Effects And Mechanisms Of Sulfamethoxazole On Denitrification And Hydrogen Production From Excess Sludge Anaerobic Fermentation

Antibiotics have played a major role in the treatment of diseases,but most antibiotics cannot be fully absorbed and utilized by organisms,and these antibiotics eventually enter WWTPs along with sewage.At present,activated sludge process is still the mainstream denitrification process in WWTPs,but the antibacterial property of antibiotics may affect the regular operation of denitrification process.In addition,due to the adsorbability of activated sludge,a large amount of excess sludge rich in antibiotics will be generated during the wastewater biological treatment.Therefore,the subsequent biological treatment of excess sludge may be affected.What’s more,antibiotics may cause the risk of transmission of antibiotics resistance bacteria and antibiotics resistance genes.Therefore,it is of great significance to explore the influences of typical antibiotics on denitrification and anaerobic fermentation processes,as well as the microbial community.In this study,one SBR without SMX domestication was constructed to cultivate denitrifying bacteria not adapted to SMX,and another SBR with SMX long-term domestication was constructed to cultivate denitrifying bacteria adapted to SMX.Subsequently,batch experiments were conducted to investigate the effect of SMX on the denitrification process under non-adaptive and adaptive conditions.The results showed that SMX had no obvious influence on the degradation of NO₃^--N,but significantly inhibited the degradation of NO₂^--N and N₂O-N under non-adaptive condition.While under adaptive condition,the degradation of NO₃^--N,NO₂^--N and N₂O-N were markedly inhibited by SMX.Regardless of non-adaptive or adaptive conditions,SMX stimulated the release of N₂O-N notably during the denitrification process.In addition,the denitrification performance of the two SBR reactors was compared.It was found that the NO₂^--N and N₂O-N were accumulated badly in the SBR domesticated with SMX.It was found that SMX suppressed denitrification mainly by restraining microorganisms secreting EPS and forming micelles,as well as weakening the electron transport system activity.Microbial community analysis illustrated that SMX increased the relative abundance of incomplete denitrifying bacteria such as Thaurea and Acinetobacter,and reduced the relative abundance of denitrifying bacteria such as unclassified＿f＿＿Comamonadaceae,Pseudomonas,Paracoccus,Flavobacterium,resulting in the decline of denitrification performance and accumulations of NO₂^--N and N₂O-N.The SMX adsorbed by activated sludge would enter the stage of subsequent sludge resource utilization.Therefore,this study further explored the effect of SMX on hydrogen production from anaerobic fermentation of excess sludge under alkaline condition.The results showed that the yield and production rate of H₂ were both elevated by SMX.Mechanism study revealed that SMX promoted the activity of hydrolases（proteases andα-glucosidase）and the degradation of bovine serum albumin,so SMX was conducive to the hydrolysis stage and producing small molecular organic matter.SMX also promoted the activity of acetate kinase and the production of volatile fatty acids,suggesting that SMX accelerated the acidification stage,thus more H₂ was produced.At the same time,SMX inhibited the activity of coenzyme F₄₂₀ and the degradation of sodium acetate,so SMX inhibited the methanation stage and reduced H₂ consumption.According to the results of 16S r RNA,SMX increased the relative abundance of hydrogen-VFAs producers（Proteiniborus,Erysipelothrix,Tissierella,Acetoanaerobium）.