Removal Mechanism And Efficiency Enhancement Of Benzo[a]Pyrene In Soil Microbial Electrochemical System

Soil microbial electrochemical system（SMES）,which integrates the electrochemical process with the microbial extracellular electron transport process,is a green,eco-friendly and potential in situ remediation technology for organic contaminated soil.Benzo[a]pyrene（BaP）,one of typical polycyclic aromatic hydrocarbons（PAHs）was chosen as the target organic contaminant.In this thesis,the degradation characteristics of BaP in SMES were studied,the influences of inorganic electron acceptors on the process acted by the bioanode in SMES was explored,a new adsorption permeable well-like SMES（APSMES）for enhancing mass transfer was constructed,and its performance in a short-term and a long-term opertation were investigated.This study can provide theoretical basis and technical guidance for practical application of SMES in remediation of PAHs contaminated soil.Degradation characteristics of organic matter and BaP in soil at 1 cm and 11 cm from the anode(S_{1 cm} and S_{11 cm})were compared.It was found that the bioanode accelerated the transformation rate of high-molecular-weight UVC humic acid-like substances to low-molecular-weight UVA humic acid-like substrances and fulvic acid-like substances.More fulvic acid-like in S_{1 cm} was detected after 100 days of operation.The degradation degree of BaP was improved by the bioanode,which resulted in more low-molecular-weight BaP metabolites in S_{1 cm} such as phenanthrene,methylphenanthrene,（2-naphthaloxy）-acetic acid and 1,3-dimethylnaphthalene.According to the microbial community structure and the corresponding metabolic pathways,the bioanode enriched electroactive microoganisms（EAM）and strengthened the contact between the EAM and BaP degraders,generating more adenosine triphosphatase,and thus altered the DOM transformation rate or the pathway,and enhanced the BaP degradation degree.The removal efficiency of dissolved organic carbon（DOC）and composition of residual dissolved organic matter（DOM）in soil,the BaP removal,the consumption of inorganic electron acceptors(dissolved Fe（III）and SO₄^2-)in SMES with or without addition of dissolved Fe（III）and SO₄^2-were all investigated.It was found that the growth of EAM could be inhibited and thus the startup rate of SMES was decreased when the dissolved Fe（III）and SO₄^2-were added in to soil.Addtion of dissolved Fe（III）and SO₄^2-did not affect the DOC’s removal efficiency and composition but significantly improved the degradation efficiency of BaP.The biodegradation efficiency of BaP in SMES were 9.33±3.33%and 27.58±1.87%after 50 days,respectively,without and with addition of dissolved Fe（III）and SO₄^2-in SMES.The EAM such as Anaeromyxobacteria and Desulfobacilium＿Catecholium could preference the bioanode as electron acceptors,which could generate more energy and thus improve the BaP biodegradation.An APSMES using water flow enhance the mass transfer of substrate in soil was constructed to enlarge the remediation range of SMES.The maximum power density generated by APSMES was approximately 30 m W/m².After 50 days of operation,the removal efficienfy of BaP amounts in soil was 52.52 4.23%.Among them,the anode adsorption and biodegradation accounted for 66.31±4.15%and 33.51±1.58%of the BaP removed from soil in APSMES,respectively.BaP can be transferred to,then adsorbed onto the bioanode and degraded via microbial electrochemical processes.The APSMES was operated for 240 days in the natural environment in Tianjin.After 240 days of operation,the microbial degradation efficiency of BaP in APSMES was 45.95%,which was 20%higher than that in APCSMES（38.17%）without water flow in soil.The water flow could transport BaP in the soil far away from the anode to the soil near the anode,simutaneously,and the water flow caused a complex and tight interaction between microbial species in soil S_{<1 cm},both of which improved the biodegradation efficiency of BaP in APSMES.In addition,it was found that the activity of EAM could be greatly reduced and thus cause a decrease in the output voltage of APSMESwhen the temperature is lower than 15℃.Therefore,the remediation period mainly from April to mid-November in Northern China（near the latitude of Tianjin）for the APSMES in practical application.