Nitr if Ication

7/30/2019 Nitr if Ication

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7 Dissolved OxygenIntroduction

Oxygen Saturation

Biochemical Oxygen Demand

ReaerationStreeter-Phelps Equation

Nitrification

Sediment Oxygen Demand

Photosynthesis and Respiration

Expanded Streeter-Phelps EquationArtificial Re-aeration


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Dissolved Oxygen

Important for aquatic health DO standards typically 5 to 6 mg/L

Redox chemistry

Affects release of chemicals bound tosediments

Anaerobic conditions => H2S


3/37

Oxygen Saturation

]})15.273/(101407.2

)15.273/(754.10107674.1[)15.273/(10621949.8

)15.273/(10243800.1)15.273/(10642308.6

)15.273/(10575701.1103934411.1exp{),(

23

2411

31027

52

++

++

+++

++=

Tx

TxSTx

TxTx

TxxSTcs

=

)1)(1(

)1)(/1(),(),,(

wv

wv

ssp

pppSTcpSTc

])15.273/(1016961.2)15.273/(108407.38575.11exp[ 253 ++= TxTxpwv

285 10436.610426.1000975.0 TxTx +=

Standard Methods (1995)


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Cs (T, S, p)T=0o 10 20 30

Effect of p (S=0)

p = 1 atm (z=0) 14.6 11.3 9.1 7.6

p = 0.89 (1000m) 12.9 19.9 8.0 6.7p = 0.79 (2000m) 11.4 8.8 7.1 5.9

Effect of S (p=0)

S = 0 PSU 14.6 11.3 9.1 7.7

S = 10 13.6 10.6 8.6 7.2

S = 35 11.4 9.0 7.4 6.2


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Processes affecting DO

BOD (-)

Re-aeration (+/-)

P(+)/R(-)

Inflow

(+/-)

SOD (-)


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Biochemical Oxygen DemandOrganic wastes are food formicroorganisms Oxygen consumed in process

Self-purification (bio-degradation) innatural waters

Biological stage of WWT

Other chemicals exert oxygen demand C2H6O2

NaHSO3


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Theoretical Oxygen Demand

43

3222 )2

3

2

3

2()

4

5

4

3

24(

POdH

cNHOHdca

nCOOdcba

nPNOHC dcban

+

++=+++

OHHNOONH 22232

3++=+ +

=+322 2

1NOONO

Carbonaceous BOD (CBOD)

Nitrogenous BOD (NBOD)

Issues

Different types of wastes Some not labile

Rates vary (nitrification)


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Practical Measures of Oxygen Demand

BOD Traditional water quality measure

Cumbersome and time-consuming

COD

Easy to measure

TOC State variable in WQ models


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Traditional BOD

Practical measure of O2debt How much DO would decrease due to

respiration of organic wastes

BOD Jar Test Observe the decline of DO over time (e.g.

5 days) Extrapolate to ultimate demand

Used for wastewater and natural waters


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BOD Jar TestPrecautions

No photosynthesis

Enough initial O2

Adequate dilution (WW) Enough microorganisms

Non toxic sample

Only carbonaceous BOD


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[DO]

time

y5 = BOD5

yu =

BODu

y(t)

0

0 5 days

)1(1tK

eLy

=15

5

1K

e

LL

=

2011 )20(

=TKK

047.1~;5.01.0~)20( 11 dK

In rivers

sdr KKK +=

hwK ss /=


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Other Measures of BOD

COD Easy to measure

Much quicker

TOC State variable in WQ models

Relationship to BOD (Metcalf & Eddy) BOD5/COD ~ 0.4 to 0.8

BOD5/TOC ~1.0 to 1.6


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Stream ReaerationWater side control

Flux F ~ DO deficit

Piston velocity [LT-1]

kL ~ kw

Reaeration rate [T-1]

Ka

= K2

= kw

/h

Theories

Stagnant Film

Surface Renewal

H

c

cszw

h F=kL(cs-c)

= zw


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Stream ReaerationStagnant Film

kL = D/zw

Surface Renewal

zw ~ (Dt)0.5 t ~ h2/Ez ~ h/u

zw ~ (Dh/u)0.5

kL ~ (Du/h)0.5

Ka ~ (Du/h3)0.5

H

c

F=kL(cs-c)

cszw

h


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Stream Reaeration Formulae

u in m/s, h in m, T=20o

5.1

5.093.3h

uKa = OConnor-Dobbins

(1958)

Churchill et

al. (1962

Owens &Gibbs

(1964)

67.1

0.5

h

uKa =

85.1

67.03.5

h

uKa =

Kovar, 19760.1

0.3

0.4

0.50.60.8

1

2Depth

(ft.)

3

456

8

10

20

30

40O'Connor

Owens

.05

0.5

5

10

105

Churchill

50100

1

50

0.2Velocity (ft./sec.)

0.3 0.4 0.6 0.8 1 2 3 4 5 6

0.1

Figure by MIT OCW.


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Other formulationsRate of Energy Dissipation (Tsivoglou

& Wallace, 1972)

Melching and Flores (1999)

uSuL

LSTH ==

/

Pool and Riffle Reaeration Coefficient

Ka

CV

Q < 0.56 517(uS)0.524Q-0.242 0.61

Q > 0.56 596(uS)0.528Q-0.136 0.44

Channel Control

Q < 0.56 88(uS)0.313H-0.353 0.59

Q > 0.56 142(uS)0.333H-0.66W-

0.243

0.60


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1-D Analysis

(Streeter-Phelps, 1925)

Continuity

lqAu

xt

A=

+

)(

Mass Transport

)()()()(eiL rrA

x

cAE

xAuc

xAc

t++

=

+


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BOD (c = L)

LKr ri =ALqre /ll=

=x

xu

dx

0)(

A

LLqLK

dx

dLu r

)( += ll

)( LLLKd

dLr

+=l

[ ] { }])(exp[1)(

)(exp)(

+

+++= r

r

ro KK

LKLL l


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DO (c = c)LKr di =

)(/ ccKAcqr sae += ll

A

ccqccKLK

dx

dcu sad

)()(

++= ll

)()( ccccKLKd

dcsar ++= l

ccs =

]})(exp[])({exp[

)()(

]})(exp[1{))((

])(exp[)(

++

+

+

+++

++=

ar

r

o

ra

d

a

ar

d

ao

KvK

K

LL

KK

K

vKvKvK

LKK

l

l


20/37

Streeter-Phelps-additional comments

cmin

and xmin

can be calculatedanalytically

Multiple sources handled by

superposition or re-initialization atstream confluences

Procedures for anoxic conditions

Neglect of longitudinal dispersion?

Additional terms


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Nitrification

(2)(32/14) = 4.5743

3222 )

2

3

2

3

2

()

4

5

4

3

24

(

POdH

cNHOHdca

nCOOdcba

nPNOHC dcban

+

++=+++

OHHNOONH 22232

3++=+ +

=+ 3222

1NOONO (0.5)(32/14) = 1.14

Theoretical (upper bound) NBOD

NNONNHNOrgNBOD ++= 23 14.1)(57.4

TKN = total Kjeldalh nitrogenTKNNBOD 57.4


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[DO]

CBOD

NBOD

0

time0

Time scale for NBOD ~ 10 days => often insignificant in rivers

If important, separate CBOD & NBOD analyses required

May be better to include nitrogen species as state variables


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Sediment Oxygen Demand (SOD)

BOD in sediments

Significant downstream from outfalls orfollowing algal blooms

SB = 0.1 to 1 g/m2-d

re = SB/h

Oth order process

0.1 to 1 mg/L-d (h = 1 m)


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SOD (contd)Measured

in situwith benthic flux chambers

in lab with core

Calculated from organic carbon contentof settled solids

Calibrated from oxygen modelComplication: extraneous sources


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Benthic Flux Chambers


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Zebra Mussels

Algal Photosynthesis and


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Algal Photosynthesis and

Respiration

Photosynthesis (primary production) =>fixation of CO2 by autotrophic bacteria

Reverse is respiration

6CO2 + 6H2O C6H12O6 + 6O2


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P/R (contd)Limitations on primary production:

Light

Temperature

Nutrients

Time and space dependent

Diurnal variation Depth variation


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P(t)

Pm

Pa

24 hf0 t

ma Pf

P24

2= f = photoperiod (hrs)


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EPA (1985)

Curve A

Curve B

Wyman Creek, Calif

August 6, 1962

Average 10.1 MG/L

River Ivel, England

May 31, 1959

Average 10.4 MG/L

7

8

9

10

11

12

13

0600 06000900 1200N 1500 1800 2100 2400 0300

Hours

DissolvedO

xygenMG/L

Figure by MIT OCW.


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Estimation of P/RIn situ measurements w/ Light & DarkBottles

LKt

cc

R ddark

to

= mg/L-d; L = ultimate

BOD of filtered sample

dark

ot

light

ot

t

cc

t

cc

tP

=)(

P(t) is averaged over time t. t = 24 hrs => Pa;

t< 24 h => fit to diurnal variation using f


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Pm

t24 hf

Pa

0


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Estimation of P/R (contd)

Calibrate to observed diurnal variationin P(t) using estimated Ka

Delta Method (Chapra and DiToro, 1979)

Correlate with chlorophyll-a

aChlP = 25.0

aChlR = 025.0


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Expanded Streeter-Phelps Eqs*

h

RP

h

S

ccccKLKLKd

dc

u

B

saNNr

)(

)()(

+++=

l

CBOD NBOD* Reaeration Lat Inflow SOD P/R

[ ] { }])(exp[1)()(exp)(

+

+++=

rr

ro KK

L

KLL

l

])(exp[)( vKLL NNoN +=


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Expanded S-P (contd)

{ }

{ }

{ }

{ })])(exp[1)(

)/(

])(exp[])(exp[)(

])(exp[1))((

])(exp[])(exp[)(

])(exp[

++

++

+

++++

++

+

++=

a

a

B

aN

Na

NoN

a

ar

d

ar

r

o

ra

d

ao

KK

HSRP

KKKK

LK

KKK

LK

KKK

LL

KK

K

K

l

l


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Expanded S-P (contd)Lateral BOD sources w/o significant inflow

ALqLrd

ll= 0= ux/=

[ ]

{ }

[ ] [ ]

[ ])/exp(1

)/exp()/exp()(

)/exp(1

)/exp()/exp()(

)/exp()/exp()/exp(

uxK

K

HSRP

uxKuxKKKK

LKuxKKKLK

uxKuxKKK

LK

uxKuxKKK

LKuxK

a

a

B

ar

rra

rdd

a

ar

rdd

aN

Na

NoN

arra

od

ao

+

+

+=


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Artificial ReaerationOpen water bodies (direct transfer,turnover, fountains)

Hydropower stations (inject to turbine

intake, downstream aeration)

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