Biochar Coupled Biocathode Denitrification And Its Microbiological Mechanism Analysi

After the national implementation of “Source control and emission reduction”,the organic pollution of wastewater has been effectively treated,and nitrogen pollution has become the main environmental problem.However,the traditional biological nitrogen removal technology is greatly affected by the insufficient influent carbon source,and the nitrogen removal effect is poor,and the by-products such as nitrate and nitrite are easy to accumulate.With more and more attention paid to energy shortage and environmental pollution,Microbial fuel cell(MFC)has ushered in a new research upsurge in wastewater denitrification.The biological cathode can directly provide electron to make up for the shortage of carbon source in denitrification of wastewater,solve the problem of low C/N ratio wastewater biological nitrogen removal,and avoid the secondary pollution caused by adding carbon source.At the same time,biochar is widely used in the treatment of environmental pollution because of its rich electro-active functional groups and good biocompatibility.In order to improve the treatment efficiency of MFC for wastewater with low C/N,and make up for the shortcomings of high cost and low performance of the cathode,this study took the cathode of microbial fuel cells as the research object,domesticated and selected a group of electrophilic denitrification bacteria that can use electric current as an electron donor by gradually reducing C/N,and explored its denitrification mechanism;With the help of biochar characterization,electrochemical analysis and metab characteristics by adding biochar;Use metagenomic analysis to explain its microbiology olomics analysis,the mechanism of biochar in promoting electron transfer and enhancing cathode denitrification of MFC was elucidated.The main research contents are as follows:(1)In this study,the biomass of Ampelopsis grossedentata was prepared by limiting oxygen and controlling temperature at 400 °C and 700 °C,and named as BC400 and BC700 respectively.Using anaerobic sludge as inoculum,the electrophilic denitrifying bacteria,which can be supplied by electric current,can be acclimated and enriched by gradually reducing carbon source,and the stable denitrification efficiency of MFC can reach 45%.Subsequently,biochar was added to the reactor and the removal rate was further increased to 60% after a period of time.At the same time,the optimal initial concentration of ammonia nitrogen,the optimal p H value and the optimal biochar dosage were 100 mg/L,7 mg/L and 0.5 g/L,respectively,the nitrogen removal efficiency of low-temperature biochar was better than that of high-temperature biochar,and the highest removal rate of ammonia nitrogen was 67% in 24 hours.Moreover,the bio-carbon-MFC cathode system also has good purification effect to the complex actual domestic sewage.The removal rate of COD,total nitrogen,ammonia nitrogen and SND were 81.36% ～92.29%,54.78% ～ 65.20%,79.00% ～ 96.23% and 80.31% ～ 97.81%,respectively.(2)Metagenomic sequencing analysis of MFC cathode microbes showed that the community diversity and homogeneity of denitrifying bacteria in the experimental group(BC400,BC400＿700,BC700)were higher than those in the control group(CK).The dominant phyla in the four groups were Proteobacteria,Chloroflexi,Actinobacteria,Bacteroidetes and Euryarchaeota.Proteobacteria were the dominant phyla,and their proportions in the four groups were more than 70%,and there was no significant difference between the four groups(P >0.05).The amount of Campylobacter was significantly reduced in the experimental groups.The dominant bacteria in the experiment group(>6%)were unclassified＿Betaproteobacteria and unclassified＿Rhodocyclales,while the dominant bacteria in the CK group(> 6%)were unclassified＿Chloroflexi and Phenylobacterium.(3)The functional genes of denitrifying bacteria in four groups were analyzed.The results showed that there were significant differences in denitrifying genes among the four groups(0.01< P < 0.05).Compared with the control group,the relative abundance of nir SK and nos Z increased by 1.5 ～ 3 times in the experimental group.Amo,Hao and so on also had higher abundance in the experimental group,but almost could not be detected in the CK group.The results showed that biochar could create suitable microenvironment for nitrite-oxidizing bacteria(NOB)and ammonia-oxidizing bacteria(AOB)and accelerate nitrification in the process of nitrogen removal.In addition,biochar enhances nitrate removal in heterotrophic denitrification systems by promoting organic matter degradation,accelerating electron transfer rates,and enhancing the activity of related enzymes.(4)The results of biochar characterization showed that both BC400 and BC700 had honeycomb-like pore structure with obvious voids;BC400 contains a large number of oxygen-containing active functional groups,thus providing more exchange sites for electrons and nutrients,BC700 aliphatic carbon levels are significantly reduced,and biochar forms a relatively stable aromatic ring structure.Cyclic voltammetry(CV)curve analysis showed that the electron exchange ability of BC400 group was better than that of BC700 group.The analysis of microbial secretions showed that the main functional groups in the electron mediator secreted by microorganisms were benzene ring,carbonyl group and nitrogen heterocyclic ring,it is hypothesized that biochar may further affect the electron transport of electro-denitrifying bacteria by affecting microbial secretions such as aromatic proteins.