The Co-effects Of Carbon Nanotubes And Ampicillin On Performance,Population Structure And Resistance Genes Of The Activated Sludge

As a growing number of antibiotics are detected in wastewater and natural water bodies,the antibiotic residues have become a serious environmental issue because they could result in the development of antibiotics resistant bacteria(ARB)and antibiotics resistance genes(ARGs).Because most of the wastewater treatment plants(WWTPs)mainly use activated sludge to reduce pollutants,many kinds of resistant microorganisms and resistant genes have been detected in the effluent of WWTPs.Serving as a shield of public health,WWTPs receives various contaminations including emerging contaminants,such as synthesized nanoparticles(NPs).NPs have a certain physiological toxic effect on the activated sludge in WWTPs,and then bring a certain ecological risk to the environment.Although there’s a good chance that both NPs and antibiotics are present in WWTPs,their co-effect on the physiological state of microorganisms and resistance genes in activated sludge is not yet clear.In this study,the response of activated sludge exposed to multi-walled carbon nanotubes(MWCNTs)and ampicillin(AMP)was investigated in a sequencing batch reactor(SBR),including the influences on the operating state of SBR,the physiological state of microorganisms and microbial community structure and abundance changes of ARGs.In this study,by studying the interaction between MWCNTs and AMP,the response mechanism of activated sludge in SBR under the co-existence of NPs and antibiotics was preliminarily discussed.Based on the above research purposes,the main research contents and results of this paper are as follows:1.The effects of the co-existence of MWCNTs and AMP on the performance of activated sludge were investigated by monitoring the operational indexes of SBR,such as the concentration of mixed liquor volatile suspended solids(MLVSS)and specific aerobic rate(SOUR).The treatment effects of MWCNTs and AMP on simulated water samples in SBR were discussed by monitoring the concentration of total organic carbon(TOC)and AMP in the effluent.The results showed that mixed liquor volatile suspended solid(MLVSS)values exposed to MWCNTs and AMP decreased to 83.48-90.53%,but the specific oxygen utilization rate(SOUR)was even higher with respect to the control for 24 h exposure.Meanwhile,the TOC values of the effluent fluctuated from between 3.3 and 3.7 mg/L during the whole exposure experiment,in which the AMP concentrations showed a decreasing trend and then an upward trend with the operation time.2.Flow cytometry,fluorescence microscopy and other analytical instruments were used to analyze the physiological states of microorganisms in activated sludge,such as membrane permeability,living/dead cell ratio,cell death modes,cell metabolism and proliferation activity.The effects of the co-existence of MWCNTs and AMP on the physiological activity of microbial cells were studied.The toxicity of the co-existence of MWCNTs and AMP on cells was studied by measuring the EPS components of microorganisms in activated sludge and intracellular ROS content.The results showed that compared to individual AMP,the co-occurrences of AMP and MWCNTs showed lower cytotoxicity to activated sludge,supported by a lower membrane permeability(66%-81%of the control sample)and higher cell metabolic viability(1.19-3.91-fold of the control sample).In addition,studies showed that the cellular ROS level was about 1.5-2-fold that of control sample as AMP and MWCNTs co-existed in the SBR.3.Microbial community structure and the change of abundance of ARGs(blaFOX,blaDHA,Lak,16S-rRNA,intI,intI2)in activated sludge were investigated by high-throughput test and fluorescence quantitative PCR.The results showed that the microbial community structure changed when exposed to AMP and MWCNTs.Firmicutes phylum emerged in the top 20 phyla under the co-effect of AMP and MWCNTs,but not for other reactors.It is worth noting that the relative abundances of antibiotic resistance genes(ARGs)under the co-effect of AMP and MWCNTs were significantly increased,especially blaDHA.A high relative abundance of intll and intI2,which are considered as potential indicators for ARGs horizontal transfer in double pressure meant that the MWCNTs showed a synergistic effect on ARGs horizontal transfer when they were combined with antibiotics.This study has been clear about the co-effects of MWCNTs and AMP on activated sludge microbial physiological states and abundance of the resistance gene,to a certain extent,it also reveals the response mechanism of multiple pollutants exposure.This study has some implications for understanding how NPs affect the distribution and transmission of ARGs in complex environment.