Degradation Of Sulfamethoxazole In A Nitrifying Sludge System And Fate Of Resistance Genes

Antibiotic wastewater is a kind of organic wastewater containing refractory organics and biologically toxic substances.It has the characteristics of strong biological inhibition,poor biodegradability,and high treatment cost.Due to the low treatment efficiency of antibiotic wastewater by traditional biological methods,the biological treatment of antibiotic wastewater has become a major problem to be solved in the field of wastewater treatment.At the same time,the long-term antibiotic toxicity pressure promotes the proliferation of antibiotic-resistant bacteria and resistance genes(ARGs)in the wastewater biological treatment system,which brings serious ecological safety risks and health risks.In addition,ARGs will transfer and spread between different bacterial genera in the biological wastewater treatment system.At present,the study on the fate and transfer mechanisms of ARGs during the biological treatment of antibiotic wastewater is relatively lacking.The aerobic nitrification sludge system can be used as an effective means for the removal of antibiotics and other refractory pollutants.In this study,the removal process of the sulfonamide antibiotic(sulfamethoxazole)was studied.The changes of microbial communities and functional genes were explored and the effect of antibiotic on the nitrification sludge system was determined.In addition,the removal efficiency of sulfamethoxazole by the nitrification sludge system and the role of microorganisms in the antibiotic removal process were explored,and the mechanism of antibiotic removal was clarified.At last,the fate of ARGs under different operating conditions were explored,and the mechanisms of ARGs were determined by investigating the contributions of mobile genetic elements and microbial community structure to the changes of abundance of ARGs.The main contents and conclusions are as follows:(1)The effect of antibiotics on the nitrification systemIn this experiment,a nitrifying SBR system was constructed to treat sulfamethoxazole wastewater with different concentrations(0.1,1,10 mg/L),and the effects of sulfamethoxazole on performance of the system were investigated.The results showed that: in the initial stage,the removal of COD and ammonia nitrogen was inhibited,the sludge growth rate slowed down,the sludge sedimentation property became worse,and the uniformity of the biomass and species distribution in the sludge was reduced with the addition of sulfamethoxazole.The results showed that the addition of sulfamethoxazole has a certain impact on the operating efficiency of activated sludge,and the higher the concentration of sulfamethoxazole,the greater the impact.After a period of adaptation period of the system,the sludge activity gradually recovered: the growth rate of sludge was accelerated,the sedimentation was improved.The removal rate of COD and ammonia nitrogen recovered to normal levels.(2)Antibiotic removal mechanism and the fate and transfer mechanisms of ARGsThe removal mechanism of antibiotics in the nitrification sludge system was clarified.In the early stage of the reaction,the removal efficicency of sulfamethoxazole was not high,but as the reaction proceeded,the removal efficicency of sulfamethoxazole increased significantly.The abundance of sulfamethoxazole-degrading bacteria such as Thauera,Azoarcus,increased greatly with the increase of the concentration of sulfamethoxazole,and the increase of the abundance of the gene encoding ammonia monooxygenase promoted the synthesis of ammonia monooxygenase,which enhanced sulfamethoxazole degradation by co-metabolism.Therefore,the enrichment of both sulfamethoxazole degrading bacteria and increase of ammonia monooxygenase synthesis together strengthened the removal of sulfamethoxazole.In addition,the transfer mechanisms of ARGs were studied,q-PCR and 16 S r RNA high-throughput amplification sequencing technology and statistical results showed that: both horizontal transfer and host bacterial changes(Methylotenera,Zoogloea,Sphaerotilus)resulted in the changes in the abundance of sul1 gene,and the changes in host bacteria(Brevundimonas,Thauera)were the main factors for the changes in the abundance of sul2 genes.The function prediction of the microorganisms(Tax4Fun program)showed that the function of the microorganisms changed under the pressure of sulfamethoxazole,which promoted the expression of functional gene,inhibited the metabolism of microorganisms and the bacterial quorum sensing system,and improved the bacterial resistance.