Research On Heavy Metal Migration And Cathodic Reduction Characteristics In MFC

Due to its non-biodegradability,poor migration capacity,long persistence period and high ecological toxicity,heavy metals in soil have become the research difficulties and hot spots in the field of soil pollution remediation.Compared with traditional treatment methods,the microbial fuel cell?MFC?has attracted more and more attention because of its good pollutant removal ability and electricity generation performance.In this study,a three-compartment microbial fuel cell was constructed to remediate heavy metal contaminated soil by using the electricity generated by MFCs.Cu was selected as representative heavy metal,and Cu contaminated soil was treated by sequential batch treatment.The effects of electrode spacing,external resistance,desorption agent and initial Cu concentration on the electricity generation performance and heavy metal migration and cathodic reduction of three-compartment MFC were studied respectively.The main research contents and results of the study were as follows:?1?The effects of electrode spacing and external resistance on the electricity generation performance of MFCs and the migration and reduction of heavy metals in three-chamber MFC were investigated.It was found that the removal and reduction of Cu could achieve in the three-compartment MFC,and the acetic acide xtracted and reducible forms of heavy metal were the most easily migrated forms.The MFCs with electrode spacing of 5 cm,10 cm,15 cm,and 20 cm were set as the research objects.The smaller electrode spacing is beneficial to the migration of total Cu in the soil and the reduction of Cu²⁺in the cathode chamber.The removal rates of acetic acid extracted Cu and reducible Cu in MFC-5 cm near-anode soil were1.56 and 1.81 times higher than those of MFC-20 cm,respectively.It was also found that the increase of internal resistance was the main reason for the significant decrease of the output voltage and the maximum power density of MFCs with larger electrode spacing?>10cm?.Compared with MFC-10 cm,the internal resistance of MFC-20 cm increased by 84.70%,while the maximum power density decreased by 56.36%.The MFCs with external resistance of 100?,510?,and 1000?were set as the research objects.With the increase of external resistance,the output voltage increased,and the removal rates of acetic acid extracted Cu and reducible Cu in near-anode soil were higher.The removal rates of acetic acid extracted Cu and reducible Cu in MFC-1000?near-anode soil were 59.02%and 46.33%,respectively.In addition,Cu²⁺was reduced to metal Cu in the cathode chamber of MFC-1000?.?2?Citric acid was used as assisting agent,MFCs with agent concentration of 0.2 mol/L,0.5 mol/L and 1 mol/L were set as the research objects,and closed-circuit MFC with pure water added to the soil was set as the control group.It was found that adding assisting agent to the soil can increase the proton transfer rate,reduce the internal resistance of MFC,thus enhance the electricity production performance of MFC.When the concentration of assisting agent increased from 0 to 1 mol/L,the internal resistance decreased by 28.13%and the maximum power density increased from 0.75 W/m³ to 0.99 W/m³.The higher the concentration of assisting agent,the higher the ratio of acetic acid extracted Cu in initial soil,which was favorable to the migration and removal of Cu in the soil.When the concentration of assisting agent was 1 mol/L,the acetic acid extracted Cu removal rate in the near-anode soil and the total Cu removal rate in the whole soil chamber were 70.40%and 37.03%respectively.In addition,the concentration of the assisting agent did not affect the composition of the cathode reduction product?both metal Cu?.?3?MFCs with initial Cu concentration of 100 mg/kg,300 mg/kg and 500 mg/kg were set as the research objects.It was found that increasing the initial Cu concentration in the soil can improve the electricity production performance of MFC by improving cathode potential and reducing internal resistance of the device.When the initial Cu concentration increased from 100 mg/kg to 500 mg/kg,the maximum power density increased from 0.26 W/m³ to0.72 W/m³,the total Cu removal in the whole soil chamber increased significantly from 12.13mg to 54.55 mg,a 3.5-fold increase.The new three-chamber MFC is more suitable for the remediation of high-concentration heavy metal contaminated soil.