Removal Efficiency And Mechanism Of Ofloxacin In Rural Wastewater Treatment Facility Based On ABR-hybrid Constructed Wetland

With the development of rural economy and improvement of living standards,pharmaceuticals and personal care products（PPCPs）are used increasingly and frequently.The common PPCPs include antibiotics,non-steroidal anti-inflammatory and some personal care products.Due to the abuse of antibiotics,different concentrations of antibiotics have been detected in rural sewage.Most rural areas lack completed sewage collection pipes and sewage treatment facilities becaused it is limited by economic and geographical restrictions in rural areas,which leading to antibiotics entering into environment through various ways.Then,it may cause some environmental risks to the rural ecological environment.In this study,four rural sewage treatment facilities in Guizhou province were selected to carry out antibiotic pollution level and ecological risk analysis.Based on this,a rural sewage treatment facilities based on anaerobic baffle reactor（ABR）-hybrid constructed wetland was used to explore the removal efficiency and mechanism of the targeted antibiotic of ofloxacin.Fourier transform infrared spectrometer（FTIR）and three-dimensional fluorescence spectroscopy（3D-EEMs）were used to analyze the change characteristics of the components in effluent.16S r RNA sequencing analysis and metagenomics were used to elucidate the removal mechanism of pollutants in system.The results as follows:（1）Different antibiotics in the influent and effluent of Guizhou rural treatment facilities were detected.Sulfamethoxazole（SMX）,oxytetracycline（OTC）,chlortetracycline（CTC）,tetracycline（TC）and ofloxacin（OFL）were the main antibiotics,which the concentration ranged from ND to 417.57 ng·L^-1.The removal rate of antibiotics in the four rural wastewater treatment facilities ranged from-58.32%to 61.07%.OFL was the major high-risk pollutants in effluent,posing an ecological risk to the environment.（2）ABR-hybrid constructed wetland could realize the high removal efficiency of conventional pollutants and OFL simultaneously.This system had a high removal efficiency of pollutants under different volume loads（0.034,0.085 and 0.119kg COD/（m³·d））.Pollutants could be obtained the best removal efficiency at volume loads 0.085 kg COD/（m³·d）,the average removal rates of nitrogen and phosphorus pollutant（29）94%,COD（29）82%,OFL（29）90%.The adsorption of biofilm and plants was the major removal ways of OFL,and the OFL adsorption of biofilm was higher than plant.The removal rate of conventional pollutants decreased obviously after adding OFL,and the performance of system was inhibited.（3）FTIR analysis and 3D-EEMs spectroscopy analysis were used to analysis the composition characteristics of substances in influent and effluent of the system.FTIR analysis demonstrated that the peak caused by the nitrogen and phosphorus pollutants disappears obviously and the peak intensity weakens significantly after the system treating.OFL was degraded and its structural stability was damaged to a certain extent in the system.3D-EEMs spectroscopy analysis showed that the system could realize a high removal efficiency of tyrosine and tryptophan protein,humic acid-like substances,fulvic acid-like substances and soluble microbial metabolites,and these substances disappeared in the effluent before OFL adding.After OFL was added,the removal ability of humic acid-like substances,fulvic acid-like substances and soluble microbial metabolites was decreased of system.The effluent still contained a certain amount of fuli acid and humic acid.（4）16S r RNA gene sequencing showed that microbial community structure was changed after OFL was added.There are a number of bacterial related to carban and nitrogen metabolism,such as Chlorobium,norank＿c＿＿Bacteroidetes＿vadin HA17,Thiothrix,Hyphomicrobium and Nitrospira.Also methanogens including Methanosarcina,Methanosaeta,Methanobrevibacter and Methanobacterium exist in this system.Microbial diversity and abundance were decreased after the addition of OFL in A reactor,among which the abundance of Bacteroidetes and Proteobacteria decreased,but the abundance of Firmicutes and Actinobacteria increased.The addition of OFL makes the dominant archaea more obviously,and the abundance of Crenarchaeota in HF is as high as 95%.There are Bacilli,Clostridia,Trichococcus,Thiothrix and Syntrophorhabdus which related to OFL microbial degradation in this system.（5）Microbial structures,functions and metabolic pathways were analyzed based on metagenomics.The dominant genus is unclassified＿d＿＿Bacteria,Methanosaeta,Nitrospira,Thiothrix,Clostridium,Lachnocostridium and Thiocapsa in B reactor.Metabolism was the main function in system by functional annotations,and there was xenobiotics biodegradation and metabolism.Methanosaeta and Nitrospira were the major bacterial of metabolism and genetic information processing.Nitrospira,Clostridium and Lachnocostridium were the key species of environmental information processing and cellular processes.Mexd,mexf and mexb affiliated with quinolone antibiotic resistance genes and nor B,nir B,nir K,nrf A and amo ABC gene related with nitrogen transformation function genes were also found in this system,and there is completed nitrogen metabolism.Network analysis revealed that unclassified＿d＿＿Bacteria,Methanosaeta and Nitrospira were the key microorganisms in the system.What’s more,there was a significant positive correlation between Thiothrix,Pseudomonas and unclassified＿d＿unclassified.