24993385 Water Waste Water Treatment

8/3/2019 24993385 Water Waste Water Treatment

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Water & Wastewater TreatmentWater & Wastewater Treatment

Objectives:Objectives:

Define primary, secondary, and tertiary treatmentDefine primary, secondary, and tertiary treatment

Define BODDefine BOD Describe the activated sludge processDescribe the activated sludge process

Setup and solve a mass balance for an activatedSetup and solve a mass balance for an activatedsludge systemsludge system


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SettlingSettling

Settling velocity:Settling velocity:

Percent of particles removed: (1Percent of particles removed: (1--CCssss/C/Css,oss,o) x 100%) x 100% Where,Where,

ReviewReview

Sorption:Sorption:

KKdd=C=Css/C/CLL

CCTT=(1+K=(1+KddCCssss)C)CLL

Fraction sorbed vs. fraction remaining in waterFraction sorbed vs. fraction remaining in water

218

dg

v wss VV

Q

!

Q

AvC

C

soss

ss

!

1

1

,


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WellWell--Mixed Settling TankMixed Settling Tank

Q

AvC

C

soss

ss

!

1

1

,

Q, Css,o Q, CssCssvs V

Suspended solids remaining: Define the Overflow Rate:

A

Q

~ 20 100 m/day in treatment plants


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Wastewater TreatmentWastewater Treatment

POTWPOTW Publicly Owned Treatment WorksPublicly Owned Treatment Works

0.40.4 0.6 m0.6 m33/person/day/person/day

15 million people in Los Angeles15 million people in Los Angeles

7.5 x 107.5 x 1066

mm33

/day/dayor 2000 MGD (million gallons per day)or 2000 MGD (million gallons per day)

HyperionHyperion 450 MGD450 MGD

Clean Water Act (CWA)Clean Water Act (CWA) 19771977 Set effluentSet effluent

(what is released by treatment plants into the(what is released by treatment plants into theenvironment) standardsenvironment) standards


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Stages ofWater TreatmentStages ofWater Treatment

PrimaryPrimary

ContaminantsContaminants (60% of solids and 35% of BOD removed)(60% of solids and 35% of BOD removed)

Oil & GreaseOil & Grease

Total Suspended Solids (CTotal Suspended Solids (Cssss or TSS)or TSS) 60% Removed60% Removed PathogensPathogens

BODBOD 35% removed35% removed

ProcessesProcesses

ScreensScreens

Grit SettlingGrit Settling

Scum FlotationScum Flotation

Primary SettlingPrimary Settling


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SecondarySecondary

ContaminantsContaminants

BODBOD 90% Removed90% Removed

TSSTSS 90% Removed90% Removed

ProcessesProcesses

Trickling FilterTrickling Filter rotating diskrotating disk

Activated SludgeActivated Sludge Suspended and mixedSuspended and mixed Oxidation pondsOxidation ponds lagoonslagoons

(promote contact between microbes and contaminants)(promote contact between microbes and contaminants)

Stages (continued)Stages (continued)


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Stages (continued)Stages (continued)

TertiaryTertiary

ContaminantsContaminants

NutrientsNutrients

Dissolved solids (e.g., salt, other ions, etc.)Dissolved solids (e.g., salt, other ions, etc.)

ProcessesProcesses

DenitrificationDenitrification bacteriabacteria

Phosphorus removalPhosphorus removal precipitationprecipitation Other chemicalsOther chemicals adsorption and precipitationadsorption and precipitation


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Primary Sludge (contd)Primary Sludge (contd)


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Primary SludgePrimary Sludge


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Primary SludgePrimary Sludge

(contd)(contd)

Given:Given: Q = 4000 mQ = 4000 m33/d/d

CCss,oss,o = 200 mg/L and C= 200 mg/L and Cssss = 100 mg/L= 100 mg/L

Sludge density = 0.05 kg/LSludge density = 0.05 kg/L

Overflow rate of 50 m/dOverflow rate of 50 m/d

FindFind

Population of town served by this unitPopulation of town served by this unit Sludge production rateSludge production rate

Area of settling tankArea of settling tank

Settling velocity of particlesSettling velocity of particles

CutCut--off size of particles (find the particle diameter corresponding to thisoff size of particles (find the particle diameter corresponding to thissettling velocity. Assumesettling velocity. Assume VV

ss

= 2600 kg/m= 2600 kg/m33. All particles larger than this. All particles larger than thissize will settle)size will settle)

Q, Css,o Q, Css

rateproductionsludgems !


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Activated SludgeActivated Sludge


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Activated Sludge ComponentsActivated Sludge Components


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Activated Sludge ComponentsActivated Sludge Components


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Activated Sludge (contd)Activated Sludge (contd)


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Activated Sludge NomenclatureActivated Sludge Nomenclature

Q, So, Xo

Q+QR,

S, XQ-Qs, S

Qs+QR, Xs

Qs, Xs

QR, Xs

S stands for conc.of substrate (organic matter, waste, etc.) or

BOD


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Activated Sludge NomenclatureActivated Sludge Nomenclature

(co

ntd)(co

ntd)Q, So, Xo Q+QR, S, X ~Q, S

Qs+QR, Xs

Qs, XsQR, Xs

Assumptions: Effluent bacteria concentration is 0 Concentration of substrate or BOD in sludge is 0 Sludge flowrate (Q

s

) is much smaller than Q

Q, V


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Decay ofBOD and growth ofDecay ofBOD and growth of

organismsorganisms

Substrate or BOD (S) decays with rate k:Substrate or BOD (S) decays with rate k:

Microbes (X) grow at rateMicrobes (X) grow at rate QQ::

kS

dt

dS!

Xdt

dXQ!


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Activated Sludge EquationsActivated Sludge Equations

The following equations are derived fromThe following equations are derived from

conducting mass balances over:conducting mass balances over:

The entire systemThe entire systemThe aeration tankThe aeration tank

The sedimentation tankThe sedimentation tank

Any good book on wastewater engineering willAny good book on wastewater engineering willhave the derivations if you are curious!have the derivations if you are curious!


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Activated Sludge EquationsActivated Sludge Equations

Biomass (X) balance over entire system:Biomass (X) balance over entire system:

Substrate (S) balance over entire system:Substrate (S) balance over entire system:

XVXQm sss Q!!

kSV

XV

consumedBOD

producedbiomassY

mXVSSYQ so

Q

Q

!!

!!


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More AS equationsMore AS equations

Mass balance over sedimentation tank:Mass balance over sedimentation tank:

Other equation(s)/rules of thumb:Other equation(s)/rules of thumb:

F/M = QSF/M = QSoo/XV/XV -- FoodFood--toto--microbe ratio: 0.3microbe ratio: 0.3 0.7 d0.7 d--11

QQRR~ 0.25~ 0.25 0.50 x Q0.50 x Q

X~

1000X~

1000 2000 mg/L2000 mg/L Problem types:Problem types:

Given Q, SGiven Q, Soo, and S (target concentration), and S (target concentration)

Find QFind QRR, Q, Qss, X,, X, QQ, V, Y, V, Y

sRR XQXVXQQ ! Q


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ExampleExample

Find QFind Qss,, QQ, V, Y, V, Y

Given:Given: Q = 1000 mQ = 1000 m33/d/d

SSoo = 150 mg/L= 150 mg/L

S = 15 mg/LS = 15 mg/L

QQRR= 240 m= 240 m33/d/d

F/M = 0.3 dF/M = 0.3 d--11 X = 2000 mg/LX = 2000 mg/L

XXss = 1% or 10,000 mg/L= 1% or 10,000 mg/L


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Definition ofBODDefinition ofBOD

Microorganisms (e.g., bacteria) are responsible for decomposingMicroorganisms (e.g., bacteria) are responsible for decomposingorganic waste. When organic matter such as dead plants, leaves,organic waste. When organic matter such as dead plants, leaves,grass clippings, manure, sewage, or even food waste is present ingrass clippings, manure, sewage, or even food waste is present ina water supply, the bacteria will begin the process of breakinga water supply, the bacteria will begin the process of breakingdown this waste. When this happens, much of the availabledown this waste. When this happens, much of the availabledissolved oxygen is consumed by aerobic bacteria, robbing otherdissolved oxygen is consumed by aerobic bacteria, robbing otheraquatic organisms of the oxygen they need to live. Biologicalaquatic organisms of the oxygen they need to live. BiologicalOxygen Demand (BOD) is a measure of the oxygen used byOxygen Demand (BOD) is a measure of the oxygen used bymicroorganisms to decompose this waste. If there is a largemicroorganisms to decompose this waste. If there is a largequantity of organic waste in the water supply, there will also be aquantity of organic waste in the water supply, there will also be a

lot of bacteria present working to decompose this waste. In thislot of bacteria present working to decompose this waste. In thiscase, the demand for oxygen will be high (due to all the bacteria)case, the demand for oxygen will be high (due to all the bacteria)so the BOD level will be high. As the waste is consumed orso the BOD level will be high. As the waste is consumed ordispersed through the water, BOD levels will begin to decline.dispersed through the water, BOD levels will begin to decline.

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24993385 Water Waste Water Treatment