Promoting Effect Of Soil Bioelectrochemical System Optimization On Heavy Metal Removal

Heavy metals have become difficult and hot spots in the field of soil remediation,because of its persistence,potential toxicity and non-biodegradability.In recent years,the microbial fuel cell（MFC）technology has been equipped with 1)directly recover chemical energy from sewage and output it in the form of electrical energy;2)the internal electric field formed can directionally drive the migration of heavy metals;3)the reducing performance of the cathode can reduce oxidizing substances,such as:oxygen,Cu²⁺and other characteristics have been widely concerned.In this study,two types of soil MFC（three-chamber soil MFC and two-chamber soil MFC）were constructed to repair heavy metal contaminated soil.This paper studies the influence of types of assistants and soil types,composite heavy metal and MFC electrode configuration on the electric power generation performance of soil MFC,the migration and removal efficiency of heavy metal and the response relationship between the two,and analyzes the removal mechanism and influence mechanism of heavy metal in soil MFC.The specific research content and results are as follows:The effects of the types of desorption agents on the MFC electricity generation performance and heavy metal removal in the three-chamber soil were studied.1mol/L hydrochloric acid（HCl）、citric acid（CA）and acetic acid（HAC）were selected as additives to the soil MFC.The results show that the removal rate of heavy metals in the MFC is 28.21%（CA）,40.03%（HCl）and 8.45%（HAC）,MFC with HCl has the strongest promoting effect on the migration and removal of heavy metals.Although CA significantly enhances the copper migration ability,the stronger internal electric field obtained by adding HCl is the fundamental driving force to promote copper migration and removal.At the same time,the acidification of HCl removes 4.32%of the reducible state and 28.60%of the oxidizable heavy metals,which further promotes the removal of Cu.The effects of soil type on the electricity generation performance,morphological distribution of heavy metals and removal efficiency of MFC in three-chamber soil were studied.Two typical soils with significant differences in physicochemical properties of loess and laterite were selected as the research objects.The results show that compared with laterite,loess has higher physical and chemical properties such as p H,cation exchange capacity and organic matter,resulting in 6.84 and 2.68 times the content of oxidizable and reducible heavy metals than laterite,and the content of acid-extractable heavy metals that are easily migrated only reaches 45.20%of laterite.The removal rate of Cu with MFC added red clay can be as high as 36.42%.However,due to the high porosity of the laterite,the larger pore size of laterite and the weaker electric field strength of the laterite-MFC,the removal of copper in the laterite is mainly dependent on diffusion,while the removal rate of Cu under electromigration is only 14.49%.The heavy metals in loess are mainly removed by electromigration（21.47%）,and the removal amount is 1.48 times that of laterite,which is more suitable for repair under MFC micro-electric field.The effect of compound heavy metal pollution on the MFC electricity generation performance and migration and removal of heavy metals in three-chamber soil was studied,and the interaction between heavy metals was analyzed.Choosing Cu and Pb as contaminated heavy metals,the results show that the maximum power density of MFC in Cu&Pb contaminated soil is 102.76 m W/m²,which is higher than that of single Pb contaminated soil MFC（80.50 m W/m²）and less than single Cu contaminated soil（125.78 m W/m²）..Due to the presence of Pb,the MFC production capacity of Cu&Pb contaminated soil was reduced from 354.07 m W·h（single Cu contaminated soil）to 334.39m W·h,and the antagonism between heavy metals inhibites the desorption of Pb by CA,making the acid extractable Pb content decreases from 52.72%（single Pb contaminated soil）to 42.31%（Cu&Pb contaminated soil）,resulting in a significant reduction in the removal rate of Cu and Pb in Cu&Pb contaminated soil MFC than single contaminated heavy metal,from 44.61%to 34.25respectively%（Cu）,from 11.65%to 4.54%（Pb）.The effect of electrode configuration on the power generation performance and heavy metal removal of dual-chamber soil MFC was studied.The single anode and single cathode MFC,double anode and single cathode MFC and single anode and double cathode MFC were constructed under the condition that the total area of cathode and anode was fixed.The results show that:under the limitation of cathode performance,the double anode/cathode MFC cannot improve MFC Power generation performance.Although the dual anode/cathode MFC configuration increases the electron transfer channel and reduces the internal charge transfer resistance of the anode,the anode internal resistance is reduced from 287.65Ω（single anode single cathode）to 145.96Ω（double anode single cathode）and 165.38Ω（Single anode double cathode）,MFC power generation increased from 1670.57C（single anode single cathode）to 1938.07 C（double anode single cathode）and 2041.5 C（single anode double cathode）.However,due to the slow reaction rate of the cathode,the electrons transferred to the cathode accumulate on the surface of the cathode sheet,which increases the activation loss of the cathode.As a result,the internal resistance of the dual anode/dual cathode configuration is16.04～17.96 times that of the single anode and aingle cathode configuration.Based on the better power generation performance and higher internal electric field strength of the single anode single cathode MFC,it obtains the highest heavy metal removal efficiency.