Effect Mechanism Of Antibiotic Florfenicol On Enhanced Biological Phosphorus Removal Process

Florfenicol（FF）,a derivative of chloramphenicol,is widely used in livestock and aquaculture because of its broad antimicrobial spectrum,rapid absorption,long half-life and non-anaplasmogenic properties.Recently,studies have reported the detection of FF in the influent and effluent of wastewater treatment plants.Enhanced biological phosphorus removal（EBPR）is now widely used in wastewater treatment plants to improve phosphate removal and address eutrophication in water bodies because of its economy,simplicity and sustainability.the operation of EBPR systems involves the participation of various microorganisms and is susceptible to external factors.However,the potential impact of FF on the EBPR system has not yet been reported.In this study,EBPR systems were constructed to investigate the effects of different concentrations of FF short/long term exposure on nutrient removal rate and nutrient changes in EBPR system in typical cycles,the impact of FF on microbial community of EBPR system after long-term exposure and the interaction between FF and EPS in activated sludge after long-term exposure to reveal the potential mechanism of FF effects.Firstly,This work investigated the effect of short-term FF exposure on the performance of EBPR,and the result showed that the exposure concentrations of FF at below 0.1 mg/L did not affect the performance of EBPR,while at concentrations up to0.5 mg/L and 2.00 mg/L,the soluble orthophosphate（SOP）removal rate decreased to91.17±1.71%and 85.53±1.71%,respectively,indicating that the higher concentrations of FF short-term exposure inhibited the biological phosphorus removal of EBPR.Additionally,the effect of FF on EBPR was dose-dependent.The analysis of selected typical cycle showed that short-term exposure to higher concentrations of FF inhibited the anaerobic phosphorus release and aerobic phosphorus uptake in the biological phosphorus removal process.During the FF long-term exposure experiment,the effect of higher concentration of FF on SOP removal rate in EBPR can be divided into two phases,i.e.,inhibition period and recovery period,althoμgh there was a recovery period,there was still inhibition relative to the control and low concentration experimental groups,and the analysis of selected typical cycles showed that the inhibition is mainly reflected in the aerobic phase.Long-term exposure to higher concentrations of FF led to a slight increase in effluent COD.Neither short-term nor long-term FF exposure had any effect on the biotransformation of NH₄⁺-N in EBPR.Afterwards,this work analyzed the effect of long-term FF exposure on microbial community structure using high-throμghput sequencing,and the results showed that0.01 mg/L FF increased the diversity and richness of microbial communities,while 2.00mg/L FF decreased the diversity and richness of microbial communities.In addition,the variability of microbial communities became more and more obvious with the increase of FF exposure concentration.2.00 mg/L FF increased the relative abundance of Candidatus Competibacter,Tetrasphaera,and Terrimonas to 19.00%,5.28%,and 16.28%,respectively,but significantly decreased the relative abundance of Chinophagaceae,which may be one of the reasons why the efficiency of biological phosphorus removal recovered in 2.00 mg/L FF experimental group but there was still inhibition.Based on the above works,this work simultaneously investigated the effects of long-term FF exposure on activated sludge characteristics.The main purpose was to clarify the effect of FF on activated sludge by examining its interaction with extracellular polymer substance（EPS）in activated sludge.The results showed that protein,polysaccharide and PN/PS in EPS would show a trend of decreasing and then increasing with the increase of FF concentration.Throμgh three-dimensional excitation-emission matrix（3D-EEM）analysis,it was found that 2.00 mg/L of FF led to changes in protein conformation and fulvic acid structure in EPS and resulted in an increase in functional groups such as hydroxyl,carboxyl and amino groups,which may potentially enhance the adsorption of FF.X-ray photoelectron spectroscopy（XPS）analysis showed that the relative proportions of C-（C-H）single-chain forms in lipid or amino acid side chains and C=O in carboxylic acids,carboxylates,carboxylates or amides decreased with increasing FF concentrations,but the relative proportion of C-F₃ signals was much higher at higher FF concentrations（4.40%）than in other environments（<1.7%）.The above results sμggested that EPS in sludge may have adsorption for FF to some extent.The interaction between EPS and FF resulted in a change in the electron distribution in EPS and an increase in the electron density around the carbon atom in C-（O,N）.This work investigatedthe effect of FF on EBPR and analyzed its mechanism,which provided the necessary theoretical basis and technical reference for strengthening the ecotoxicity control of FF within wastewater treatment.