Role Of Dissolved Organic Matter From Natural Biofilm In Oxytetracycline Photodegradation In Waters

The antibiotics widely detected in natural waters are a new type of environmental pollutants,and their environmental characteristics in natural waters have attracted the attention of researchers in recent years.Photochemical degradation is one of the major degradation pathways of antibiotics in water environment,which significantly affects its migration,transformation and fate in the water environment.Dissolved organic matter（DOM）with light absorbing properties is the main light absorbing material in surface water and it is one of the important factors that affect the photodegradation of organic pollutants in water environment.With regard to humic DOM,such as fulvic acid,the effects of photodegradation of antibiotics have been well studied.Algae-based natural water biofilms will continue to secrete DOM into the water during its new generation.This kind of non-humification DOM produced by metabolism and its effects on the photodegradation of antibiotics has rarely been reported.The research on the effect of biofilm-produced DOM（BDOM）on the photodegradation of antibiotics will help to reveal the effect of biofilm on the antibiotic’s water environment behavior and the migration and transformation of antibiotics in water environment.In this paper,the effect of BDOM on the photodegradation of OTC was studied using tetracycline antibiotic oxytetracycline（OTC）with high detection and detection in natural water as the target compound.First of all,by extracting BDOM and comparing it with humification DOM（Furonic acid,FA）,UV-Vis spectroscopy,three-dimensional fluorescence spectroscopy and infrared spectroscopy were used to analyze the difference of the two spectral characteristics.Secondly,the initial photodegradation characteristics of OTC in this study were determined by the initial experimental conditions,and then the effects of two DOMs on the photodegradation kinetics of OTC were studied,and the reactive oxygen species（ROS）in the system under the presence of two DOMs were quenched further analyzed the mechanism of the effects of BDOM and FA on photodegradation of OTC.Finally,through the study of the water-biofilm system,the effect of biofilm on photodegradation of OTC was initially determined.The results of the study showed that by extracting BDOM and comparing it with FA,BDOM has smaller molecular weight,lower aromaticity,lower hydrophobic component,and weaker light absorption ability in the UV region than the two DOMs.FA has more aromatic ring structure than BDOM;both contain a large amount of fulvic acid-like,protein-like,but the content of fulvic acid is lower in BDOM.The photodegradation rate of OTC decreased with the increase of concentration,and the photodegradation rate gradually decreased from 12.44×10^-22 min-1 to 6.07×10^-22 min^-1.The photocatalytic degradation of OTC was opposite for the two DOMs.BDOM vs.OTC Photodegradation played a promoting role.With the increasing of BDOM concentration,the photodegradation rate of OTC increased from 9.7×10^-22 min^-11 to19.9×10^-22 min^-1.FA inhibited the photodegradation of OTC.With the increasing of FA concentration,the photodegradation rate of OTC decreased from 8.9×10^-22 min^-11 to5.6×10^-22 min^-1.The effect of both DOMs on the photodegradation of OTC decreased at high concentrations.By quenching ROS in both systems,in the presence of BDOM,the excited triplet DOM（³DOM*）simultaneously promotes the degradation of H2OTC and HOTC^-.However,there was no significant difference in ROS quenching experiments in the presence of FA.FA inhibits OTC photodegradation by the strong light shielding effect,while BDOM promotes OTC photodegradation by forming³BDOM*.In the water-biofilm system,the photodegradation rate of OTC increased from 9.15×10^-22 min^-11 to 13.10×10^-22 min^-11 with the increase of biofilm amount,and the existence of biofilm promoted the OTC.Photodegradation in water.