The Fate Of Antibiotic Resistance Genes In Membrane Bioreactors During Antibiotic Wastewater Treatment

Improper use of antibiotics has led to a serious environmental pollution problem.Residues of antibiotics have been found in natural water bodies or wastewater treatment systems in many countries.The migration,transformation,and synergistic effects of antibiotics and their metabolites with other xenobiotic pollutants in aquatic environments will lead to serious antibiotic resistance problems,posing a threat to human health and significant safety hazards to the ecological environment.Membrane bioreactor(MBR)are often used as an efficient wastewater treatment method for the removal of difficult to degrade organics such as antibiotics.The biodegradation of antibiotics in activated sludge is mainly divided into metabolism and co-metabolism,however,the relationship between microbial communities(such as heterotrophic and autotrophic bacteria)and antibiotic degradation and changes in resistance genes within the system during enhanced antibiotic removal by MBR remains unclear.In addition,non-antibiotic new contaminants promote non-specific enrichment of antibiotic resistance genes.Studies on the synergistic effects of co-exposure of new contaminants and antibiotics and their impact on resistance gene changes are lacking.Therefore,research in this area is important for controlling the development of resistance in the natural environment.Translated with www.DeepL.com/Translator(free version)This study selected the typical sulfonamide antibiotic sulfamethoxazole(SMX)for separate experiments on conventional pollutant removal and the fate of ARGs in MBR and studied the degradation pathway of SMX in MBR.Furthermore,common extraction agents,imidazolium-based ionic liquids(Cationic ILs),were selected for joint exposure with SMX in MBRs to explore the impact of compound pollutants on the removal of conventional and antibiotic pollutants,changes in sludge properties,and ARGs changes,aiming to further clarify the risks of resistance under compound pollution.The results showed that:(1)The membrane bioreactor(MBR)has the advantages of high sludge concentration and hydraulic retention time,which enables it to achieve thorough removal of different concentrations of SMX while effectively removing conventional pollutants such as COD and ammonia nitrogen,and maintain a high effluent quality.In the MBR,the metabolic activity of heterotrophic bacteria plays a major role in the biodegradation of SMX.SMX forces the enrichment of SMX-degrading bacteria in the MBR,while enhancing the formation of sludge flocs,providing a suitable living environment for functional microorganisms such as anaerobic denitrifying bacteria.With the acclimation of the microbial community in the MBR to SMX,the abundance of sulfonamide-degrading genes significantly increases,while the abundance of resistance genes decreases,which is related to the reduction of toxicity after SMX biodegradation.When the toxicity of SMX is strong before degradation,potential hosts of ARGs have a competitive advantage.After SMX is completely biodegraded and removed,the host bacteria of ARGs are gradually eliminated,and the abundance of ARGs decreases accordingly.(2)Under the joint exposure of Cationic ILs and SMX,the MBR exhibited good removal of conventional nutrients and antibiotic pollutants,indicating its stability in coping with complex pollution shocks.When the Cationic ILs concentration was increased to a certain level,the levels of reactive oxygen species(ROS)and lactate dehydrogenases(LDH)released from cell lysis were significantly increased.The amount of LDH stimulated by Cationic ILs was about 4-6 times higher than that of the group without Cationic ILs,indicating that the main toxic mechanisms of Cationic ILs include oxidative stress and cell membrane damage.Observation of sludge morphology showed that SMX promoted the formation of larger aggregate particles,while Cationic ILs forced loose and dispersed aggregate particles to disintegrate,retaining dense microbial aggregates and eventually forming a dense multi-layer structured sludge.When the Cationic ILs concentration was increased to a certain level,it significantly promoted the relative abundance and expression of ARGs,stimulated the overexpression of mobile genetic elements(MGEs),and thus increased the potential risk of ARGs transfer.Further analysis revealed that some potential ARGs hosts were positively correlated with more than four ARGs,belonging to multidrug-resistant bacteria.In summary,this study conducted basic research on the variation pattern of ARGs during the degradation process of antibiotics and complex pollutants in the MBR and investigated the changes in microbial community and sludge morphology of MBR in response to antibiotic resistance.It provides useful guidance for further controlling the risks of antibiotics and ARGs.