Influences Of Biochar On Biological Nitrogen Removal In Subsurface Flow Constructed Wetland

Biochar is the carbon-rich product which has been treated by high temperature under the condition of oxygen or oxygen.Most studies have shown that biochar is widely used as a soil conditioner due to the high physical stability,biochemical decomposition resistance,large specific surface area and porous structure.It can directly or indirectly affect the diversity,abundance and activity of nitrifying bacteria and denitrifying bacteria,and then affect the cycling of soil nitrogen.Based on the characteristics of biochar and the effective use of wetland plants,this study aims to harvest the plants and to add them to the constructed wetland.Using high-throughput sequencing and other molecular biology techniques,explore the mechanism of the effect of migration on wetland nitrogen transformation process of biochar from the perspective of Microbiology,reveal the effect of biochar on microbial community structure in the wetland system,to strengthen the wetland and provide a theoretical basis for nitrogen removal.A set of constructed wetlands were built under greenhouse,four different biochar addition were selected(30%,20%,10%,0%),with the influent COD:N 10:1,7:1 and 4:1.In this paper,the different biochar addition effects on denitrification and the microbial community structure in constructed wetlands were studied.The main contents and results were as following:(1)The effluent of DO was lower than 0.4mg/L in all wetlands,and the wetland was in the anaerobic state for a long time.The addition of biochar can increase the effluent of DO.When the COD:N is low,the effect of biochar on the effluent DO is significant(p<0.05).With the increase of COD:N,the effect of biochar on the effluent DO is not significant.Wetland effluent pH was significantly lower than that of the influent pH,and biochar can increase wetland effluent pH,biochar added significant influence on effluent pH(p<0.05),but the biological carbon dosage is not significant in wetland pH.The effluent pH of influent COD:N=10:1 was significantly lower than that of COD:N=4:1 and COD:N=7:1.(2)At different COD:N conditions,the COD removal rate of were over 80% in all wetlands.Biochar had a significant effect on the removal of COD in the wetland system.At different influent conditions,The removal rate of NH4+-N significantly increased at the wetland system with biochar.and the high proportion of biochar can significantly reduce the concentration of NH4+-N in the wetland system.The addition of biochar had no significant effect on NO3--N removal,and the effect on TN removal in wetland system was basically the same as that of NH4+-N.(3)The ability of extracting EPS from different extraction methods was different.The maximum efficiency can be obtained by steam extraction,and there was no phenomenon of large cell autolysis.Therefore,the steam extraction of EPS from biochar wetland was carried out in this study.The EPS component and the change law showed a significant difference at each wetland system with the addition of biochar.There are differences in the microbial metabolism.The FTIR spectra,molecular weight distribution and 3D-EEM of EPS on different packing layers were analyzed.The results of FTIR showed that the main components of EPS were similar in the each system,but the existence of individual infrared absorption peak disappeared or reduced.This further indicated that the microbial biomass was changed by the addition of biochar.results of molecular weight distribution of EPS on the biochar filler was shifted to the small molecular substances,which indicated that the characteristics of the two extracellular polymeric substances were different.The fluorescence spectrum analysis showed that there was a class of proteins and soluble microbial byproducts in extracellular polymers.(4)The results of high throughput sequencing showed that there were 51 species in the wetland samples,and Bacteroidetes,Proteobacteria and Firmicutes were the dominant bacteria in the wetland.The influence of biochar addition on dominant bacteria was not significant under COD:N=4:1.At COD:N=7:1 and COD:N=10:1,the main dominant species of bacteria were significantly different because of biochar addition in wetland system.The main nitrogen removal bacteria in wetland were Nitrosomonas,Nitrospira,Thauera,Thermomonas,Thiobacillus,Dechloromonas,Pseudomonas and Ferruginibacter strains,mainly for nitrification and denitrifying bacteria.Biochar can significantly change the structure of nitrifying bacteria and denitrifying bacteria in wetlands under different influent conditions.It can be found that the addition of biochar can significantly change the microbial population structure of the wetland system and the influence of high biochar addition is more significant by cluster analysis.