MICROBIAL FUEL CELL IN WASTE WATER TREATMENT

MICROBIAL FUEL CELL IN WASTE WATER TREATMENTKRISHNAKUMAR RM140475MENIT CMicrobial fuel cellBioelectrochemicalsystemthatdrivesacurrent byusingbacteriaandmimickingbacterialinteractionsfoundinnatureMFCscanbegroupedintotwo thosethatuseamediatorandthosethataremediatorlessThefirstMFCs, demonstratedintheearly20thcentury,usedamediator:achemicalthat transfer electronsfromthe bacteriainthecelltotheanodeMediatorlessMFCsareamorerecentdevelopmentdatingtothe1970sInthistypeofMFCthebacteriatypicallyhaveelectrochemicallyactiveon theiroutermembranethatcantransferelectronsdirectlytotheanodeSincethe21stcenturyMFCshavestartedtofindacommercialuseinthe treatment ofwastewaterHistoryM.Potterwasthefirsttoperformworkonthesubjectin1911 AprofessorattheUniversityofDurhammanagedtogenerateelectricityIn1931BarnetCohendrewmoreattentionwhenhecreateda microbialhalffuelcell ,whenconnectedinseries,werecapableof producingover35volts,thoughonlywithacurrentof2milliampsDelDucaetal.whousedhydrogenproducedbythe fermentationofglucosebyClostridiumbutyricumasthereactantat theanodeofahydrogenandairfuel cellSusuki made the improvement leading to the present design of fuel cells in 1970sTypes of microbial fuel cellsMediatormicrobialfuelcellMostofthemicrobialcellsareelectrochemicallyinactive.Theelectrontransferfrommicrobialcellsisfacilitatedbymediatorssuchasthionine,methylviologen,methylblue,humicacid,and neutralredMostofthemediatorsavailableareexpensiveandtoxic.MediatorfreemicrobialfuelcellMediatorfreemicrobialfuelcellsdonotrequireamediatorUse electrochemicallyactivebacteriatotransferelectronstotheelectrode MediatorlessMFCsare amorerecentareaofresearch Mediatorlessmicrobialfuelcellscan,besidesrunningonwastewater, alsoderiveenergydirectlyfromcertainplants.Thisconfigurationis knownasaplantmicrobialfuelcellThe MechanismWhenmicroorganismsconsumeasubstancesuchassugarinaerobicconditionstheyproducecarbondioxideandwater.However,whenoxygenisnotpresent,theyproducecarbondioxide,protons,and electronsC12H22O11+13H2O12CO2+48H++48e-Microbialfuelcellsuseinorganicmediatorstotapintotheelectron transportchainofcellsThemediatorcrossestheoutercelllipidmembranesandbacterialouter membraneItbeginstoliberateelectronsfromtheelectrontransportchainthat normallywouldbetakenupby oxygenorotherintermediatesIntroductionPower output of MFC depends on the oxygen concentration level in the cathodic chamberCritical oxygen concentration is 6.6 mg/L for a MFC with graphite cathodeOxygen in the cathodic chamber of MFC was always supplied by mechanical aeration or by atmospheric airA photosynthetic MFC is defined when sunlight is converted into electricity within the metabolic reaction scheme of an MFCSince the oxygen can be produced by growing algae in the sunlight, it is hypothesized that the electricity can also be generated by algal photosynthesis in the cathdic chamber of MFCMATERIALS AND METHODS Synthetic Wastewater and Sludge Source During the experimental period, the composition and the concentration of synthetic wastewater for MFC were 1000 mg/L glucose, 300 mg/L nutrient broth, 167 mg/L NaCI, 25 mg/L K2HP04, 25 mg/L NaH2P04, 5 mg/L FeCb, 100 mg/L MgCh, 10 mg/L MnS04, 133 mg/L CaCI2, 25 mg/L NaOH, and 175 mg/L NaHC03. The COD of synthetic wastewater was between 1002 and 1296 mg/L. Original sludge in MFC was obtained from an industrial wastewater treatment plant located in Ping Tung, TaiwanMFC Design and Operational ConditionsA dual-cell MFC was applied in this study. Both anodic and cathodic chambers were the same size, with an effective water volume of 797 cm3 Two same-sized graphite carbon electrodes were used for both anode and cathode (6.3 cm length X 4 cm width X 3 mm thickness)The anodic and the cathodic chambers were separated by a PEM (Nafion 117, Dupont Co., USA)The distance between the anode and the cathode was approximately 36.5 cmResearch was not to attain high power levels but to investigate the behaviors of MFC with algal photosynthesis in the cathodic chamber.

The MFC was operated at an ambient temperature of 24-26C It was run under a continuous flow condition at five different rates (350, 700, 1000, 1500, and 2000 L/min) For the anodic chamber, hydraulic retention times (HRTs) at the five different flow rates were 38.3, 19.1, 13.3, 8.9, and 6.6 h, respectivelySynthetic wastewater (influent) and effluents from the anodic chamber were collected for analysisThe performance of MFC system was considered stable when both COD removal efficiency and power output are stable. The flow rate was set to 350 L/min in Phase 1.The voltage of MFC was measured almost every day at external load resistance adjusted to 1000 ohm until the system was stableWhen the voltage readings became stable for a few days, influent and effluent water samples of MFCs and voltage readings during the last two days of Phase 1 were taken for COD analysis and power density calculation, respectivelyThe average COD concentration and the average voltage on both days were then used for the analysisThe duration of operation in Phase 1 was 27 days and the time required to reach stable was about 3 weeksSimilarly, MFC power production and water quality under the flow rates of 700 (Phase 2), 1000 (Phase 3), 1500 (Phase 4), and 2000 L/min (Phase 5) were evaluated. The durations of operation in Phase 2, 3, 4 and 5 were 11, 10, 9 and 16 days, respectively. The time required to reach stable for these Phases was about 7 days.Green algae (Chlorella) and blue-green algae (Phormidium) were grown in the cathodic chamber One gram of KH2P04H20 and one gram of NH4CL were added into the cathodic chamber to serve as nutrients for algae in the beginning of Phase 1Two 6 W fluorescent lamps (12 W in total) were installed 15 cm above the water surface of the cathodic chamber to provide the light for photosynthesis. Oxygen in the cathodic chamber was then produced by the photosynthesis of algae. Wastewater Treatment EfficiencyCOD removal efficiencies decreased and substrate degradation rates increased as flow rates increased from 350 to 2000 L/min. At lower flow rate, microorganisms in the anodic chamber had more time to degrade the substrate at lower flow rate and caused higher COD removal efficiency. However, as flow rate increased, the quantity of substrate entering the anodic chamber also increased. Therefore, the amount of substrate degraded by the microorganisms in the chamber (substrate degradation rate) increased as flow rate increasedRelationship between COD removal rate and COD loading can be expressed as a binary quadratic equation with the coefficient of determination (R2) of 0.9750. Similarly, a binary quadratic equation can also be used to express the relationship between COD degradation rate and COD loading (R2 = 0.9842).

Effects of Influent Characteristics on Power Production Binary quadratic equations can be used to express the relationships between voltage output and flow rate (R2 = 0.7809) and between power density and flow rate (R2 = 0.8368), with external load resistance of 1000 ohmSimilarly, the relationships between voltage output and COD loading (R2 = 0.8093) and between power density and COD loading (R2 = 0.8719) can also be expressed as binary quadratic equations, with external load resistance of 1000 ohm

Polarization CurvesPolarization curves were obtained at the end of each phase. Maximum power densities were about 0.78 mW/m2 (anode surface) with external resistance of 5000 ohm and current density of 5.20 mA/m2 (anode surface) at the end of Phase Iabout 0.50 mW/m2 with external resistance of 6000 ohm and current density of 3.93 mA/m2 at the end of Phase 2,about 0.97 mW/m2 with external resistance of 5000 ohm and current density of 5.14 mA/m2 at the end of Phase 3, about 0.83 m W/m2 with external resistance of 5000 ohm and current density of 4.51 mA/m2 at the end of Phase 4, and about 2.01 mW/m2 with external resistance of 5500 ohm and current density of 7.75 mA/m2 at the end of Phase 5. Maximum power density was much higher in Phase 5, where flow rate was higher

Coulombic Efficiency of MFCCoulombic efficiency can be used to express the efficiency of power production per unit of organic matter utilized by a microorganismNormally, the goal is to obtain higher power density and higher Coulombic efficiency in an MFC.The optimum COD loading rate to obtain higher power density and higher Coulombic efficiency in MFC (= 0.50 mW/m2 and 0.055 %) is about 2.00 kg m-3 day-1Therefore, for a wastewater treatment plant, optimum power output does not necessarily occur at higher organic loading rate. Higher organic loading rate may cause poor treatment efficiency. However, higher organic loading can obtain higher power output. Conclusionmicrobial fuel cell in wastewater treatment system by using algae as the oxygen supplier in cathodic chamber for power production can be feasible. However, it was found that oxygen concentration seems not very stable during the whole period of study and may be the reason for unstable electricity production efficiency at different COD loadings. Therefore, further studies should be required to obtain more stable and much higher power production in the future. THANK YOU!!