Mediating Mechanisms Of Dissolved Organic Matter On The Degradation Of 17?-ethynylestradiol By Electrochemical-Microbial Coupling Technology

17?-ethinylestradiol?EE2?,as main ingredients of contraceptives,belongs to environmental endocrine disruptors?EDCs?with high environmental risk and concern.It can produce a series of problems in growth,development and reproduction of living organisms even at concentration of 1 ng/L.EE2 enters the sewage treatment system with human or animal excreta,which is difficult to completely degrade or remove in conventional wastewater treatment processes.Microbial degradation is the main way for EE2 reduction during the environmental transformation.It still needs to be coupled with other technologies?such as electrochemistry?to improve the removal of EE2.Under the stimulation of micro-electric field,the changes of growth and reproduction of microorganisms,gene expression,and membrane permeability may be conducive to the removal of EE2.Previous studies have shown that dissolved organic matters?DOM?can be acted as an electron shuttle in a microbial system to accelerate the degradation of EE2 by coupling microorganisms.And this study further confirmed that DOM can also be stimulated in electrochemical systems to produce active substances to improve the degradation or mineralization efficiency of EE2.However,the degradation efficiency of EE2,the mediated role of DOM,the role of microorganisms treated by electrochemical-microbial coupling systems,and the effect of DOM on subsequent EE2 microbial degradation are still deserved to be explored.This study screened out the microbial strains that can effectively degrade EE2,and constructed the electrochemical-microbial degradation EE2 system in the presence of DOM with Ti/SnO₂-Sb₂O₅ as the anode and carbon material as the cathode.The interaction between electric field and microbial growth metabolism and community structure of microorganisms were studied.Furthermore,the mechanism of the effect of electro-excited DOM-generated active substances on EE2 degradation and the mechanism of DOM's coupling degradation in electrochemical-microbial system were investigated.Moreover,eco-toxicity for the EE2 degradation products was also evaluated.The feasibility of electrochemical coupling microbial technology to treat wastewater containing EE2 was verified.The main findings are as follows:?1?The effects of the oxidants?H₂O₂,potassium peroxodisulfate?PDS?,potassium peroxomonosulfate?PMS??and DOM on an electrochemical process for removing EE2 were investigated.The results showed that the oxidants significantly promoted EE2's degradation under acidic conditions.Meanwhile,the degradation efficiency of EE2 was increased with the addition of low concentration DOM in electrochemical system under acidic conditions due to the increasing of hydroxyl radical's concentration.However,the EE2 degradation rate was reduced obviously as the concentration of DOM increased.?2?An electrochemical-microbial coupled degradation system was constructed to remove EE2.It was found that EE2 removal was promoted at high dissolved oxygen concentrations and low pH in electrochemical process.Coupling electrochemical with anaerobic bacteria system could improve the EE2 removal with a reaction rate constant of 0.0195 min^-1 in 100 mA and pH5.5 due to high·OH production and malondialdehyde?MDA?concentration.An electric current inhibited the growth of most microbial species,but Shewanella and Aeromonas survived well in anaerobic condition.Electroactive microorganism can enhance the efficiency of direct electron transfer between the bacteria and the electrodes,resulting in the promotion of EE2 degradation.The results also showed that electrochemical microorganism coupling method was more energy saving.?3?DOMs mediated in the degradation of EE2 in a coupled electrochemical and biological system.Fulvic acid?FA?and Sigma humic acid?SHA?could promote EE2 degradation with the addition of domesticated micro-organisms in the coupled system.Analyses of superoxide dismutase levels?SOD?,electron transfer capacity?ETC?and electrochemical impedance spectroscopy?EIS?confirmed the promotion of electron transfer capacity and bioavailability of DOM after treated by the coupled system.Stimulated micro-organisms seemed to increase their environmental tolerance and degrade EE2 more effectively.The EE2 degradation products in the coupled system were investigated as follows:EE2 was oxidized and transformed into E2,E1 or other hydroxylated products by hydroxyl radical or microbial oxidase;and then the ring structures were opened in the same oxidation way;next,the ring opening products were oxidized to an organic carboxylic acid,which was mineralized by the system finally.?4?This paper further explored the mechanism of DOM medited in electrochemical and microbial coupling system,and the effect of effluent from coupling system on the migration and transformation of pollutants in the natural environment.The results illustrated that the efficiency of EE2 biodegradation was shown to be strongly correlated with electron accepting capacity?EAC?of DOM.After electro-modification,the amount of quinone-type structures in DOM increased,resulting in the high triplet-state DOM moieties contribution in the EE2photolysis process,and it had a high EE2 photochemical and microbial degradation efficiency with the addition of electro-modified DOM.The cellular polymeric substances?CPS?secreted by microorganisms contained photosensitive substances?mainly proteins or amino acids?could be excited and transformed into the triplet states to promote EE2 degradation.Less toxic EE2 degradation products after treated by photolysis combined with biodegradation were evaluated.This study explored the role of DOM in the coupled electrochemical and biological system,and provided new ideas for the treatment of estrogen-contaminated waters.It was confirmed that the electrochemical coupling microbial technology can be employed on estrogen-contaminated wastewater treatment.And it presented a a theoretical basis for the application of electrochemical-microbial technology to remove steroids from wastewater.The study also demonstrated the DOM treated by electrochemical system has a positive effect on the natural degradation of organic pollutants.