Study On Low Cost BOD Sensors Basing On Activated Carbon-air Cathode Microbial Fuel Cell

Biochemical oxygen demand(BOD)is a measure of biodegradable compounds in water and is a common parameter to design and assess the performance of wastewater treatment plants.BOD is also applied in water quality monitoring.The conventional method to measure BOD is time consuming(5 or 7days),requires trained personnel and cannot reflect the degree of pollution of water immediately.Microbial fuel cells(MFCs)have emerged as a new method to determine the BOD,which is based on the electricity production respiratory metabolism of bacteria to convert organic matter into an electrical current.In some condition,MFCs generally give good linear correlation between current or charge and organic pollutants concentration.While there are some limitations of MFC-type biosensor such as with noble metal as electrode catalyst material;with an expensive proton exchange membrane structure;continuous aeration on cathode and so on.The MFC described in this paper without noble metal catalyst,proton exchange membrane or oxygen exposure device could convert biodegradable mater into an electrical energy directly.This single-chamber MFC was constructed with an activated carbon-polytetrafluoroethylene(PTFE)air cathode and a carbon felt anode.A rudimentary MFCs in a 20 ? incubator with a 1 K? resistance,1 g/L acetate as fuel and activated sludge as inoculum generates maximum power 420 mW·m-2 while the maximum current density is 2.03 mA·cm-2 and maximum open-circuit voltage is 550 mV.The sensor was calibrated with an aerated nutrient medium containing acetate as the BOD source.Linear correlation(R2= 0.97)with charge was obtained for BOD concentrations ranging from 80 to 1280 mg/L in a reaction time of 50 h.This indicated that the sensor was able to adapt to different solution as substrate.In addition,to explore the relationship between resistance and measuring range as well as response time of the BOD sensors,different resistance were tested in this paper.Results showed that larger measuring range could be got if reaction time was extended and external resistor was increased.Moreover,with external resistor unchanged and reaction time shorten,the measuring range would be smaller.MFC-type BOD sensors in this paper is inexpensive.Its performance is higher than most of the similor sensors.The results are expected to promote the practical application of MFC based BOD sensors.