Vol. 44, No. 2, Spring 2010 157

AccordingtoAccreditationBoardforEngineeringandTechnology (ABET) outcome 3d, graduates fromengineeringprogramsmusthavetheabilitytofunc-

tiononmultidisciplinaryteams.[1]Unfortunately,evaluationshows thatengineeringstudentsarenotwellpositioned tounderstandnewconceptsfromavarietyofdisciplinesandintegratethemintowhattheylearnintheirowndisciplines.[2]Thisisespeciallytrueforconceptsinemergingareas,suchaslifesciences.Obviouslytheemergenceoftechnologicalbreakthroughsinnewarenasisstimulatingfacultymemberstoincluderelatedmultidisciplinaryconceptsintheircoursedesignssothatstudentscanbepreparedtomeettheindustrialchallenges presented in applying new technologies withinindustrialsettings.[1]

Motivated by the lack of appropriate tools that can beusedtoteachchemicalengineeringundergraduatestudents,especiallytoteachthemhowtointegratelifesciencesand

THE MICROBIaL FUEL CELL aS aN EdUCaTION TOOL

ChE curriculum

aLim dewan, Bernard Van wie, and haLuk BeyenaL

Washington State University • Pullman, Washington 99164-2710zBiGniew LewandOwski

Montana State University • Bozeman, Montana 59717-3980

Alim Dewan is a graduate student at Washington State University, in the Gene and Linda Voiland School of Chemical Engineering and Bio-engineering. He earned his B.Sc. and M.Sc. in chemical engineering in 2002 and 2005, respectively, at the Bangladesh University of Engineering and Technology. His research interests include microbial fuel cells and electrochemically active biofilms.

Bernard Van Wie earned his Ph.D. in chemical engineering in 1982 from the University of Oklahoma, Norman, where he focused on blood-cell separations. He is now a professor at Washington State University, in the Gene and Linda Voiland School of Chemical Engineering and Bioengi-neering. His current research focuses on bioprocessing and biomedical engineering with applications in biosensors, cell culture, and biomass processing. In 2009, he received the Martin Smith Award as the most innovative instructor at the university.

Zbigniew Lewandowski received his M.Sc. in 1969 from the Technical University of Gliwice, Poland, and his Ph.D. in environmental engineer-ing from the Institute of Environmental Engineering, Polish Academy of Sciences, in 1976. He is now a professor in the Department of Civil Engineering, Montana State University, Bozeman, and head of the Biofilm Structure and Function Group at the Center for Biofilm Engineering.

Haluk Beyenal received his B.Sc., M.Sc., and Ph.D. degrees in chemi-cal engineering in 1990, 1993, and 1997, respectively, from Hacettepe University, Turkey. He worked as a postdoctoral researcher and then as an assistant research professor in the Biofilm Structure and Function and Bioelectro-chemistry Groups at the Center for Biofilm Engineering. Currently, he is an assistant professor at Washington State University, in the Gene and Linda Voiland School of Chemical Engineering and Bioengineering.

© Copyright ChE Division of ASEE 2010

engineeringconcepts,wehavedevelopedthemicrobialfuelcelleducationmodule(MFCEM),ahands-onlearningmod-ulethatcanbeusedforlearningmultidisciplinaryconceptsinanactivegroup-learningmodality.Thismoduleusestheprinciplesofmassandenergyconversionsappliedinami-crobialfuelcell(MFC)tointegratevariousconceptstaughtinbiology,chemistry,electrochemistry,andengineering.Inthispaper,ourgoal is to show how the MFCEM can beusedasanaidinteachingasenior-levelcourseinchemi-calengineering—IntroductiontoBioprocessEngineering(ChE475).Figure1showsthecomponentsofthemoduleandhowweimplementeditintheclassroom.

Figure 1. Methodology for implementing the microbial fuel cell education module.

Chemical Engineering Education158

MICROBIaL FUEL CELL EdUCaTION MOdULEClasslectureswereusedtointroducethetheoryofvarious

processesimportanttounderstandingmicrobialrespiration,thethermodynamicandkineticprinciplesoftheprocessesinvolvedinenergyconversioninMFCs,andthebasiccalculationsusedinelectricalengineering(e.g.,currentandpower).Thehands-onworkconsistedoftheoperationofanMFCinthelaboratory.Forthelaboratoryexercises,wepreparedamanualtoinstructthestudentsaboutsafetyissues;equipmentneededtorunthe

TABLE 1The Concepts, Related Topics, and Mathematical Expressions Introduced Using the MFCEM

Concepts Specific topics Mathematicalexpression* Reference

CellularrespirationMicrobialgrowthkinetics

•Metabolicpathway•Electrontransportchain•Redoxreactionsinrespiration•Microbe-solidinteractions•Monodkinetics

dX

dtX

S

K S

X

Y

S

X S

dSdt

SK SS

=+

=−+

µ

µ

max

max

/

[6,9]

Electrodepotential(Electrochemicalequilibrium)

•Nernstequation

E EM

M

E E

A M

o ox

red

C

o

= +

= +

( )( )

0 059

2

0 059

402

.log

.logg

1

2

4

p Ho⋅ +

[6,7,10]

Overpotential(Electrodekinetics)

•Butler-Volmerequation•Electrodepolarization

i i

F

RT

F

RT= − −+

0

0 5 0 5exp

.exp

.η η

[6,10]

Current •Faradayconstant•CalculationofcurrentfrommaterialbalanceandgrowthkineticsinMFC

Faradayconstant=electricalchargeofanelectron×Avogadroconstant

I

V

Rext

=

[7]

Power •Differencesbetweencurrent&powerandenergy&power

P V I

V

RI R

ext

ext= ⋅ = ⋅=

22

[7]

Chargeconservation • Faradic efficiency

εc

t

I dt

F nS

M

=∆

∫0

[7,11]

Energyconservation • Energy efficiency•MaterialandenergybalanceforMFC

εE

t

c in

ext

t

c in

V I dt

H m

I R dt

H m=

⋅

∆=

⋅

∆

∫ ∫0

2

0

. .

[7]

Sustainability • Definition of sustainability•SustainabilityofpowergenerationinMFCs –

[12,13]

*Detailsonthedevelopmentoftheseequations,andexamplecalculationsusingexperimentaldata,wereincludedintheMFCEMhandoutgiventothestudents.

MFC,withphotographs; step-by-stepprocedures, alsowithphotographs;sampleexperimentalresults;samplecalculations;and final-report requirements. The students, assembled into two groups,rantheMFC,computedtheenergyconversion,andpresentedtheresultstotheirclassmates.Debates,moderatedbytheinstructor,ontheresultsobtainedbythevariousgroups,wereaimedatreinforcingtheconceptsdiscussedinthelectures.Last,weassignedasetofproblemstotestunderstandingoftheconceptsandtoevaluatetheroleofthehands-onactiveexperienceintheclassroom.

Vol. 44, No. 2, Spring 2010 159

TheincorporationoftheMFCEMintothebioprocessen-gineeringcourse,ChE475,gaveusanopportunitytoteachtheconceptsthroughanactive-learningprocess.Comparedtostandardlecture-based,passivelearning,thehands-onactive-learningprocesshelpsstudentstovisualizeandmorefullythinkthroughwhattheylearnandhelpsthemtomakeconnectionsbetweenconceptsthattheylearnedbefore.[3]Asclaimedinthewell-knownlearningretentionpyramid,[4]studentsrememberconceptsbestwhentheyseeademonstration(50%),engageinadebateordiscussion(70%),orhaveachancetodosome-thingrealandapplytheirknowledgeimmediately(90%).WiththeMFCEMweparticularlyemphasizedpracticebyrunningexperimentsthatwereanimmediateapplicationofthein-classlectureandhavingthestudentspreparereports,performhome-workassignments,andholdin-classdebateswiththeactiveinvolvementoftheotherstudentsintheaudience,whoaskedquestionsorexpressedopinionsononesideortheotherofthedebate.TheremainderofthematerialinChE475wastaughtinapassivemanner,withtheprofessorlecturingandthestudentstakingnotesandcompletinghomeworkassignmentsbasedontheirnotesandreading.WeexpectedthattheintroductionoftheMFCEM into our course would significantly increase learning retentionofthetopicsinChE475andofthemultidisciplinaryconceptsintroducedbytheMFCEM.

IN-CLaSS LECTURE: THEORYIntheChE475course,weusedBioprocess Engineering,

writtenbyShulerandKargi(2002).[5]Aftercompletionofthe first six chapters students were familiar with the funda-mentalsneededtounderstandMFCsandwethenintroducedmultidisciplinaryconceptsusingtheMFCEM.Wedonotdiscuss all the concepts in this paper because of spacelimitations;however,theywerediscussedinconsiderabledetailintheclassroomandintheMFCEMmanualgiventothestudents.Whilesomeoftheconceptshadbeentaughtinpreviouscourses,wereintroducedthemsothatstudentscould connect the new concepts with previously learnedconcepts.The concepts, related topics, andmathematicalexpressions[6-8] that were introduced using MFCEM aresummarizedinTable1.

Thetopicswerepresentedbyaskingaseriesofquestionsand helping the students find the answers. The following paragraphspresentselectedquestionsweaskedandgiveabriefdiscussionofhowtheywereimplemented.

How did the scientist who ran the first MFC think to use microbes?OurtheorysectionstartedwiththisquestionanditwasactivelydiscussedintheclassroominagroupformattogivethemainideabehindtheMFC.Thenweintroducedtheconceptofhowasinglecellgrows,duplicates,andgainsenergy.Weshowedasinglecell(Figure2A)anddescribedthemainideabehindMFCs,whichisseparatingtheoxidationandreductionreactionsintherespirationsystem.Aftershow-ingFigure2A,weaskedthestudentstobuildanMFC.The

studentsworkedtoseparatethetwoenvironmentsandmaketheMFCdepictedinFigure2B.ThisprocesshelpedthemtounderstandthebasicprincipleoftheMFC,thatofseparatingtheoxidationandreductionreactionsusingaproton-exchangemembrane(PEM)andconnectingthetworeactionenviron-mentsthroughanexternalcircuit.Laterwediscussedindetailandexplainedwhyweneedtouseaproton-exchangemem-brane(Figure2B).Thishelpedthestudentsbetterunderstandwhatacathodeandananodeare.Theylearnedthatoxidationhappensattheanodeandreductionatthecathode.

How are the electrons transferred from bacteria to the solid electrode?Theinteractionofmicrobeswithsolidmaterialsis a fascinating new topic, not only in MFC research butalso in microbiology and environmental science. Electrontransfermechanismswereintroducedandthestudentsweretaught why electrons cannot jump directly from microbestosolidsurfaces,i.e.,thatelectronsmustbetransferredbyaredoxreactionvia:1)amediator,achemicalthatacceptselectronsresultingfromthemicrobialrespirationprocessandtransfersthemtothesolidelectrode,orperhaps2)linkageofthemicroorganismswiththeelectrodesurfacebynano-wiresorcytochromes.Thestudentswereexcitedaboutthesetopics,whichconstitutecutting-edgeresearchquestions inmicrobiology.

What are the source of and the sink for the electrons?Thisquestionwasansweredbyrevisitingthemajormetabolicpath-wayconcepts,taughtearlierinthecourse.Weshowedhowelectronsarederivedfromthemicrobialrespirationsystemandtransportedtoanelectronacceptor(inthiscaseasolidelectrode)throughtheelectrontransportchain.Thisusedtobeamundanesubjectforthestudents,butnowtherewasa

Figure 2. The original idea of a microbial fuel cell de-scribed using a single cell. (A) The redox reactions—oxi-

dation and reduction—in the microbial energy generation process. (B) The separation of the oxidation and reduc-tion reactions, using a proton exchange membrane, to

build a microbial fuel cell.

Chemical Engineering Education160

real-lifeapplicationforthemetabolicpathwaysandthereforetheyappearedtobeengagedinthesubjectasevidencedbytheenergydemonstratedbystudentswhentheyexpressedtheirideasandthecontentoftheirgroupdiscussions.Tofurtherfacilitatediscussions, theideaofusingtwodifferent typesofbacteriawasintroduced—oneusinglactateandtheotherusingglucoseastheelectrondonor.

What do we mean by the electrode potential, current, energy, and power of a fuel cell?The electrodepotentialsare thermodynamicproperties andare calculatedusing theNernst equation (Table1).Whencurrent ispassed throughtheelectrode,however,thethermodynamicequilibriumdoesnotexistanymore;rather thecurrentneedstobecalculatedusingtheButler-Volmerequationdescribingelectrontransferkinetics.Asaresultofthisdiscussion,thestudentsimprovedtheirunderstandingofthedifferencesbetweenequilibriumandnon-equilibriumprocesses.Theconceptofoverpotentialisvitaltounderstandingbatteries,fuelcells,corrosionprocesses,andelectrochemical sensors.Using theMFCEM, studentswereintroducedtotheconceptsofpolarizationcurves(cellpotentialvs.current)andoverpotential.Inaddition,theylearnedbasicelectrical engineering concepts suchas electrical potential,current,power,andenergy,andhowtoperformmeasurementsforandcalculationsoftheirvaluesinMFCs.

How much electrical charge or how many electrons can we derive from microbial reactions?Thisquestionwasaskedtoin-troduce the concept of Faradic efficiency. The students learned howtocalculatethemaximumpossiblenumberofelectronstransferredasaresultofthedifferencesinoxidationstatesofchemicalsandtheconcentrationsofchemicalsinthegrowthmedium.Studentshad todomaterial balances to calculateFaradic efficiency. Discussions resulting from this question helpedtointroducetheconceptofchargeconservationinelec-trochemicalsystemsandtheFaradayconstant(Table1).

How much power can be harvested from an MFC for a given amount of substrate?Thecalculationofpowerfromcurrentandpotentialhelpedstudents tounderstandsimpleelectricalengineeringconceptsandtaughtthemthediffer-ences between potential and current, and between powerand energy.These concepts often confuse students in theelectricalcircuitcourserequiredduringtheirundergraduate

studies.Thus,theMFCEMallowedthemtointegrateelec-tricalengineeringconceptswithchemicalandbiochemicalengineeringconcepts.

How sustainable is power generation in an MFC?Studentsareoftenexposedtogeneralterms,suchasthesustainabledevelopmentoftheeconomyofacountry,andtheyneedtoextend the application of the term “sustainable” to powergenerationinMFCs.SustainabilityofpowergenerationinMFCs is defined as the ability to generate power at a constant rateoverlongperiods,anditisevaluatedbymonitoringtheenergy production and consumption using different loadsontheMFC.Thereisnogeneralcriterionbywhichonecellproducespowerinasustainablemannerandanotherdoesnot:italldependsontheratioofthepowergeneratedtothepowerconsumed.Whentherateofenergyconsumptionishigherthantherateofenergygenerationbythemicroorganisms,theMFCdoesnotproducepowerinasustainablemanner.Theoppositeistrueaswell,however,theMFCproducespowerinasustainablemannerwhentherateofenergyconsump-tionislowerorequaltotherateofenergygenerationbythemicroorganism.[14]

HaNdS-ON WORK: ExPERIMENTS We had nine students run the experiment (selection of

studentswasonavolunteerbasis),andthegroupofexperi-menterswasdividedamongtwoteams,eachofwhichwasas-signedoneoftwooptions.OneteamrantheMFCexperimentsusingShewanella oneidensiswhiletheotherusedKlebsiella pneumoniae.Thegoalofusingtwodifferentmicroorganismswastoobservethedifferenceinpowergenerationandlatertoarrangeadebateontheroleofthedifferentrespirationsystemsinaccountingforthatdifference.Duringtheexperimenteachteamtestedtheeffectsoftheselectedvariable(microorgan-isms,seeTable2).Toimplementthepedagogyincrowdedclasses,multiplegroupscouldbeusedandeachgroupcouldbesubdividedintosmallerteams:eachteamwouldinvestigateone of the variables listed in Table 2 and report their findings backtotheirothergroupmembers.Thispaperdescribesourclassroomexperience, inwhichonlyonegroupconsistingoftwoteamsworkedonunderstandingtherolesofdifferentmicroorganismsinMFCs.Theremaining14studentsreceived

informationvialecture,fromlisten-ing todebatepresentationsby thetwogroups,andfromparticipationduringandafterthedebatethroughasking questions and expressingtheirownopinions.

At the end of the experiments,theteamspreparedreportsandgaveclass presentations.The presenta-tionshadtheformatofadebate.Thetwoteams,whichhaduseddifferentmicroorganisms, compared their

TABLE 2 Experimental Conditions, Variables Tested, and Topics for the Debate

Variable (for groups)

Conditions in the MFCs (for teams)

Topics for debates between teams

Microorganisms 1.Shewanella oneidensis2.Klebsiella pneumoniae

Cellularrespiration

Electrodematerial 1.Graphite2.Stainlesssteel

Microbe-solidsinteraction

Substrate 1.Glucose2.Naturalbiomass

Renewableenergysource

Load 1.Lowresistor2.Highresistor

Sustainability

Vol. 44, No. 2, Spring 2010 161

powergeneration.Debatescenteredaroundwhyoneofthemicroorganismsproducedmorepower than theother, andateam’spositionhadtobesubstantiatedusingthecalcula-tions shown in the theory section. We noticed significant involvementofthestudents,interestingquestions,andmanyrecommendationsonhowtoincreasethepowergenerationinsuchdevices.

Construction of the MFC.Toruntheexperiments,studentsusedatwo-compartmentMFC.ThecomponentsoftheMFCandthestepsrequiredtoconstructitareshowninFigure3.Thecompartmentsweremadeofpolycarbonate(8cm×8cm×3.7cm)andwerefurnishedwithopeningsatthetoptomakeelectricalconnectionswiththeelectrodes.Cationexchangemembrane(ESC-7000,ElectrolyticaCorporation)wasusedtoseparatethecompartments.Thecoverplatesweremadeofpolycarbonateandhadthreeopeningsforinletandoutlettubingconnections.Topreventleakage,rubbergasketswereusedbetweencompartmentsandbetweenthecompartmentsandcoverplates.Screwswithwingnutswereusedtoholdthereactortogether.Siliconerubbertubeswereusedtodeliverliquidsandgasesand to remove themfromthe respectivecompartments.Theelectrodesweremadeofgraphiteplates(GraphiteStore.com,Inc.)withsurfaceareasof23cm2fortheanodeand63.4cm2forthecathode.Thesewereplacedagainstthecationexchangemembrane,paralleltoeachother.

ToconstructtheMFC,studentsfollowedthestepsshowninFigure3.Thestepsare:1)insertingtheelectrodesintothecompartments,2)placingagasketontheinnersideofeachcompartment,3)placingthecationexchangemembraneover

the first gasket, 4) placing another gasket on the other side ofthemembrane,5)puttingthecompartmentstogether,6)placinggasketsoutsideofthecompartments,7)placingthecoverplates,8)holdingthecompartmentsandcoverplatestogetherusingwingnuts andbolts, and9) connecting thetubing and then autoclaving the MFC.After autoclaving,the reactorwascooleddown to roomtemperatureand theanode and cathode compartments were filled with anolyte andcatholyte,respectively.Theanodewasinoculatedwiththeselectedbacteriaforeachgroup.Theninstep10studentsplacedthereferenceelectrodeinthecathodiccompartmentandconnectedtheelectricalwire,resistor,etc.Thesestep-by-stepproceduresaredescribedinawrittenmanual,anditisavailableuponrequestfromtheauthors.

aSSIGNMENTSTheassignmentsweredesignedtoevaluateunderstanding

ofthemultidisciplinaryconceptstaughtusingtheMFCEM.Inconstructingassignmentquestionsweconsideredthedif-ferentlevelsinBloom’staxonomy[15]andthelevelsoflearnerknowledgedescribedbyApple andKrumsieg(2001)[16] thatareexpectedtobeevidentinresponsesgeneratedbycollegegraduates.WesummarizetheassignmentproblemsinTable3(nextpage),andmatchtheassignmentswithlevelsinBloom’staxonomyandwithAppleandKrumsieg’s levelsof learnerknowledge.Thequestionsarediscussedinthefollowingsec-tions; however, becauseof space limitationswegiveonlyselectedanswershere.Thefullrangeofanswersisavailableuponrequest.

Figure 3. Major com-ponents used and steps followed to construct the microbial fuel cell used by the students.

Chemical Engineering Education162

The first problem was designed to determine whether the studentsunderstoodtheprinciplesoftheprocessandcouldperformbasiccalculationsquantifyingprocessesinMFCs,electrochemistry,andelectricalcircuitry.SolvingthisproblemrequireduseofBloom’slevelsofknowledge,comprehension,application,andevaluation,andAppleandKrumsieg’scor-respondinglevelsoflearnerknowledge,asshowninTable3. InProblem1a, the studentsdescribed thebasic ideaofMFCs using their knowledge of microbial respiration andtheelectrontransportmechanisms.Inpart1b,theyusedtheconceptsofmaterialbalanceandchargebalancetocalculatecurrent,power,currentdensity,andpowerdensity.Inpart1c,thestudentsusedtheirconceptualunderstandingofelectri-cal circuits and material balances to calculate the amountof glucose required to produce sufficient energy to power a lightbulbforonehour.Inpart1d,theywereaskedtothinkcreativelyandapplylearnedconceptstoMFCs.Thisproblemalso tested the students’ ability to integrate concepts fromelectricalengineeringwiththosefromchemicalengineeringandapplythemtoscalingupadevice.Inpart1ethestudentswereaskedtodiscussthefutureofMFCsandevaluatetheirpotentialforprovidinganalternativeenergysource.

The second problem was designed to relate conceptssurroundingcell-growthkinetics inbioreactorswith thoserelevanttoMFCs,bothofwhicharetaughtinthiscourse.This problem was designed to include the analysis andsynthesis,andevaluationlevelsofBloom’staxonomy,andthecorrespondingworkingexpertiseandresearchlevelsofAppleandKrumsieg’staxonomy.Inpart2a,studentswereaskedtodevelopamathematicalmodeltoquantifyvariationsinsubstrateconcentrationandpowergenerationover timeandtoconstructtheplotsshowninFigure4Aand4B.Thispartwasdesignedtodeterminewhetherstudentscouldinte-gratetheideaoftheFaradayconstantwithmassandenergyconservationslaws,whicharetaughtinphysicalchemistry/electrochemistry and basic chemical engineering courses.Constructing the plots inFigure 4 required the solving ofsimultaneous first-order differential equations, using concepts taughtinoursophomore-levelnumericalmethodscourse.Part2brequiredthecalculationofpowergenerationusingdifferentvaluesformicrobialgrowthkineticparametersandcolumbicefficiency. Figure 4C shows how power generation and the timetoreachthemaximumpowerdependontheMonodkineticcon-stant (Ks).The studentsneededto draw plots similar to that inFigure4Ctoevaluatetheeffectsofthemaximumgrowthrateandthe columbic efficiency. This part of theproblemwasdesigned toevaluatethestudents’abilitiestointerpretthephysicalmeaningofthegrowthkineticparametersinthecontextof theMFC.Inpart

TABLE 3Levels in Bloom’s Taxonomy and Apple and Krumsieg’s Levels of Learner Knowledge

Used in Constructing Questions to Evaluate Learner Performance in the MFCEMLevels Bloom’s level[15] Apple and Krumsieg’s level

of learner knowledge[16]Problems as-signed

I Knowledge Information 1b,2a

II Comprehension ConceptualUnderstanding 1a,1c

III Application Application 1d

IV,V AnalysisandSynthesis Workingexpertise 2a,2b,2c,2d

VI Evaluation Research 1e,2d

2c, the students discussed how the columbic efficiency would changeifanexternalelectronacceptor(oxygen)werepresentintheanodiccompartment.Thisquestionwasaskedtoassesstheirunderstandingofhowelectrontransportisinvolvedinthe microbial respiration system. Part 2d was open-endedandmatcheswithBloom’s levelsVandVI, synthesisandevaluation,respectively,andAppleandKrumsieg’sLevelV,research.Inthispartstudentswereabletoassessthevariationinpowergenerationasafunctionofactualprocessvariablesincludingtemperature,pH,andconductivity.

aSSESSMENT OF THE MFCEMTheassignments(Box1,pg.164)couldbecompletedif

the students could successfully integrate multidisciplinaryconcepts.Forexample,toconstructamodelequation(Prob-lem2a)for thesubstrateconcentration,currentandpowergeneration in a batch MFC, students needed to integratetheconceptsofmicrobialgrowthkinetics,massandchargeconservation, and Faradic efficiency.

The effectiveness of the MFCEM was assessed by: 1)comparisonoftheresultsoftheassignmentscompletedbythestudentswhohadrunhands-onexperimentswiththoseofstudentswhohadnot;2)ourobservationsduringtheexperi-mentalactivityandthedebate;and3)thestudents’comments.Sincethestudentsrunningtheexperimenthadvolunteeredweexpectedthemtobemorecurious,takemoreinitiativeandbeself-motivated,andthereforetobebetterpreparedtolearntheMFCconcepts.Weindeedfoundthistobetrue,astheyearned42%morepointsonaveragethanthestudentswhodidnotruntheexperiments.Theresultwasshowntobe statistically significant using a 95% confidence level (α =0.05)andthenullhypothesisthatthetwoaveragesweredifferent.Inatwo-tailedt-testwith18degreesoffreedomthep value was 0.019 (<α). Also, there were several interesting observationsmadeduringthedebatebetweenthetwoteamsdoingtheexperiments:

1) The students discussed aspects of microbial respiration and the electron transport processes, including concepts for which scientists are still trying to find answers;

2) Current and power calculations were vividly discussed, and one of the students even commented that “potential,

Vol. 44, No. 2, Spring 2010 163

current, energy, and power concepts finally made sense” to him; and

3) Many students who previously were silent in class were effectively involved in the discussions.

Weareawarethatourstudyislimitedandamoredetailedassessment of the effectivenessof this tool is needed.Weexpecttocollectmoredataintheupcomingsemesters.First,itwillbeimportanttocomeupwithotherperformancemea-suresbesideshomeworkassignments;wewilllikelyincludeacritical-thinkingrubricbeingdevelopedinothercompanionwork,[17]conceptinventoriesthatourgroupwilldevelopbasedonsimilarstrategiestakenbyStreveler,etal.(2008).[18]Also,itwillbeimportanttoeliminatethepossibilitythatonlythemore motivated students elect to participate in the active

experimentalaspectofthecourseandthatsuchstudentsarealreadyinclinedtowardamoreindependentlearningcompo-nent.TosafeguardagainstthiswewillorganizestudentgroupsbyrandomselectionorbasedonafairlyequaldistributionofGPAsbetweenstudentswithintheactiveexperimentalgroupsandthoseexposedtopassivelectures.Wecouldalsohaveasecondexperimentalactivityofequivalentrigorinwhichthestudent groups are switched: those that first did experimental activityandformeddebatesquadswouldonlyhavethepassivelectureforthesecondexperiment,andviceversa.Finally,adetailedsurveyonstudentperspectivescouldbeusedinwhichthestudentsthemselvescomparethelearningenvironments,theirgrowthinunderstanding,andtheirabilitytoworkwithothergroupmembersindependentofinstructorinput.

Figure 4. (A) Microbial cell concentration and substrate concentration vs. time plotted using the model equation derived in Problem 2a. (B) Current vs. time calculated for Problem 2a. (C) Power generation vs. time calculated for various Monod

constants (Ks). Similar figures were plotted by the students to show the effects of the maximum growth rates and columbic efficiencies.

Chemical Engineering Education164

bOX 1: Problems assigned after introducing the MFCEMProblem 1.Inacontinuousmicrobialfuelcell(MFC)thecellsaregrownintheplanktonicphase,anaerobically,using

glucoseastheelectrondonor,andtheelectronsaretransferredtothesolidelectrodeswithoutanykineticlimitation.

SupposethecellgrowthratecanbedescribedbyMonodkineticsas

rS X

Sx=

⋅+

0 90 7..

Atasteadystate,thesterilegrowthmediumisfedatarateof1L/h.Theworkingvolumeoftheanodiccompartmentof the MFC (the liquid volume) is 10 L. The inlet glucose concentration is 2 g/L and the cell yield coefficient (Yx/s)is0.5.Electronsarederivedfromthesubstrateaccordingtothefollowingreaction.

C H O H O CO H e6 12 6 2 2

6 6 24 24+ ⇒ + ++ −

a) Can you explain why and how the electrons are transferred from cells to the solid electrode? b) Calculate how much current can be produced if the Faradic efficiency is 1.0 (all the derived electrons are transferred to the

solid electrode). If the cell potential is maintained at 0.5 V, what will the power produced by the MFC be? What will the current density and power density be if the anode surface area is 5 m2 and the Faradic efficiency is 1.0 at an average cell potential of 0.5 V?

c) How much glucose would be needed to power a 60-W light bulb for an hour, if the power generation were the same as that in part a?

d) MFCs are an energy source characterized by low power generation. If the energy generation of the MFC remains the same as that calculated in part a, how would you scale up an MFC to harvest sufficient energy in two hours to power a laptop for one hour? Note that an Apple Mac laptop operates at 97 watts.

e) How feasible is it to design a MFC that will power a laptop directly? Can you predict the future for MFCs as an alternative energy source?

Problem 2.Alaboratory-scalebatchMFCisstartedwithacellconcentrationof0.1g/Linananaerobicanodechamberwithavolumeof0.25L.Thegrowthkineticparametersareµmax=0.9hr-1andKs=0.4g/L.Theinitialsubstrate(glucose)concentrationis1g/L.ThecellgrowthcanbedescribedusingMonodkinetics,andthesubstrateconsumptionrateis

− =dSdt

XY

x s

µ.

/

whereµ is the specific growth rate, X is the cell concentration and the cell to substrate yield coefficient Yx/sisassumedtobeequalto0.7.

a) Construct a mathematical model to quantify the variation of substrate concentration, current, and power over time. How long

will it take to consume 90% of the substrate? What will the concentration of cells be at that time? When will the MFC produce a maximum current? What would the maximum theoretical power be if the cell potential could be maintained at 0.8 V?

b) What would happen to the power generation if the Monod half rate constant (Ks), the maximum growth rate, and the Colum-bic efficiencies were different?

c) What inference can you make about the Faradic efficiency if the anode chamber is aerobic instead of anaerobic?d) Qualitatively predict the variation of power generation with the variation of reactor temperature, pH, and conductivity.

Vol. 44, No. 2, Spring 2010 165

CONCLUdING REMaRKSWesuccessfullydevelopedandimplementedtheMFCEM

toteachtheconceptsofmicrobialrespiration,electrochemicalequilibriumandkinetics inafuelcell,chargeconservation,energy,current,andpower.Thesenior-levelbioprocessengi-neeringcoursewasappropriateforincorporatingourMFCEM.InitialassessmentsbasedonstudentassignmentsgivestrongsupportiveevidencethattheMFCEMisaneffectivetoolforteachingmultidisciplinaryconceptsandthatactiveexperimen-tationsurroundingitsimplementationissuperiortolearningthrough apassive lecture.Expanded activities and amorerigorouslearningassessmentareplannedforthefuture.

aCKNOWLEdGMENTSTheauthorswouldliketothanktheGeneandLindaVoil-

andSchoolofChemicalEngineeringandBioengineeringforstartupfundsinsupportoftheresearch(Dr.Beyenal)andtheInstitutional Review Board (IRB) of the Office of Research AssurancesatWashingtonStateUniversityforapprovingtheresearchstudyandprocessingtheexemptiondeterminationapplication.The authors gratefully acknowledge the U.S.Office of Naval Research (ONR) (Grant #N00014-06-1-0217)(activitiesthroughthisgrantlaidthegroundworkforthe UFCM), the National Science Foundation Grant #DUE 0618872(activitiesthroughthisgrantlaidthegroundworkforthehands-onapproachanditsassessment),and3MonthedevelopmentofMFCEM.

NOMENCLaTURE EA Anodepotential(Volts) EC Cathodepotential(Volts) E

M0 Standardreductionpotentialofmediator(Volts)

EO2

0 Standardoxygenreductionpotential(Volts) F Faradayconstant(coulombs/moleofelectrons) i Net current flow to/from an electrode (A) io Exchangecurrent(A) I Currentthrougharesistor(A) Ks Growthconstant(g/L) Mox Mediatorconcentrationatoxidationstate(mole/L) Mred Mediatorconcentrationatreductionstate(mole/L) min Inlet flow rate of fuel (moles) n Numberofmolesofelectronsproducedpermoleoffuel P Power(Watt)PEM ProtonExchangeMembrane P

O2 Partialpressureofoxygen(atm)

Q Inlet flow rate (L/hour) Rext Externalresistor(ohms) R Universal gas constant (J/mole/˚K) S Substrateconcentration(g/L) So Initialsubstrateconcentration(g/L) T Temperature (˚K) t Time(sec) V Potentialdropacrosstheresistor(Volts)

X Cellconcentration(g/L) Xo Initialcellconcentration(g/L) Yx/s Yield coefficient ΔS Rate of substrate consumption (g/hour) ΔHc Heatofcombustionoffuel(J/mole) εc Faradic efficiency εE Energy efficiency µ Specific growth rate (1/hour)µmax Maximum specific growth rate (1/hour) η Overpotential (V)

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