| With the advancement of technology and the improvement of people's material life,electronic products are in an era of high-speed replacement.Along with this is the generation of a large amount of electronic waste,some of which have caused a series of environmental pollution problems due to irregular disposal.The environmental damage caused by e-waste has become one of the hot spots in the field of environmental science.At present,there is not much research on soil contaminated by heavy metal with high concentration of electronic waste at home and abroad,so it is very important to study the remediation technology applicable to heavy metal pollution with high concentration.Common repair methods are physical,chemical and biological.Among them,electric repair is a safe and efficient repair method,and microbial repair in the biological method is also a repair technology that has emerged in recent years.Although it has good environmental benefits,it has the disadvantage of slow repair speed.This study combines electric repair technology and microbial repair technology,which can not only provide new ideas for the research of soil pollution remediation in China,but also accord with the development trend of soil remediation technology in the future.This article focuses on the research of remediation technology focusing on the heavy metal contaminated soil caused by the electronic waste recycling process.The main metals targeted include Cr,Cd,Cu,Zn,and Ni.In the experiment,Acidithiobacillus ferrooxidans(hereinafter referred to as A.f bacteria)was used to rinse the soil contaminated with heavy metals with a high concentration,and the heavy metals in the soil were dissolved by the leaching reaction of A.f bacteria.These heavy metals are migrated to the electrode cathode under the action of a micro-electric field,and the heavy metals in the soil are removed by precipitation,complexation,electroplating,etc.in the electrochemical reaction,so as to achieve the purpose of quickly repairing the soil contaminated with heavy metals of high concentration.In this experiment,the soil near the dismantling site of electronic waste was sampled.Under the action of a micro-electric field,the flask culture method was used to enrich and domesticate A.f bacteria.The concentration of heavy metals in soil was monitored by inductively coupled plasma emission spectroscopy(ICP-AES).The domesticated A.f bacteria were used to perform single-factor experiments on contaminated soil to study the reaction mechanism and survival conditions of A.f bacteria under the action of electric field.Orthogonal experiments are designed to obtain the optimal experimental parameters for this study,which lays a theoretical foundation for the future engineering application of this repair technology.The following main conclusions are obtained through experiments:(1)Discovered through experiments under the action of a micro-electric field.After 5 d,under the condition of applying a weak electric field of 20 m A,A.f bacteria had an electrode diameter of 6 mm and a solid-liquid ratio of 1:20.The removal rates of Zn,Cu,Ni,Cd,and Cr in the soil were not higher than those of the applied electric field The blank control of inoculation increased by 74 to 91%,58 to 72%,62 to 78%,57 to 85%,and 46 to 56%,respectively.This is because the electric field can stimulate A.f bacteria under the appropriate current intensity conditions.Multiply,accelerate the migration of heavy metals,and get better removal of heavy metals.Compared with the blank control group without the electric field,the removal rate of heavy metals can be increased by 20?62%.Among them,the improvement effect of Cu is the most obvious,from 10% to 72%,because A.f bacteria need a certain growth cycle.It is not possible to obtain a high removal rate of heavy metals in a short period of time.Under the action of an electric field,Cu is more active than other metals and is more likely to form electrodeposition,so as to obtain a better removal effect.(2)Through single-factor experiments with different current intensities,it was found that the removal rate of heavy metals by A.f bacteria was not significantly improved after 5 days under the condition that the current intensity exceeded 60 m A.When the current intensity exceeds 60 m A,the entire experimental system will be dominated by the electric field.Such current intensity will inhibit the removal of heavy metals from the soil by A.f bacteria.This is because the resistance of the A.f bacteria used in the experiment to the weak DC current reached the limit,thereby inhibiting the redox reaction and reproduction of A.f bacteria.(3)Through orthogonal experiments,it was found that when the solid-liquid ratio is 1:20mg/m L,the electrode diameter is 8 mm,the current intensity is 10-20 m A,and the amount of graphite powder is 0.1 g/L,the The removal rate is the highest.The remaining concentrations of heavy metals Zn,Cu,Ni,Cd,and Cr in the soil were 501±50,350±5.2,12±1.4,2±0.1,and 184±12.8 mg/kg,respectively.The concentrations of Cu,Ni,and Cd in the soil after removal were lower than the second-class land use risk screening values of 2000,150,and 20mg/kg.The concentration of kg and Cr is lower than the paddy field risk screening value of250 mg/kg in the Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard(Trial)(GB15618-2018),and it can meet the expectations of efficient removal of heavy metals.(4)If this research is applied to soil remediation projects,the target of remediation needs to be contaminated soil with high concentration of heavy metals or contaminated soil with high solid-liquid ratio.The secondary leaching experiment on soil found that the secondary leaching can effectively improve the effect of electric field on the removal of heavy metals by microorganisms under high solid-liquid ratio,and the removal rates of heavy metals Zn,Cu,Ni,Cd,and Cr reached 79%,respectively.,67%,82%,56%,42%,compared with a single rinse condition,an increase of 20 to 25%.This is because the newly added 9K medium provides nutrients for A.f bacteria,thereby improving the removal rate of heavy metals.(5)Because this study is in an acidic environment,the graphite electrode will corrode,reducing the electrode diameter and reducing the removal rate of heavy metals.After replacing the electrode with an iron electrode,the experiment was performed under the same conditions.The research results show that after replacing the iron electrode,the removal rates of Zn,Cu,Ni,Cd,and Cr are 46%,61%,16%,46 %,5%.After replacing the graphite electrode,the removal rates of heavy metals reached 97%,91%,97%,95%,and 63%,respectively.Because a small amount of rust Fe2O3 adheres to the surface of the iron electrode,the conductivity of the electrode is deteriorated,thereby weakening the effect of the electric field.In summary,replacing the iron electrode will greatly reduce the removal rate of A.f bacteria by 30 to 70%.The research results show that under the action of micro-electric field,A.f bacteria removal of heavy metals in soil from electronic waste treatment sites is an environmentally friendly,secondary pollution-free,efficient and convenient bioelectrochemical repair method,which can effectively solve the speed of soil repair by microbial methods.Slow question.It not only improves the removal efficiency of heavy metals in polluted soil,but also proposes new ideas for the practical application of combined electrochemical and microbial remediation of soil. |
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