Final Exam.docx

Final Exam.docx

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FinalExam

53:

050

NaturalEnvironmentalSystems

FINALEXAM:

ClosedBook-ClosedNotes

May13,2010

NAME

1.（10pts）

Onemethodforremovinghardness（Ca2+）fromwaterisbyprecipitating（making）CaCO3（s）.If,afterestablishingequilibriumwithCaCO3（s）,thedissolvedCa2+concentrationis5mg/L（=1.25x10-4M）andthepHis10.1,

（a）WhatistheCO32-concentrationinmol/L?

3.66x10-5M

（b）WhatistheHCO3-concentrationinmol/L?

6.22x10-5M

（c）Whatisthealkalinityinmg/LasCaCO3?

13.1mg/L

2.（6pts）

Asolutionismadebyaddingcalciumphosphate（Ca3（PO4）2（s））topurewaterandallowingittocometoequilibrium.Assumethesystemisclosedtotheatmosphere.Writethechargebalanceequationforthiswater.Informationattachedtotheexamandthefollowingmaybeuseful.

Ca3（PO4）2（s）↔3Ca2++2PO43-pKs=27.0

3.（20pts）

Butyricacid（CH3CH2CH2COOH=HBt;MW=88）isaparticularlymalodorousacid（foundinrancidbutter,parmesancheese,andvomit（yuk!

）,andisalsothecauseofsomebodyodor）.HumanscandetectthesmellofHBtatconcentrationsofabout10ppmintheatmosphere.Typicallythewayweminimizeodorproblemsistoensurethatmostofthebutyricacid（TOTBt=[HBt]+[Bt-]）isintheionizedform（i.e.,Bt-）.

（a）Thetotalconcentrationofbutyricacid（TOTBt）inawatersampleis1,000mg/LasHBt（=1.14x10-2M）andthepH=5.5.WhatistheconcentrationofHBtinthiswaterinmg/L?

173mg/L

（b）Assumingthiswaterisinequilibriumwiththeatmosphere（totalpressure=1atm）,willtheaveragehumanbeabletodetecttheodorofbutyricacid?

Showallcalculationsnecessarytojustifyyouranswer.Ayesornowithoutsupportingcalculationswillreceivenocredit.NO（0.985ppm）

Thefollowingmaybeusefulinsolvingthisproblem:

HBt↔H++Bt-pKa=4.82

HBt（aq）↔HBt（g）KH=5x10-4L-atm/mol

4.（20pts）

Acompletelymixedreactoristobeusedtotreataleachate.Theleachatehasaflowof100m3/d,apollutantconcentrationof1,000mg/L,andistobetreatedina1,000m3CSTR.Aseriesofstudieshasbeenconductedtocharacterizethissystem.

（a）Ajartestisconductedtoassessthekineticsofpollutantremoval.Leachateisaddedtoareactor（the“jar”）andthereactionisallowedtoproceed.Resultsareshowninthefigurebelowentitled“JarTestResults”.

（1）Writethegeneralmass-balanceequationforthejartest.

（2）Whatistheratecoefficient?

Besuretoincludeappropriateunits.1.67x10-3L/mg-hr

（b）Atracerstudyisconductedtoassessreactorhydraulics.AslugofaconservativetracerisaddedtotheCSTRreactorandallowedtowashout.Resultsareshowninthefigurebelowentitled“TracerStudyResults.”

（1）Writethegeneralmass-balanceequationforthetracerstudy.

（2）WhatisthetruehydraulicretentiontimeforthisCSTRreactor?

Justifyyouranswer.6d

（c）YouaretodevelopapredictiveequationfortheCSTRtreatingtheleachateundersteady-stateconditions.

（1）Writethegeneralmass-balanceequationfortheCSTR.

（2）Usingappropriateassumptionsandsubstitutions,developanequationthatwillpredictthehydraulicretentiontimerequiredtoachieveatargeteffluentconcentrationatsteadystate.

（d）Usingthedatagivenintheproblemandyouranswersto（a）,（b）,and（c）,determineifthisCSTRwillachieveaneffluentpollutantconcentrationof50mg/L.Justifyyouranswerwithappropriatecalculations.

NO（need9.48d）

Additionalspacetoworkthisproblemisgivenonthenextpage.

5.（6pts）

（a）Brieflydescribethedifferencebetweenoligotrophiclakesandeutrophiclakes.

（b）WhichtypeoflakewouldhavethehighestDOduringthedayandwhichwouldhavethehighestDOduringthenight?

Why?

6.（4pts）

Briefly,whatarethereferencedose（RfD）andtheslopefactor（SF）,andhowaretheyusedbyenvironmentalengineers?

7.（10pts）

Twenty-eight（28）miles（45.1km）downstreamfromawastewaterdischarge,aportionofariveristobedivertedforuseinapondbeingconstructedaspartofapark.TheStateDNRpermitforthepondrequiresthatthedissolvedoxygen（DO）beatleast6mg/L.WillBODhavetoberemovedfromthewastewaterpriortodischargetotheriver?

Ifso,howmuchBODL（mg/L）?

Thefollowinginformationshouldbeuseful.

Priortodischargeofthewastewater,theriverhasaflowof50MGD（2.19m3/s）,aDOof7.0mg/L,aBODLof3.0mg/L,andatemperatureof23.5oC.Thewastewaterhasaflowof2MGD（0.0876m3/s）,aDOof0.5mg/L,atemperatureof36.5oC,andanuntreatedBODLof1,000mg/L.Ifneeded,assumek=0.24d-1,kd=0.32d-1,andkr=0.40d-1,allat20oC.Also,ifneeded,assumethevelocityoftheriverafterwastewaterdischargeis0.13m/s（7mile/d）.YES;881mg/L

8.（4pts）

A5-dayBODtestistobeconductedonaleachatesample.Twenty（20）mLofleachateareaddedto280mLofBODdilutionwater.After5daysincubationinthedark,measurementsindicatedthat4mg/Lofdissolvedoxygenhadbeenconsumed.

（a）AtwhattemperatureistheBOD5testusuallyconducted?

（b）WhatistheBOD5oftheleachate?

60mg/L

9.（10pts）

Anindustrialsmelterisbeingdesigned.Itwillhaveaneffectivestackheightof125mandisexpectedtoemit130g/sofparticulatematter（PM）.Theaverageannualwindspeedisexpectedtobeabout3.5m/s.

（a）Foranovercastdayandagroundtemperatureof20oC,andassumingnoinversion,calculatetheconcentrationofPM（ing/m3）expectedatgroundlevel10kmdirectlydownwindfromthesmelter.

（b）Foranovercastdayandagroundtemperatureof20oC,andassumingthereisaninversionwithamaximummixingheightof425m,calculatetheconcentrationofPM（ing/m3）expectedatgroundlevel10kmdirectlydownwindfromthesmelter.

（a）1.07x10-4g/m3;（b）1.07x10-4g/m3

10.（5pts）

TheStateDNRmandatesthattheminimumallowableseepagerateforlandfilllinersistobe1gal/ac-d（=9.4x10-7m/d）.Apreliminarydesignofalinersystemrecommendsageomembranewithathicknessof0.3mm（=3x10-4m）.Thislinerhasareportedpermeability（hydraulicconductivity）of10-13cm/s（=10-15m/s=8.64x10-11m/d）andaporosityof0.30.Themaximumleachatelevelabovethislinerisexpectedtobe1m.AssumingDarcy’slawapplies,willthislinermeetthestaterequirementsforallowableseepagerate?

Showallcalculationsnecessarytojustifyyouranswer–ayesornowithoutthesecalculationswillreceivenocredit.NO（9.6x10-7m/d）

11.（1pteachblank=5pts）

（a）Ofallthegreenhousegasseswediscussedinclass,itiscurrentlybelievedthatisthelargestcontributortothegreenhouseeffect.

（b）InclasswelistedthesixcriteriapollutantsthatarelistedintheNAAQS.List3ofthem:

,.

（c）TrueorFalse.ThelargestcontributorbyweighttoMSWintheU.S.isplastics.

53:

050FinalExam

POTENITALLYUSEFULFORMULAEANDOTHERINFORMATION

1m3=1,000L1kg=1,000g=106mg=109gR=0.0821

1d=86,400s

T（oC）Cs（mg/L）T（oC）Cs（mg/L）

413.48228.83

512.80238.58

1011.33248.53

1510.15258.38

169.95268.22

179.74278.07

189.54287.92

199.35297.77

209.17307.63

218.99357.07

Atom/Ion/MoleculeMWEW

Ca3（PO4）231051.67

CaCO310050

Ca2+4020

Mg2+24.312.15

CO24422

H2CO36231

HCO3-6161

CO32-6030

H3PO498-

H2PO4-97-

HPO42-96-

PO43-95-

O16-

H1-

N14-

P31-

S32-

pV=nRT

=-k

=-kC

=-kC2

CDI=C

=-kLBODt=BODL（1–e-kt）

=kr（Cs–C）=krD

Lt=

Dt=

tc=

=

Dc=

kd=k+

kd,T=kd,20（1.135）T-20or=kd,20（1.056）T-20

kr=

kr,T=kr,20（1.024）T-20

v=K

R=1+

KocfocKoc=0.63Kow

（x,y,0,H）=

=

sz=0.47（L–H）H=h+HH=

H2OH++OH-pKw=14（at25oC）

CO2（aq）↔CO2（g）KH=31.6L-atm/mol（at25oC）

sz=cxd+fsy=ax0.894