| In recent years,surface runoff and other non-point source pollution has become one of the main causes of eutrophication of receiving water.Aiming at the problem of nitrogen pollution in surface runoff,it constructed a sulfur/limestone autotrophic denitrification system in the submerged area zone of the bioretention to investigate the denitrification performance and the microbiological community.It would provide design guidance and theoretical reference for the nitrogen removal performance of bioretention in urban surface runoff treatment.The results of batch experiments showed that the sulfur autotrophic denitrification reaction accorded with the first-order reaction kinetics and the kinetic parameters were0.0576/h-0.0752/h.The reaction was the fastest with the kinetic parameter of0.0752/h when the mass ratio of sulfur to limestone was 1:1.Better denitrification performance could be achieved when the particle size of sulfur particles was 0.9-5.0mm.The time required for complete degradation of NO3--N was prolonged as the initial concentration of NO3--N increased.The reaction column was constructed to carry out the experiment of sulfur autotrophic denitrification in the submerged area zone of the bioretention.The results showed that denitrification mainly occurred during drying period and the removal rate of NO3--N could reach 91.5%when the initial concentration of NO3--N was 30mg/L and the drying period was 3 days.The denitrification performance was above 95%with the extension of drying period.During the drying period,the sulfur autotrophic denitrification conformed to the first-order kinetics with the kinetic parameters of0.0234/h and 0.0449/h.The sulfate concentration was slightly higher than the theoretical value and the p H was stable around neutral during the reaction process.Denitrification hardly occured during the wetting period,the volume of the submerged area zone was the amount of water that could be processed by the boretention.In the actual project,the denitrification performance of the boretention could be improved and the leakage of NO3--N could be reduced by increasing the volume of the submerged area zone.The time required for complete degradation during drying period was extended as the concentration of NO3--N increased from 20mg/L to 50mg/L.However,the final removal rate of NO3--N could reach above 97%after 5 days of drying period.The denitrification rate was the fastest when the depth of the submerged area zone was 45cm under the condition that the initial concentration of NO3--N was 20,30,40 and 50mg/L,and the microbial activity was the highest in the middle layer of the reaction column.High-throughput sequencing analysis on the filler samples showed that Thiobacillus was the main functional bacteria in the denitrification system,with a relative abundance ratio of more than 60%.In addition to Thiobacillus,a variety of denitrification-related bacteria such as Rhodanobacter,Thermomonas and Defluviimonas were detected in the system. |
