to the denitrification of low carbon domestic wastewater.The diversity and functional roles of the main denitrifying bacteria in the bioreinforced process were analyzed to provide a theoretical basis and technical support for the upgrading and development of the enhanced denitrification and disposal process using biomass char materials.The main findings of this study are:（1）Corn stover biochar was prepared under low-temperature pyrolysis at 300°C,modified by pore modulation and functional group modulation,and characterized by scanning electron microscopy,N₂ adsorption and desorption isotherms,and FTIR.The study of enhanced biological denitrification by different modified biochar was examined,and the nitrate removal rate of the reactor with alkali-modified biochar was60.84%,which was significantly higher than that of the control group（29.08%）.（2）Combining molecular biology and electrochemical indicators,it was found that the addition of alkali-modified biochar enhanced the electron transfer activity（EDSA）,nitrate reductase（NR）,and nitrite（NIR）reductase activities of the microorganisms by91.8%,17.06%,and 47.1%,respectively,thus enhancing denitrification.High-throughput sequencing revealed that with alkali-modified biochar injection promoted Proteobacteria（19.29%）,Firmicutes（35.43%）,Chloroflexi（6.7%）,Bacteroidetes（5.88%）,and Actinobacteriota（3.35%）and other related denitrifying bacteria became the dominant species in the reactor,eventually changing the microbial community structure and promoting the rapid denitrification reaction.（3）Construction of a sequential batch enhanced denitrification system using alkali-modified biochar,where denitrification efficiency is virtually independent of influences of influent shock load（C/N=5-11）,hydraulic retention time（HRT=6-10h）and p H（5-9）,maintaining a consistent 90%nitrate-nitrogen removal rate at all times.The system operated in the range of decreasing C/N from 8 to 3 over a long period of time.Compared to the control group,the enhanced system achieved ideal removal of total nitrogen（90%）and nitrate nitrogen（90%）at C/N=5,and the removal efficiency of total nitrogen and nitrate nitrogen was still nearly 10%higher than the control group at influent C/N=3.（4）The lactate dehydrogenase（LDH）activity was almost 25%lower in the biofortified group that was dosed with the modified biochar than in the control group,and the microorganisms had better cell membrane integrity and less cellular decay,thus enhancing microbial abundance.Similarly,enhanced reactors in which biochar is injected into the sequential batch reaction can similarly increase microbial EDSA,NR,and NIR activity,thereby facilitating denitrification treatment.Reactors in which biochar is added to the sequential batch reaction also increase the microbial activity of EDSA,NR,and NIR,thus facilitating the treatment of denitrification.The relative abundance of relevant denitrifying microorganisms such as Proteobacteria,Chloroflexi,Bacteroidetes,and Actinobacteriota in the reinforced reactor increases,which in turn promotes the effectiveness of microbial denitrification in a low carbon-to-nitrogen ratio environment.