INTERNATIONAL UNIVERSITY HCMC SCHOOL OFBIOTECHNOLOGY REPORT FINAL PROJECT Microbial Fuel Cell For Wastewater Treatment Contents I. INTRODUCTION.. 2 II. WASTEWATER COMPOSITION.. 4 III. PROCESS.
5 IV. ROLE OF MFCS. 13 V. ADVANTAGES & DISADVANTAGES. 14 VI. APPLICATION OF MFC SYSTEM IN BREWERY WASTEWATER.. 14 VII.
CONCLUSION.. 18 VIII. REFERENCES. 19 I. INTRODUCTION 1.
General informationContaminated wastewater sources give rise toenvironmental pollution (on the surface or underground water bodies). Wastewatertreatment has become a major concern in many countries due to its benefit asdrinking source for human and this is a crucial solution, a basic sanitation toprotect environment.Many phenomena including eutrophication ofsurface waters, hypoxia, and algal blooms impairing potential drinking watersources are specific consequences of direct disposal of unprocessed watergenerating from domestic, agricultural, industrial and small-scale facilities.Yet the ways to overcome these environmental impacts have not much yieldeddesired efficiency.Rapid industrialization and overgrowth ofpopulation are two main causes that current wastewater treatment technologiesare not sustainable to meet the ever-growing water because those energy- andcost-intensive techniques are dominant over for development of technologiesthat are energy-conservative or energy-yielding. For the present and future context,microbial fuel cells (MFCs) technology, which presents a sustainable and anenvironmental friendly route to solve the water sanitation problems, may becomeone of most noticeable technique for wastewater treatment.
Microbial fuel cell (MFC) – employ theconcept of bioelectrochemical catalytic activity in whichmicrobes/bacteria are main characters that produce electricity from theoxidation reaction of organic (in most cases), inorganic (some cases), andsubstrates collected from any urban sewage, agricultural, dairy, food andindustrial wastewaters. As shown in many researches, MFC technologycould be highly adaptable to a sustainable pattern of wastewater treatment forseveral reasons: (1) Abilityto have a direct recovery of electric energy and value-added products(2) Combinationof biological and electrochemical processes => Achieve a good effluent quality and lowenvironmental footprint (3) Inherentof real-time monitoring and control => Benefit operatingstability. Fig.1. Microbial Fuel Cells produce energy while consume food sources fromwastewater 2. Objective of a projectThe potential for energy generation andcomprehensive wastewater treatment in microbial fuel cells are discussed.
An overview of MFC application on brewerywastewater treatment is mentioned with two specific aims:1) Providea background of current energy needs for wastewater treatment and potentialenergy recovery options followed by a nutrient content in wastewater and acomprehensive review of the principles of wastewater treatment, substrateutilization (organic removal).2) Presentprocess performance, organic removal capacities. Fig.2.CleaningOkinawan pig farm wastewater with MFCs containingtreated and untreated wastewater from the Okinawa Prefecture Livestock andGrassland Research Center MFCs in the OIST Biological Systems Unit labII. WASTEWATER COMPOSITION The composition of the microbial fuel cellfor waste water treatment are shown detail following this figure: Fig.
3. MFC forwastewater treatment with two chambers of cathode-anode. Microbes fed onvarious compounds in wastewater sources and transfer electron to the cathodechamber to be used to produce useful chemicals or remove environmentalpollutants.
Forexample: Brewery Wastewater TreatmentBrewery and food manufacturing wastewatercan be processed by MFCs because there is a rich content in organic compoundsthat can serve as food for the microorganisms. Breweries are ideal for theimplementation of microbial fuel cells, as they remain a steady and stableconditions for easily bacterial adaptations due to their sane wastewatercomposition and thus is more efficient. Moreover, organic substances in breweryunprocessed water are biodegradable, highly concentrated which helps to improvethe performance of fuel cells. III. PROCESS · MFC is bioreactorthat undergoes the catalytic reaction to convert chemical energy in the chemicalbonds in organic compounds to electrical energy by microorganisms underanaerobic condition or capture electrons from electron transport chains byinorganic mediator forming. Fig.
4.Typical type of microbes can utilize almost any chemical as a food source. Inthe MFC system, bacteria form a biofilm, a living community that is attached tothe electrode by a sticky sugar and protein coated biofilm matrix. When grownin an anaerobic condition, the byproducts of bacterial metabolism of waste compriseof carbon dioxide molecules, electrons and hydrogen ions. Electrons generatedby the bacteria are shuttled onto the electrode by the biofilm matrix, creatinga thriving ecosystem called the biofilm anode and producing electricity. · As opposed to excess sludge and energy issues in conventionalwastewater treatment systems, a better solution to eliminate is to convert directly waste into cleanelectricity with high value energy or chemical products. This biologicalsystem is known as bioelectrochemical system (BES).
· Bioelectrochemicalsystems produce clean energyfrom waste organic substances by applying indigenous exoelectrogenic bacteria,in which the energy is extracted in the form of bioelectricity in MFCs orvaluable biofuels such as ethanol, methane, hydrogen, and hydrogen peroxide incase of microbial electrolysis cells. · A cation exchangemembrane also known as protonexchange membrane (PEM) is used for anode and cathode compartments separationand permeability of proton ions to anode chamber. · Electrons releasingin anode chamber will combine withhydrogen ions and oxygen forming water through electrical circuit.· Where are the microbes in aMicrobial Fuel Cell? o Microbes accept electrons fromorganic matter – Electron donors (e.g.
acetate:a reducing agent)o Microbes donate electrons toreducible chemicals – Electron Acceptors (e.g.oxygen: an oxidizing agent) o In MFC, anode is an electronacceptor o This below figure shows thickbiofilm on wastewater fed microbial fuel cell The principle of MFC: mostly based on redox reactiono MFC system includes:an anode, a cathode, a PEM and an electrical circuit. o Substrates act asmicrobial feed that use in MFC are glucose, acetate, acetic acid and so on,influence the overall performance which can be justified by CE (coulombicefficiency) and P (power density) parameters.o Wastewaters providinga good source of organic matter for electricity production and wastewatertreatment accomplishment simultaneously have been used for MFC system toeffectively offset the operation costs for treatment processing.o An MFC is a galvanic cell and the based system is exergonic fromelectrochemical reactions.o Energy is released from the reaction and thus it possessesnegative free reaction energy (Gibb’s free energy). The standard free energycan easily be converted into a standard cell voltage (or electromotive force,emf) DE0 as shown inEq.
(1). § Where: v DG0 (J/mol): free energies of respective products and reactantsformation.v n (moles): stoichiometry factors of the redox reactionv F Faraday’s constant (96,485.3 C/mol). § The Gibbs free energy of a reaction measures the maximum amount ofuseful work obtained from a thermodynamic reaction.
§ The theoretical cell voltage or electromotive force (emf) of theoverall reaction indicates anode and cathode potential differences, leading todetermination the electricity generation capacity in a system in Eq (2). o In an MFC, the Gibbs free energy of the reaction is negative. Thus,the emf is positive, which represents the spontaneously potential electricitygenerates from the reaction. For example, if acetate is used as the organicsubstrate with oxygen reduction, the oxidation-reduction reaction would beshown in Eqs. (3)- (5): · Oxidation – reductionreactions (ORR) in MFCs o Pollutants in the wastewater composed of organic substances andother nutrient products and also metals are sources to produce clean and directelectricity through oxidation-reduction reactions § where electron release, transfer and acceptance under biochemicalor electrochemical processes at the anode and cathode electrodes occur. § one acts as an electron donor while the other must serve as anelectron acceptor. § the chemical compounds, that take responsibility for electronsaccepting, are known as terminal electron acceptors (TEA). o The following redox reactions, a substrate (electron donor) andother substances such as nitrates, phosphates, and others as electronacceptors, as shown in (Eqs.
(6) – (18)), introduce some possible bioelectrochemical reactions in MFCs electricitygeneration and wastewater utilization spontaneously.§ Oxidation reactions (anode) § Reduction reactions (cathode) · Materials and methods o For example: Beer brewery wastewater Ø Wastewater and Organic Substrates.ü Pollutants arecollected from brewery manufacturing wastewater.ü Wastewater is usedas the inoculums for the reactor and as substrates.ü Organic substrateswill consume glucose as a reducing agent. ü Nutrients, minerals,vitamins stock solution and a phosphate buffer (PBS) are components in medium. Ø Operationü The system will runin a temperature controlled room (room temperature)ü The reactor willinoculate with wastewater in continuous flow mode operation. Ø Analysesü The COD measurementsof the wastewater and other organic compounds will be recorded, according tostandard method.
ü The chart belowsummarizes the procedure for COD concentration. ü The change in cellvoltage and the parameter for generating power over the resistor at a constantresistance are continuously monitored during digestion time using digitalmillimeter.Ø Electric power calculationü Power density(conversion of recorded voltage at an interval of time): unit of electric powerin MFC system§ Anode/cathodeunit (W/m²) = U x J current density = I / A (A/m2)§ Power density pervolume of MFC unit (W/m³) = 1000U x J x A / 0.1§ Where: vA: surface area ofanode/cathode (m2)vP: power density(W/m²), (W/m3)vJ current density(A/m2)vU: voltage yield (V)vR: externalresistance (?)v1000: unit changev0.1: volume ofanolyte (L) ü Coulombic efficiency(CE): displays electricity production and electron transfer from substrate toelectrode (generate energy as product) performance. It is estimated byintegrating the measured current to theoretical current based on the consumedCOD § CE = CE / CT x 100%vCT =(Fxnxw)/MvCE = Ixt§ Where:vCT:theoretical current productionvCE:actual current productionvI: current of MFC(A)vt: time elapsedbetween feedings of the anode (s)vM:molecularweight of substrate (g mol?1)vn:number of moles of electrons exchanged per mole of substrate (n=4 in CODwastewater)vF: Faraday’s constant (C/mol) (F= 96485 C/mol)vw: DCOD removed daily (mg/L) Ø Microbial community in the MFC enrichmentü As can be seen fromthe electron microscopes, the fuel cell electrode had a microbial biofilmattached to its surface with loosely associated microbial clumps.
• Microscopy • Low-vacuumelectron micrographs (LVEM) • Scanning electronmicrographs (SEM) • Transmissionelectron microscopy (TEM)• Confocal scanning laser microscope (CSLM) ü Images of MFCbiofilms in four micrographs Ø Communitystructure of the MFC: Identify byü Bacterial 16S rRNAgene librariesü Denaturing gradientgel electrophoresis (DGGE) analysis => Anaerobic cultivationØ Expected resultsü Biological wasteswill be degraded in MFC system as well as electricity products from brewerywastewater treatment.ü Improvement on researchthat yields high efficiency to treat wastewater =>A possible result to scale-up for practical application. IV. ROLE OF MFCS · Organic removalo Synthetic wastewater as substrates (acetate, glucose, sucrose,xylose and other organic substrates for microbial oxidation): carbon removal(>90%) is high from wastewaters in the anode chamber.o Actual wastewater as substrates (low BOD, low energy densitycarriers or feed stocks): still capable of treating high strength wastewatersthanks to anaerobic conditions in the anode chamber.
o Effect of process parameters: in terms of substrate conversionrate, depending on: § Biofilm establishment, growth, mixing and mass transfer trends inthe reactors§ Bacterial substrate utilization-growth-energy gain kinetics (mmax: maximum specific growth rate of the bacteria, and Ks: bacterialaffinity constant for the substrate)§ Biomass organic loading rate (g substrate per g biomass presentper day)§ Proton exchange membrane efficiency§ Overpotentials due to electrode surface, electrochemicalcharacteristics, electrode potential, kinetics, electron transfer mechanism andthe current.§ Internal resistance § Membrane resistance to proton migration · Nutrient removal o Efficiently removed in biocathode chambers =>Enhance the effluent water quality o Recovered as NH4+ or MgNH4PO4.6H2O,preferred to struvite. · Metal removal o Non-biodegradable: Utilized as electron acceptors => Reduce andprecipitate. o If incorporated: Equip the ability to remove and recovery heavymetal ions in wastewater. V. ADVANTAGES & DISADVANTAGES 1.
AdvantagesThere are several advantages that are concerned:§ Applicationof MFC technology to sustainable wastewater treatment yield positive efficiency§ Electric energy can directly extractfrom organic matters in wastewater§ Achievingthe power whilewastewater is treat § Show a better decontaminationperformance, especially for removal of aqueous recalcitrant contaminants including manypersistent contaminants. § Have a low carbon footprint § Typicallydeveloping of microorganism into a biofilm on electrodes in MFC show their goodresistance to toxic substances and environmental fluctuations. 2.
Disadvantages§ Bacterialmetabolic losses§ Lowpower density § Highinitial cost § Limiteduse, only use for dissolved substrate VI. APPLICATION OF MFC SYSTEM IN BREWERY WASTEWATER 1. Characteristics of beer brewery wastewater 2. Set up double chambers MFC consisted of twochambers that are constructed with 6 cm×5 cm×6 cm in size, each chambercontained a liquid working volume of 0.1 L and separated by a proton exchangemembrane (PEM). Fig.5.
Sequentialanode-cathode MFC diagram Anode: three parallel groups of carbonfibers, which were wound on two graphite rods (?8 mm, 5 cm long) to form 3-sheetstructures (4 cm×3 cm)Cathode: plain carbon felt (6 cm×6 cm, 3mm thick with biofilm). In the bottom, an aerator was inserted to supply airand mixing.Inlet and outlet with respect to everyside constructed at both anode and cathode, while on the top, six electron tipjacks with a diameter of 9mm were set up.
Associations between two electrodeswere aggravated for copper wires through a rheostat (0. 1–9999 ?). The externalresistance (R): 300 ?.
The cell voltage(V) of the MFCs: 50mVThe MFC was worked in continuous flow atroom temperature. Raw brewery wastewater was pumped to the anode chamber withthe up-flow rate (13.6 ml/h), matching to a hydraulic retention time (HRT) of7.35 h.
Effluent of anode was joined by a beaker,and then it was pumped into the cathode chamber with the same flow rate withHRT 7.35 h. 3. Calculationsa. Electricalparameters in practical § Accordingto Ohm’s law, the current density and power density were calculated at R=300?and U= 0.
02 V that yielded from MFC long-term operation_ Current density:At anode electrode: A = 6 cm×6 cmx3 = 108cm2 =0.0108m2 J = I/A =U/ (RxA) = 0.02 / (300×0.0108) = 0.006 (A/m2)At cathode electrode: A’= 4 cm×3 cm = 12cm2 = 0.
0012m2J = I/A =U/ (RxA) = 0.02 / (300×0.0012) = 0.
056 (A/m2) _ Power density:At anode electrode: A = 6 cm×6 cmx3 = 108cm2 =0.0108m2 P = 1000U x J xA / 0.1 = 1000×0.02×0.
019×0.006 / 0.1 = 0.0228 (W/m3)Atcathode electrode: A’= 4 cm×3 cm =12cm2 = 0.0012m2 P =1000U x J x A / 0.1 = 1000×0.02×0.
056×0.0012 / 0.1 = 0.01344 (W/m3)§ Coulombic efficiency (CE) was determined by:o In day 1for NH3 – N in wastewater: influent of COD was 1299 mg/L and effluent CODof anode chamber was 657 mg/L. According to the practical, MFC operation wasrecorded with the feed cycle time is 24 hour (86400s): CE = CE/CT x 100% = (Ix t) / (F x n x w) / M x 100% = (0.
02/200 x 86400) / 96485 x 4 x (1299-657)/ 17 x100% = 172800/14574910= 1.19%b. Dataof wastewater on seven days: Data showed that:§ Effluent of anode was connected by a beaker,which kept an HRT of 7.35 for each chamber => overall HRT of this system was7.35+7.
35 = 14.7 h.§ Flow rate was 13.6 ml/h=13.6 /157.73 = 0.086 gal/day= 13.6×0.
024 = 0.3264 L/day, the same rate with influent and effluent.§ Overall influent in 7-days is 1292 mg/L (anaverage value of influent COD). Overall effluent in 7-day is 682 mg/L (anaverage value of effluent COD of anode, because the treated water was releasedin anode column) ? % Removal efficiency = (Removed/Influent x 100%) = (Influent-Effluent)/Influent x100% ð %Removal in anode chamber = (1292- 682/(1292) x 100% = 47.2%.
§ Influent COD fluctuated from 1249 to 1359 mg/Lcorresponding to organic loading rates (OLRs) of 4.08–4.43 kg COD/(m3·d)in 0.1L of working volume. The organic loading rates corresponding to 1249 mg/LCOD influent was calculated by: ð Organic loading rate=COD in(kg/L)xFlow rate (L/day)/Reactor volume (m3) = (1249×10-6×0.
3264)/ (0.1×10-3) = 4.08 kg COD/(m3.d)§ 91.7%–95.
7%is the overall removal efficiencies value that reached, while donations ofanode chamber were 45. 6%–49. 4% 1.86–2.
12 kg COD/(m3·d) to substratedegradation rates (SDRs), which represent over a half extent. The substratedegradation rate indicates the rate for COD removal during the cycle operationcorresponding to 1249 mg/L of COD influent that yielded 4.08 kg COD/(m3.d)in OLR by 45.6% COD removal from anode contribution was measured by: ð Substrate degradation rate=OLR x %substrate removal efficiency at t time = 4.
08 x 45.6% = 1.86 kg COD/(m3.
d) c. Discussion:§ At an external resistance of 300 ?, a steady CODremoval efficiency of both chambers (91.7%–95.7%) was attained.
§ Moreover, R=300 ?, an open circuit voltage of0.434 V and a power density includes 0.01344 (W/m3) vs. cathodic area and 0.
0228 (W/m3)vs. anodic area) were attained.§ With a high COD removal efficiency, it isconcluded that the sequential anode-cathode MFC constructed with bio-cathode inthis experiment could provide a new approach for brewery wastewater treatment.§ HRT value was 14.7h (>10 h) for the wholesystem indicating the effectiveness of MFC wastewater treatment.§ In this study, since the influent COD of cathodewas high (650–710 mg/L), the excessive COD entering the cathode may be causedthe inferior electrochemical performance of the MFC. In addition, the lowcathodic open circuit possibility for ?0.034 V also pointed a sign of incipientCOD carry-over.
Thus, optimization should be carried out further to improve theperformance of this sequential anode-cathode MFC. VII. CONCLUSION Microbial fuelcells show the potential for a sustainable route to mitigate the growing energydemands for wastewater treatment and environmental protection. The indigenousexoelectrogenic microbial communities in the MFCs are capable of degradingvarious forms of wastewaters.
However, until now, researchers are trying toimprove this system to get highest effectiveness and reducing as much aslimitation. The following issues should be given priority for significantdevelopments in MFC technology such as incorporating effectively between lowcost materials and cost-effective electricity production in MFCs; wastewatersshould be the focus of future research and process development activities; morein-depth studies focusing on life cycle impact analysis of the microbial fuelcell technology should be developed to identify critical areas of development. VIII.
REFERENCES 1. Wastewater treatment in microbialfuel cells – an overview Veera Gnaneswar Gude, Department of Civil &Environmental Engineering, Mississippi State University, Mississippi State, MS39762, USA 2. Wastewater Treatment withMicrobial Fuel Cells: A Design and Feasibility Study for Scale-up in Microbreweries, Ellen Dannys, Travis Green,Andrew Wettlaufer, Chandra Mouli R Madhurnathakam and Ali Elkamel 3. Electricitygeneration and brewery wastewater treatment from sequential anode cathodemicrobial fuel cell, QingWen,YingWu,Li-xinZhao,QianSun,and Fan-yingKong