Research On The Synthetic Effect Of Antibiotics And Cu NPs On Anammox System

Antibiotics widely exist in the livestock wastewater.High concentration antibiotics in wastewater usually have a strong biological toxicity.The occurrence and spread of antibiotic resistant genes（ARGs）antibiotic resistant bacteria（ARB）stimulated by antibiotics have been listed as emerging pollutants.Furthermore,the majority of livestock wastewater contains high concentrations of ammonia nitrogen and heavy metals.Improper management will pose a significant risk to the environment and even human health.However,the traditional biological treatment process is difficult to remove high concentration of nitrogen under the stress of heavy metals and antibiotics.Anaerobic ammonia oxidation（anammox）process,as a new biological nitrogen removal process with high efficiency and low consumption,has attracted much attention in the sewage treatment industry.However,anammox process is easily disturbed by environmental pollutants such as antibiotics and heavy metals.At present,the successive effects of antibiotics and heavy metals on anammox process remain unknown.There are a wide range of sewage sources and various types of pollutants in the actual sewage treatment plant.The followings were the main findings of this study:（1）Gradually increasing antibiotic concentrations can effectively domesticate the microbial community of anammox system,which could realize the stable operation of anammox process under spiramycin（SPM）and streptomycin（STM）stress.In terms of nitrogen removal performance,0.5 mg L^-1 SPM and 5 mg L^-1 STM could be considered as the threshold concentrations of both antibiotics in anammox process under long-term stresss.Although high concentrations of SPM and STM had an inhibitory effect on anammox process,this inhibitory impact was recoverable,and the recovery period was shortened as the antibiotic concentrations increased.The final treatable concentrations of SPM and STM are 5.0 mg L^-1 and 50 mg L^-1,respectively.This domestication strategy was beneficial to anammox process,which could treat wastewater containing SPM and STM.Meanwhile,the increasing Protein/Polysaccharide（PN/PS）indicated that the sludge stability of anammox granule was also improved.This domestication strategy was also beneficial to the optimization of microbial community structure in anammox system.As the main anaerobic ammonia oxidation bacteria（An AOB）in the system,the relative abundance of Candidatus Kuenenia remained generally stable during the operational period,verifying the superiority of this domestication method.This section of this study illustrated the feasibility of anammox process in the treatment of antibiotic containing wastewater from the aspects of nitrogen removal performance,characterization of sludge properties and microbial community structure.（2）The antibiotics pre-exposed anammox granules were more sensitive to copper nanoparticles（Cu NPs）.The inhibitory impact of 5 mg L^-1 Cu NPs on antibiotics pre-exposed anammox granules was more significant than that of the normal anammox granules,and the reactor degradation time was 5 days earlier than that of the normal anammox granules.After the addition of Cu NPs for 25 days,the concentrations of NH₄⁺-N and NO₂^--N in the effluent of the reactor where the antibiotics pre-exposed anammox granules were cultivated were as high as 148.6 mg L^-1 and 117.5 mg L^-1,respectively.Nevertheless,after stopping adding Cu NPs,the nitrogen removal performance of the system could be restored in two generations.At the micro level,the addition of Cu NPs led to the microbial community richness of the two anammox sludge was significantly lower than the initial level,but after the addition of Cu NPs was stopped,the microbial community diversity and richness of these two kinds of anammox sludge recovered to the initial level.The different responses of the two sludges to the Cu NPs stress showed that the selection of seed sludge was very important for the stability of anammox process operation,which could provide theoretical guidance for the operation of actual sewage treatment plant using anammox process.（3）Cu NPs drived the Interspecific horizontal transfer of ARGs and cop A between microorganisms mediated by int I1 through the co-selection mechanism.Stimulated by Cu NPs,the abundance of STM resistance genes（aac6ib,aph6id,aad A and aad B）and SPM resistance genes（ere A,erm B,erm F and erm Q）in both normal anammox sludge and antibiotics pre-exposed anammox sludge increased by 1-2 orders of magnitude,especially in antibiotic antibiotics pre-exposed anammox sludge.In addition,the abundance of copper resistance gene（cop A）and int I1 also increased significantly.Network analysis showed that ARGs and cop A were significantly correlated with int I1,indicating that the transmission of ARGs and cop A in anammox system was mainly mediated by int I1,and its potential carrier bacteria was Subgroup＿10.