The Preliminary Study Of Using Double Chambers And Mediator-less Microbial Fuel Cell As BOD Sensor

Organic pollution is a major aspect of water pollution, at the meanwhile, biochemical oxygen demand (BOD) acts as an important indicator of organic pollution. Now, some existing determination methods have some general disadvantages such as long-time determination, narrow measurement range and bad reproducibility. Thus, the quick and accurate BOD determination comes to be a hard problem in the area of environmental monitoring. Using MFC as BOD sensor can achieve this determination of the target water's BOD, for the advantages as fast response, large measurement and high stability.A double chambers and mediator-less type MFC was designed in this study, whose cathode and anode consist of 3mm graphite felts with 7% porosity, and the two chambers were separated by a high intensity Nafion117 proton exchange membrane. Sediments from anaerobic digestion tank in Xiao Hong Men sewage treatment plant were used as initial microorganisms and the inoculating quality was 10 ml. At the stage of start-up, a fed-bath of electricity generation was used to domesticate bacterium, the nutrient solution with 500 mg/L BOD was added, whereas the glucose solution with 200 mg/L BOD was added in the later domestication, and a steady current of about 30μA generated after 430 hours, while the peak time was about one hour and the response time was 20 hours.The effecting factors such as the external resistor, the temperature condition, pH, buffer types and buffer concentration, oxidant type and its ventilation rate were studied. The results showed that, when the pH was 7, the temperature was 25℃, the phosphate's concentration was 0.1mol/L, and the O2's aeration rate was 100ml/min, the MFC got the best working condition.The designed MFC was used as BOD sensor, and the measuring range of BOD was determined as 0-200mg/L, and the BOD could be determinated by the max current when less than 50 mg/L, while by the whole coulomb generated when the BOD was between 50 mg/L and 200 mg/L, which illustrated that the types and the numbers of the electrochemical bacterias, the stable operation time, the design and the materials used can generate critical effect on the production of electricity of the MFC, and also indicated that the discovery of more efficient electrochemical microorganisms and the design of more efficient MFCs would be important contents of the study of BOD sensors in the future.