Effect And Mechanism Of Enhanced Removal Of Typical Aquaculture Pollutants By Bioelectrochemical Floating Bed System

Aquaculture plays an important role in China’s fishery development.However,with its development,the aquaculture pollution has been complex and serious.Different kinds of pollutants can accumulate in the water and sediment,leading to new environmental risks.Bioelectrochemistry system（BES）,a technology based on the coupling of microbial and electrochemical treatment,which inherits the advantages of microbial treatment,including high efficiency,low cost and low environmental risks.Moreover,BES could make full use of in-situ electricity generation to enhance the bioelectrochemical purification,which has drawn great attention all over the world.This study takes advantage of the anaerobic/aerobic characteristics of aquaculture environment to construct a bioelectrochemical floating bed system（BEFS）.In addition,this study focuses on the simultaneous treatment of refractory organic matter in sediment and typical pollutants in water as well as exploring the mechanism within this process to provide theoretical support for realizing the potential of BEFS.In this study,polycyclic aromatic hydrocarbons（PAHs）in sediments and nitrate and antibiotics in water were taken as target pollutants.This study focused on the following aspects:（1）effects and mechanism in removing PAHs in sediments using BESF;（2）application of the electron shuttle（ES）to accelerate electron transport for improving PAHs degradation;（3）denitrification effect and mechanism in aquaculture water by BESF cathode;（4）removal performance of nitrogen and antibiotics in aquaculture water by using modified cathode;（5）Effect of cathode-anode coupling on simultaneous removal of pollutants from sediment and water.The specific conclusions were as follows:（1）BESF was constructed in aquaculture sediment for electricity generation and has significantly improved the PAHs removal up to 1.40,1.57 and 1.50 times for naphthalene（Nap）,phenanthrene（Phe）and pyrene（Pyr）,respectively.The anode potential and current were the key factors affecting PAHs removal,which were positively correlated with the removal efficiencies of all three types of PAHs.In the degradation process of PAHs,the BEFS anode served as a sustainable electron acceptor to accelerate PAHs degradation.In addition,the electric current of BESF can increase the contact probability of electrons and PAHs（and their degradation products）,which can promote the progress of reductive degradation steps,and finally improve PAHs removal.（2）The ubiquinone（Co Q）and humic acids（HAs）,as electron shuttle（ES）,mainly relied on the mediation of quinone groups to create electron transport network in sediment,providing long-distance extracellular electron transport pathway to facilitate PAHs degradation,especially for PAHs away from anode.HAs contains complex non-quinone groups,which also mediated electron transfer.Furthermore,the transformation of its components under electrochemical influence also was beneficial for PAHs degradation.（3）BEFS cathode served as electron donor by using electrons generated by anode to promote nitrate reduction in low C/N aquaculture water.By activating nitrate reductase and providing electron required for reduction,bioelectrochemical effect enhanced denitrification activity of cathodic microbes,increasing TN removal efficiency by about 50%.（4）The conductive polymer（PEDOT）and metal oxide（Mn O₂）were attached to the cathodes,respectively.The modified cathodes improved the electron transfer ability of the material interface by introducing redox groups and metal ion pairs,showing greater electrochemical activity as well as higher pollutant reduction removal and achieving a 40%to 60%increase in the output current.The two modified cathodes improved nitrate reduction under antibiotic water by 20%.In addition,by accelerating reductive degradation,they also improved sulfamethoxazole removal by 30%.（5）With BEFS cathode and anode coupling for synchronous treating,the removal characteristics and influencing factors of pollutants in water and sediment were studied.It was found that BEFS could obtain about 0.5 m A output current and enhanced the removal efficiencies of Nap,Phe,Pyr in sediment to 59.1%,39.6%,and 34.1%,respectively.At the same time,BEFS also led to an increase of about 80%and 50%in terms of removal efficiencies of TN and SMX in water.These results could provide theoretical support for in-situ utilization of electricity generated by BEFS as well as exploring new methods to synchronously promote the oxidative and reductive degradation of pollutants in sediment and water.