ae 98 civ b5 water supply and wastewater treatment may 2002

8/12/2019 AE 98 Civ B5 Water Supply and Wastewater Treatment May 2002

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98-Civ-BS (May 2002): WATER SUPPL Y AND W ASTEW A TER TREATMENT3 Hours Duration

NOTES:1 If doubt exists as to the interpretation of any question, the candidate is urged to submit with

the answer paper, a clear statementof any assumption(s)made.2. This is an open book exam although sufficient information is provided to answer all questionswithout additional referencematerial.3. Candidatesmay use one of two calculators, he Casio or Sharp approved models.4. There are five sections o this exam (parts A, B, C, D and E) with percentage weightings asindicated. All questionswithin each respective section are worth equal marks but may not beof equal difficulty .The following is a suggested ime allocation for the exam parts:

Part A: 15 minutesPart B: 15 minutesPart C: 45 minutesPart D: 60 minutesPart E: 45 minutes

5. The exam table of contents s as follows: Page(10% Weight) 2(20% Weight) 3

(25 % Weight) 4(25 % Weight) 6(20% Weight) 711

121313

Part A: General Knowledge -Water Quality and Treatment IPart B: General Knowledge -Water Quality and Treatment nPart C: Measurement and Mass Balance TheoryPart D: Numerical ProblemsPart E: Treatment Process DesignEquations and Useful Information .Table of Atomic Weights .Dissociation Constants at 25C .Inorganic carbon species as a function ofpH at 0.005 M TIC

6. Indicate what you are solving for in any intennediate steps to a solution.Neat well-annotated answerswill tend to collect more marks..

8. Clearly define your notation and method of approach.9. Clearly work through ideas, concepts and specify applied formulae before substituting in anynumbers.10. Do Q erase false starts", instead strike a line across he section of the page that still permitsthe work to be read and continue on.

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Part A: General Knowledge -Water Quality and Treatment I (10% Weight)In three short points indicate your understanding of any 4 out of the 10 terms listed below by:a. Defming the term (or acronym), andb. Indicating how it relates to or impacts on water/wastewater treatment design, monitoring

and/or operation.Be brief and to the point. Note that a lengthy verbose answer is not better and will work againstyou in time and marking -point form is preferred.

6. Trihalomethane. BODs2. Colifonns 7. Nitrate

8. Hardness. Flocculation9. voc. SVI10. GAC. pH

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Part c: Measurement and Mass Balance Theory (25 % Weight)Answer questions 1 and 2.I. The municipal biological wastewater treatment plant shown below (Figure I) consists ofunitprocesses abelled (a) to (i). The certificate of approval specifies effluent water quality

objectives of (I) BODs, (2) total suspendedsolids, (3) TKN (total Kjedal1 nitrogen), (4) TP(total phosphorus), and (5) coliform counts. Alum (A12(SO4)3 I8H20) is dosed at thelocation shown.a. With respect to the 5 water quality objectives indicate where and how the treatment plantreduces the levels of these parameters in the wastewater.b. What are the residual(s) that are being produced in treating the wastewater?

The unit process e) is not performing well. You suspect his"might involve unanticipateddenitrification within ( e . What would you measure o test whether or not your suspicionsare well founded?c.

Figure I. Activated sludge plant for domestic wastewater treatment.

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vss measurements an be used to make an assessment f the biomass levels in an activatedsludge treatment system. However, measurements f similar VSS levels may consist of quitedifferent levels of ~ microorganisms and Monod kinetics relate to these activemicroorganisms. Therefore VSS measurements Xv) from the aeration basin of an activatedsludge process should really be divided into active microorganisms (Xa) and inanimatevolatile suspended olids (Xu:

Xv =Xa +XiAssuming no influent VSS, the inanimate VSS (Xi) is produced as a result of endogenousdecay:

rj =(l- d)Xakdwhere

= specific production rate ofXj (mg VSS/L/d)rj= fraction of the active biomass that is biodegradable (typically -0.8)fd= endogenous decay rate (l/d).~

a. For the bioreactor system shown in Figure 2, and from mass balance consideration,determine the effect of increasing HRT on the fraction of active biomass in a VSSmeasurement i.e. find an expression or "XaIXy").How would this change of "XalXv" be reflected in measurements of specific oxygenuptake rate (SOUR) as HRT increased for this system?b.

Figure 2. A completely mixed bioreactor with influent flow (Q), influent biodegradable dissolved organicmatter (Si), effluent biodegradable dissolved organic matter (S), reactor biomass (Xv), reactor volume (V) andeffluent dissolved organic matter (S).

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250-'0 I

Ne-0000>cn~~=~rIJ'0.-- Q00

200

150

100

50o~

05 10 15 20Biosolids concentration X (g VSS/L) 25

Figure 5. Graph from experimental data and best-fitted trend line for the gravity flux (Kg VSS/m2-d) for thesettling characteristics of the activated sludge solids (g VSS/L) for problem 111-1.

2. Disinfection Unit ProcessDesign:A chlorination disinfection process is to be designed according to the schematic diagramrepresented n Figure 6. From the influent water supply, a breakpoint curve was generated(Figure 7). Further, an experiment of coliform survivability with chlorination was performed(Figure 8).For this disinfection process, a free chlorine residual of 0.25 mg/L is required. The supply waterflow rate is Q = 20 Lis and the plug flow reactor is just a Y2 illed 1.2 meter diameter sewer pipe.There is no chlorine in the water supply.

Select a chlorine dosage (CD) for a free residual chlorine level (CR) of 0.25 mg/L..b. What is the chlorine supply line concentration (Cs) necessary o achieve your requireddosage (CD) if the chlorine supply flow (q) is equal to 0.1 percent of the wastewater low

Q?c. What should be the liquid volume of the plug flow reactor for 99% coliform removal?d. What length of sewer pipe is required for the plug flow reactor?

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Figure 6. Schematic of the disinfection process, where: C = chlorine concentration, Cs = chlorine supplyconcentration, CD = chlorine dosage, CR = chlorine residual concentration, Q = wastewater flow (LIs), and q =chlorine supply flow (LIs).

Figure 7. An experimentally derived breakpoint chlorination curve for the water, showing chlorine residualsresulting from respective doses.

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Equations and Useful Information1 m3 = 103L 1 cm3 = 1 mL = 10-3LConversion factors

Generalized Reactor Mass Balance

Hydraulic Retention Time (HRT or e)( v= volume, Q = flow rat~)-Critical Settling Velocity(9-=- flow rate, A = surface area)-Solids Retention Time (SRT or ex)

N=CuSolids FluxJC = conc.,~~ velocity)

QX ~ NLAlarifier design(Q = clarifier influent flow, X clarifier influentsolids concentration, NL = limiting flux, A =surfacearea)_- -

~c. I

Ce

1 st Order Reaction Kinetics (r = -kC): = exp(-ke)Plug Flow

1Ci = ~ Completely MixedC 1- -=C. I

~ ) n Series of n CM Reactors1+-

rx =-Yrs -kdXiomass growth kinetic with endogenous decay:

Monod kineticsra =aKLa(f3Cs -0)as TransferkT = k e (T-20)

20 Arrhenius TemperatureRelationshipES = PIO.U = P6o1Pl0d d U 1.67

_9_0--=-1. )-

Grain size distribution

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Table of Atomic Weights~Elements by Name, Symbol, Atomic Number, and Atomic Weight(Atomic weights are given to four significant figures for elements below atomic number 104. SeeA~dix D.)

Atomictomic

Mercw'YMolybdenumN eod ymi umNeonNeptU11iumNickelNielsbohriumNiobiumNitrogenNobeliumOsmiumOxygenPalladiumPh(?8phorusPlatinumPlutoniumPoloniumPotassiumPraseodymiumPromethiumProtactiniumRadiumRadonRheniumRhodiumRubidiumRutheniumRutherfordiumSamariumScandiumSeaborgiumlSeleniumSiliconSilver .SodiumStrontiumSulfurTantalumTeChnetiumTelluriumTerbiumThalliumThoriumThuliumT1I11itaniumTungstenUraniumVanadiumXenon .YtterbiumYttrium.ZincZin:onium

ActiniumAluminumAmericiumAntimonyArgonArsenicAstatineBariumBerkeliumBeIylliumBismuthBoronBromineCadmiumCalciumCaIifomiumCarbonCeriumCesiumOUorlneO\romiumCobaltCoppex:CuriumDysprosiumEinsteiniumErbiumEuropiumFermiumF1uorineFranciumGadoliniumGalliumGermaniumGoldHafniumHahniumHassiumHeliumHolmiumHydrogenIndiumIodineIridiumIronKryptonLanthanumLawrenciumLeadU thi umLutetiumMagnesiumManganeseMeitneriumMendelevium

...

aNames or elements 104.105. and 107 to 109 have been endorsed by a committee or the American OJemical Society.The IUPAC recommends different names ror elements 104 to 108.'Proposed symbol and name

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Dissociation Constants at 25C

4.7H3COOH ~ H+ + CB3~O-1.8 X 10-'5.8 X 10-10.1.5 X 10-',4.3 x 10-74.7 x 10-11Strong7.2 X 10-106.75 X 10-::49.1 X 10-8

4.79.24.86.4

10.3--3

.9.13~27.0

NH3 + H1O ~ NH: + OH- .H3B~ ~ H+ + H1BO3CJH7COqfl ~ H~ + c,H7COO-H2CO: ~ H+ + IitO3HCO3 ~ H+ + cotHa ~ H+ + a-HCN ~H+ + CN- .HF ~ H++ F- ..H2S ~ H+ + HS~

AmmoniaBoric acidButyric acidCarbonic acid

Hydrochloric acidHydrocyanic addHydrofluoric acidHydrosulfuric acid: (

.(hydrogen sUlfide) 12.97.5

-1.03.29

--79.9.2.17.2

12.3

HS- ~ H+ + S2-HOCl~:H+ + oa-HNO3 ~ H+ + NO3HN~ ~ H+ + NOiHaO4 ~ H+ + aO4~H,OH ~ H+ + ~H,O-H3PO4 ~ H+ + H2PO4H2PO4 ~ H+ + In>>O1-HPO1- ~ H+ + p9tKOH ~ K+ + ol:l-

AnalysesToxicityFluoridationOdor, corrosion,anaerobic digestion.

toxicityDisinfectionNitrification, analysesNitrificationAnalysesTastes, odorsBuffer, nutrient

1.3 X 10-132.9 X .10-10.105.1. x ~o~.Strong1..2 x 10-17.5 X 10-36.2 x 10-84.8 X 10-13Strong (base)

Hypochlorous acidNitric acidNitrous acidPerchloric acid' .PhenolPhospboricacid

Ana1ys~PotassiumhydroxidePropionic acid

Sodium hydroxideSulfuric acid

~HjCOOH ~ H.. + ~H5COO:: .NaOH ~ Na.. + OH-H2504 ~ H.. + HSO.HS04 ~ H.. + 501-HzSOJ ~ H+ + H503HSOj" ~ H.. + 50J-

4.9 .Anaerobic digestionAnalyses, neutralizationCoagulation,pHConqol, analysesDechlorination

--31.91.87.2

1.3:>< 10-$ -Strong (base)Strong'1.2 X 10-21.7 X 10-26.3 X 10-8

.Sulfurous acid

Inorganic carbon species as a function of pH at 0.005 M TIC

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ae 98 civ b5 water supply and wastewater treatment may 2002

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