Study On Purification Characteristics Of Organic-heavy Metal Compound Pollution In Soil By Bioelectrochemical System

Organic-heavy metal compound pollution is one of the most common types of soil pollution.The interaction between pollutants and different removal mechanisms increase the difficulty of soil remediation.Microbial fuel cell（MFC）has received widespread attention because it has the ability to efficiently remove heavy metals and refractory organics in the soil,and is cleaner and more economical than traditional remediation technologies.In this study,a dual-chamber soil MFC was constructed to remediate soil contaminated by organic-heavy metals.This paper starts from three aspects of soil MFC power generation performance,pollutant removal efficiency and electron transfer efficiency,which mainly focuses on the pollutant removal characteristics of soil MFC under compound pollution conditions,the synergistic regulation effect of soil MFC on the removal of organic-heavy metal compound pollution,and the promotion of electricity generation and organic degradation by electronic mediators.The research uses copper（Cu）and Atrazine（ATR）as representative heavy metals and refractory organics,the specific research contents and results are as follows:1.Study the effect of copper-atrazine compound pollution on soil MFC power generation and pollutant removal,and analyze the interaction mechanism between pollutants on the performance of soil MFC.Three experimental groups of copper pollution,atrazine pollution and copper-atrazine compound pollution were set up.The research results show that:for the removal of copper,compared with the copper pollution experiment group,the copper-atrazine composite pollution experiment group has higher ion content in the soil,and obtains lower soil MFC internal resistance and higher soil MFC power generation performance.It promotes the migration of acid extractable copper in MFC,and the interaction of the two pollutants in compound pollution causes atrazine and acid extractable copper to compete for adsorption sites in the soil,which promotes acid extractable state.The desorption of copper from the soil improves the mobility of heavy metal copper.Therefore,the total copper migration and removal rate of compound pollution（25.83%）is higher than that of copper pollution（16.84%）;For the removal of atrazine,there is no significant difference（P>0.05）between the atrazine removal rate of compound pollution（44.47%）and single atrazine pollution（53.11%）.This is because compared with the atrazine pollution experiment group,although the composite pollution experiment group has a higher ion content,but because a variety of pollutants are more toxic to the anode microorganisms,its electricity generation performance and atrazine pollution There is no significant difference between the experimental groups,so the efficiency of atrazine in the soil MFC through the biochemical reaction of electrons being reduced and removed is basically the same.2.The optimization mechanism of external regulation on the simultaneous removal of soil MFC organic-heavy metal compound pollution was studied.Three different external resistances of 10Ω,500Ωand 1000Ωwere selected to simulate the different voltage/current conditions of MFC,which uses MFC’s regulation of voltage/current to improve the purification efficiency of pollutants.Since the removal of copper in the soil MFC is mainly realized by the electromigration mechanism to the cathode under the action of its internal electric field,and the reduction reaction occurs at the cathode,the migration of copper is affected by the strength of the electric field inside the soil MFC.Under the conditions of a given electrode spacing,the higher the output voltage of the soil MFC,the greater the strength of the internal electric field is.Therefore,when the regulated voltage is the largest（external resistance 1000Ω）,more acid extractable copper can be driven to migrate to the cathode,and finally reach the highest total copper removal rate（25.21%）and the best cathode reduction effect.The removal of atrazine in the soil MFC is mainly achieved by getting electrons to undergo a reduction reaction,and the probability of atrazine contacting electrons is determined by the flow of extracellular electrons to the anode,and the output current reflects the direction of electrons.The removal of atrazine in the soil MFC is mainly achieved by the reduction reaction of electrons obtained at the anode,and the probability of atrazine contacting electrons is determined by the flow of extracellular electrons to the anode,and the output current reflects the direction of electrons.The amount of flow of the anode,so when the regulation current is at the maximum（10Ω）,more extracellular electrons flow to the anode,which increases the probability of atrazine electrons being reduced and removed.Atrazine was carried out in the experiment for 73 d.The highest removal rate is 76.08%.3.Humic acid improves the electricity generation performance of soil MFC by accelerating the electron transfer rate between the soil and the anode,thereby promoting the degradation of atrazine.And the higher the concentration of humic acid,the stronger the promotion effect of atrazine removal.In the experimental group of 10 g humic acid/500 g original soil,the removal rate of atrazine was 74.62%,which was higher than 2.5 g humic acid/500 g original soil（50.87%）.Minerals mainly promote the transfer of extracellular electrons through the oxidation-reduction reaction of variable-valent metals.Fe₃O₄significantly improves the electricity generation performance of MFC.The electron transfer and transfer efficiency in the system is higher,which makes it easier for atrazine to be reduced and removed by electrons.The removal rate of atrazine is higher,which reached to 63.35%within 63 days;while Mn O₂ has a low content of variable valence metals involved in the oxidation-reduction reaction and does not significantly promote the electron transfer process,so that it has a weaker effect on the electricity generation performance of MFC and has a small promotion effect on the removal rate of atrazine.