Study On The Electricity Production Performance Of Soil Microbial Fuel Cell And Its Remediation To Cd Contaminated Soil

Microbial Fuel Cells(MFCs)is one kind of environmentally friendly remediation technique that converts chemical energy into electrical energy.It can generate small amounts of electricity without consuming energy.MFC which use soil to produce electricity is called soil MFC.This paper mainly studies on the soil MFC about its properties of the electricity production and its remediation to Cd contaminated soil.It investigated the different influences respectively,such as microbial species and inoculation mode,Cd pollution concentration,external resistance and distance between anode and cathode.The main conclusions are as follows:(1)According to different inoculating modes,single-chamber soil microbial fuel cells(MFC1,MFC2,MFC3,MFC4 and MFC5)were constructed with the mixed culture(anaerobic sludge)and the single strain(Geobacter sulfurreducens)as electrogenesis microorganism.The result showed that MFCl had the shortest startup time which was 2d.It had the best performance of electricity generation that its maximum power density was 35.08mW/m2 and the resistance was 515.5Q.The effect of soil remediation was related to the performance of electricity generation.MFC1 had the best Cd accumulation ratio which was 19.02%.In this experiment,the best startup conditions was the inoculate mode of anaerobic sludge being concentrated on the anode electrode.It was found that the stable operation of the MFC reactor would promote the accumulation of heavy metal Cd at the cathode to achieve the purpose of soil remediation.(2)The single-chamber soil MFC reactor was constructed with four Cd pollution concentrations,respectively,Omg/kg,5mg/kg,20mg/kg and 100mg/kg.As a result,the electricity production performance of the reactor with Omg/kg Cd concentration was better than the other three reactors,indicating that the toxicity of Cd had a bad effect on the activity of the anaerobic sludge as the electro-microorganism.The internal resistance of the four reactors was almost same,which was around 2000?.With the increase of Cd concentration,the accumulation ratio in the cathode was becoming smaller.The reactor with 5mg/kg Cd concentration had the best accumulation ratio in the cathode,which was 130.00%.Among the forms of Cd,the weak acid extractable state had accumulated to the cathode obviously,and reducible state,oxidazable state and residue state of Cd in the cathode were the same as before.The open ciruit reactors which as the control group didn't have any effect due to the lack of current.(3)The single-chamber soil MFC reactor was constructed with four external resistances,respectively,10?,100?,100?,1000?.As a result,MFC-10000? had the largest output voltage.The maximum power density of these four groups had a little difference,the reactor with the bigger external resistance would reach the maximum power density under the larger current density,and the maximum power density was higher than the reactor with small external resistance.The internal resistance of the four reactors was almost the same.About the soil pH and the remediation of Cd in soil,it showed that the cathode soil pH of MFC-10000? increased to 8.35 obviously,and had the best Cd accumulation ratio in the cathode,which was 128.49%.However,the cathode soil pH of MFC-10? had a little change,which was 8.13,and the accumulation ratio in the cathode of Cd was the lowest,42.19%.Among the forms of Cd,the weak acid extractable state had the best accumulation to the cathode.(4)The single-chamber soil MFC reactor was constructed with three kinds of distance between cathode and anode,respectively,3cm,6cm and 9cm.As a result,MFC-9cm had the maximum output voltage.It also showed that the gap of the output voltage between MFC-3cm and MFC-6cm was less than the reactors with MFC-3cm and MFC-9cm.It was shown that the larger distance between cathode and anode,the effect on the output voltage of soil MFC would be more obvious.MFC-9cm had the highest maximum power density,which was 13.65mW/m2.The internal resistance of each reactor had a great difference.Comparing the cathode soil pH and the accumulation ratio in the cathode of Cd for these three groups,it was found that the cathode soil pH of MFC-3cm increased obviously,and the accumulation ratio of Cd was 107.70%,which was the best.The open ciruit reactors as the control group didn't have any effect due to the lack of current.