Research On Removal Efficiency Of Heavy Metal In Soil By Microbial Fuel Cell

A brand new microbial fuel cell (MFC) which conbined favorable condition for constructing MFC on soil structure with the transferability of heavy metals in electric field, was built in soil environent. Through effective coupling of soil MFC producing electricity mechanism andtransferability of heavy metals, the way of using MFC to remove heavy metals in soil was achieved.Taking copper as the representative heavy metals, the desorption efficiency of Cu under different concentration、different pH、different water and soil ratio using EDTA-Na2、sodium citrate、citric acid、saponin was researched. The best desorption condition was decided eventually. The performance of soil MFC on electricity generation and removal efficiency on heavy metal Cu with desorption agent or with not was analyzed on this basis. And the influence factors such as external resistance, electrode spacing and soil pH on electricity generation and removal efficiency of Cu was also investigated. The results showed:(1)Using EDTA-Na2 of 20g/L at pH 7 as the best desorption condition was decided. Under this condition and 40% moisture content of soil, the soil MFC was successfully built. During the 70 days experimental period,5 electricity production cycles were formed, and the maximum voltage of 365mV and the internal resistance of 941.66Ω with EDTA-Na2 were provided, while the maximum voltage of 279mV and internal resistance of 941.66Ω with not EDTA-Na2 were achieved. It means The addition of EDTA-Na2 improved the generation of electricity and decreased internal resistance of soil MFC.(2)The concentration of water soluble Cu in soil MFC was reduced with time, it means that Cu content transferred from soil increased with time. At the end of this experiment, Cu removal efficiency in closed-circuit soil MFC with EDTA-Na2 was 23.62%, higher than the open-circuit soil MFC with EDTA-Na2 of 6.17% and the closed-circuit soil MFC with not EDTA-Na2 of 8.67%. The results showed the obvious advantages of the addition of EDTA-Na2 and the generation of electricity in improving the removal efficiency of Cu. The pH of closed circuit soil MFC increased gradually from anode to cathode after remediation, The pH of anode is about 7.0 and the pH of cathode is about 8.3, while the pH at different parts of open circuit soil MFC is similar, it is about 7.5.(3)The output voltage increases when the external resistance goes up, while the current gets lower. For a long-time running soil MFC, the closer its external resistance is to internal resistance, the lager power density could be. The removal efficiency of Cu in soil has positive correlation relationship with output voltage. In the range of 100mm to 80mm, narrowing electrode spacing could increase the electricity generation of soil MFC. And below this range, narrowing electrode spacing was not conducive to the electricity generation. The internal resistance was ascended with the narrowing of electrode spacing. The removal efficiency of Cu was affected by both output voltage and electrode spacing. The longer the electrode spacing is, the longer migration path of Cu will be, then the removal efficiency of heavy metal will be declined. The soil MFC got the highest electricity at initial nutrient solution pH 7, and the lowest electricity at initial nutrient solution pH 3. The internal resistance was maximum at initial nutrient solution pH 3, While the internal resistances of other three soil MFCS were almost the same. The removal efficiency of Cu was affected by both output voltage and the initial pH of initial nutrient solution, The removal efficiency of Cu was 14.46%、19.79%、27.96、13.63% respectively when initial nutrient solution pH was 3、5、7、9. The higher the pH of soil is, the lower content of water soluble Cu will be, the higher content of acetic acid extraction of Cu will be.(4) Last, the fundamental research of soil microbial fuel cell for soil contaminated by heavy metals are summarized and the future directions are presented.