Study On The Transformation Rule And Influence Behavior Of Sulfamethoxazole In The Advanced Nitrogen Removal Process Of PHBV Biofilter

The global consumption of antibiotics continues to increase in clinical,animal husbandry and aquaculture,resulting in their widespread presence in environmental media.Overuse and improper disposal of antibiotics have allowed them to accumulate in municipal sewage systems.At the same time,the discharge of nitrate in sewage treatment plants is one of the main causes of nitrogen pollution in water,which may cause eutrophication of water and threaten human health.At present,denitrifying biofilter is a hot research and application in the field of advanced wastewater treatment.It is mainly used to solve the problem that the total nitrogen content in secondary effluent of sewage treatment plant exceeds the standard due to the high nitrate content.In denitrifying biofilter denitrification system,organic carbon source is the key factor of antibiotic bioconversion and influencing behavior.However,compared with traditional liquid carbon sources,the transformation rule and influence effect of antibiotics in the new polymer solid phase carbon source-biofilter are not clear and the internal mechanism is not clear.This project intends to select the typical antibiotic-sulfamethoxazole（SMX）as the research object,focusing on the change trend of removal rate and biotransformation process of SMX in the solid phase carbon source-polyhydroxybutyrate valerate（PHBV）denitrifying biofilter,so as to clarify its transformation rule in the system.The effects of SMX on the denitrification effect of the system were investigated by exploring the changes of different nitrogen concentrations in the produced water.Furthermore,the characteristics of microbial community structure,the expression level of denitrifying functional genes and the abundance level of resistance genes were analyzed to reveal the internal cause of antibiotics’influence on denitrification process.The research results of the project can provide theoretical basis and data support for the risk control of antibiotics in sewage treatment system.The main conclusions are as follows:（1）When the influent SMX concentration is up to 1000μg·L^-1,the average removal rate of SMX is 56.80±6.02%;Furthermore,the average removal rate of SMX was up to 81.70±6.08%when HRT was extended for 30 h.However,with the nitrate concentration increasing to 30 mg·L^-1 and 50mg·L^-1,the average removal rates of SMX decreased to 75.57±6.49%and 34.50±19.69%,respectively.These results indicate that PHBV denitrifying biological filter can effectively remove SMX.HRT and nitrate concentration are the key factors affecting SMX removal.Further,through LC-MS analysis and identification results,the main pathway of SMX removal was biodegradation,and the main intermediate degradation products were C₁₀H₁₃N₃O₃S and C₁₀H₁₁N₃O₃S.（2）When the influent SMX concentration is up to 1000μg·L^-1,the average nitrate removal rate of PHBV denitrifying biofilter is 95.96±2.67%;The results showed that SMX did not inhibit the nitrogen removal effect of PHBV denitrifying biofilter.With the increase of influent nitrate concentration,the PHBV denitrifying biofilter still maintained a good denitrifying nitrogen removal rate,with an average of 39.00±2.57 g N·m^-3·d^-1.It shows that nitrate has obvious competitive advantage when nitrate and SMX coexist.（3）Compared with the PHBV denitrifying biofilter without SMX,Alpha diversity analysis showed that long-term exposure to SMX reduced the microbial diversity of PHBV denitrifying biofilter.The dominant bacteria in PHBV denitrifying biofilter include Gammaproteobacteria,Bacteroidia and Anaerolineae,etc.Among them,the most dominant class Gammaproteobacteria can secrete extracellular polymers well,which may be an important reason why PHBV denitrifying biofilter can adapt to the presence of SMX.Furthermore,compared with Dechloromonas,the dominant denitrifiers in the PHBV biofilters without SMX were Longilinea and Leptolinea.However,the dominant denitrifying bacteria with SMX addition are Denitratisoma and Azospira.This indicated that SMX significantly changed the microbial community structure characteristics of PHBV denitrifying biofilter.（4）Furthermore,the longitudinal characteristics of microbial structures of PHBV denitrifying biofilters at genus level were significantly different.The results showed that compared with the inoculated sludge,the abundance of denitrifying functional genes in PHBV biological denitrifying filter was greatly increased.At the same time,the abundance of denitrification functional genes was mainly concentrated in the middle and lower part of the filter（0-30cm）,and the accumulation ratio of abundance was 27.90%,26.50%and 11.09%,respectively.Similar to the characteristics of denitrifying functional genes,the abundance of resistance genes was mainly concentrated in 0-30cm,and the accumulative proportions were 14.72%,26.57%and 24.20%,respectively.These results showed that there was a positive correlation between denitrifying genes and resistance genes.