(Chapra, L22 & L23) David Reckhow CEE 577 #18 1 Nitrogen - - PowerPoint PPT Presentation

Lecture #18 Streeter-Phelps: Distributed Sources & Nitrogen

(Chapra, L22 & L23)

David Reckhow CEE 577 #18 1

Print version

Updated: 30 October 2017

Nitrogen (Chapra L23)

 Nitrification/Denitrification

 nitrification: oxygen consuming  denitrification: anaerobic, form N2

 Eutrophication

 stimulates plant growth

 Nitrate pollution

 from fertilizers and nitrification

 Ammonia toxicity (NH3 form)

David Reckhow CEE 577 #18 2

Nitrogen Cycle

David Reckhow CEE 577 #18 3

Atmospheric N Organic N (plants) Organic N (animals) N in sediments

• r soils

Aqueous N Decomposition

Nitrification/Denitrification

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Nitrification: will satisfy NBOD and NH3 toxicity

NH O NO H O H

Nitrosomonas 4 3 2 2 2 2

2

+ − +

+  →   + +

NO O NO

Nitrobacter 2 1 2 2 3 − −

+  →  

Can be combined with traditional activated sludge so that NBOD is removed along with CBOD; occurs naturally in surface waters

Denitrification: will remove nitrate, nutrient control

NO N CO H O

3 2 2 2 − +

→ ↑ + +

• rganic

Requires an anaerobic environment

Modeling Nitrification

David Reckhow CEE 577 #18 5

( )

L L e S k e

N N o k t D n k t

n n

= + −

− −

1

Point Distributed

LN = 4.57*TKN

In-class problem I

 A poorly treated municipal wastewater is discharged into

Evergreen Brook at milepoint zero. In addition there is a continuous discharge of soluble BOD from a series of hog farms extending from milepoint zero to mile 25.

 The WWTP discharges sufficient BOD such that there is 12

mg/L BOD at the point of mixing, 30% of which is particulate

 The hog farms release 5 g-BOD/d for every foot of stream

length

 The stream can be considered to have a uniform depth of 4 ft,

a width of 22 ft and a rocky bottom. Velocity is 3 mi/d.

 Assume a BOD settling rate of 1.2 d-1

 What is the BOD concentration 10 miles downstream and

how much originates from each source (WWTP vs hog farm)?

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In-class problem II

 First determine distributed loading term  Next estimate deoxygenation rate  Then formulate BOD model

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( )(

)

d L mg ft ft H S A S S

L ft d ft g d c d d

− = = = =

−

. 2 22 4 5

3 . 28 1 ' ' '

3

1 434 . 434 .

405 . 8 4 3 . 8

− − −

=       =       = d H C kd

( )

( )

U x U x U x r r

e e e e k S e L L

t k r D t k

• 405

. 405 . 605 . 1

1 405 . 2 ) 7 . ( 12 ) 3 . ( 12 1

− − − − −

− + + = − + =

deoxygenation only, no settling

In-class problem II

David Reckhow CEE 577 #18 8

Distance Downstream (miles)

5 10 15 20 25

BOD (mg/L)

2 4 6 8 10 12 14 Dissolved Point Source Dissolved Distributed Source Particulate

 5.86 mg/L @10 mi

 2.19 mg/L from WWTP  3.67 mg/L from hog farms  Essentially all is dissolved

Full Equation

David Reckhow CEE 577 #18 9

( ) ( ) ( ) ( )

( )(

) ( )

( )(

)

t k t k n a n Nd n t k a n Nd n t k t k r a r d d t k a r d d t k a B t k t k n a No n t k t k r a

• d

t k

• a

n a a r a a a n a r a

e e k k k S k e k k S k e e k k k S k e k k S k e k H S R P e e k k L k e e k k L k e D D

− − − − − − − − − − − −

− − − − + − − − − + −       + + − + − − + − − + = 1 1 1

'

Point NBOD Distributed NBOD

Sample Problem (T&M, pg.309)

 Problem

 Determine the maximum allowable ultimate oxygen

demand (UOD) in the effluent entering the stream if the DO concentration is to equal or exceed 5 mg/L. Assume the effluent DO is equal to the stream’s DO saturation concentration.

David Reckhow CEE 577 #18 10

Qe = 4 MGD CBOD5 = 30 mg/L, f=2.0 NH3-N = 10 mg/L Qu = 20 cfs cu = cs Lu = Nu = 0 ka = 0.80/d @ 20oC kr=kd= 0.40/d @ 28oC kN = 0.40/d @ 28oC

Problem (cont.)

 Analysis of existing conditions

 Loading

 BOD and NBOD may be treated as one UOD load since the

decay rates are the same in the stream. Assume only the ammonia is significant in the NBOD.

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( )

L mg x x N NH x fxCBOD L mg UOD / 7 . 105 10 57 . 4 30 . 2 57 . 4 ) / (

3 5

= + = − + =

d lb x MGDx UOD W

L mg

/ 3530 34 . 8 7 . 105 4 ) ( = = ( ) ( )

L mg e u

• cfs

cfs d lb Q Q UOD W L . 25 4 . 5 548 . 1 4 20 / 3530 ) ( = + = + =

Problem (cont.)

 Adjust Reaction rates to ambient temp.  Determine tcrit

David Reckhow CEE 577 #18 12

( )

C d x C k k

• T
• a

a

28 @ 97 . 024 . 1 8 . ) 20 (

1 ) 20 28 ( 20 − − −

= = = θ

( )

d

• 1

L k k k D k k k

• k

1 = t

• d

r a

• r

a r a crit

55 . 1 . 25 40 . 40 . 97 . ( 1 40 . 97 . ln 40 . 97 . ( 1 ln =               − − =               − −

Problem (cont.)

 Then get xcrit  And cs is:

 accounting for temp. & altitude

 Finally the cmin is:

David Reckhow CEE 577 #18 13

( )

mi d fps Ut x

fps mpd

7 . 12 55 . 1 5 .

4 . 16

= = =

L mg t k a d

• s

e e k k L c c

crit r

64 . 97 . 40 . . 25 19 . 6

) 55 . 1 ( 40 . min

= − = − =

− −

L mg s

c 19 . 6 =

Problem (end)

 Determine allowable load, if WQC require 5.0

mg/L minimum D.O.

 Recognize that the loading:deficit relationship is

linear

 so determine allowable L

David Reckhow CEE 577 #18 14

crit rt

k a d

• s

crit

e k k L c c D

−

= − ≡

min

Also, tcrit is independent of L when Do=0

L mg crit

• allowable

crit allowable

• allowable
• allowable

crit

• crit

D L D L L D L D 23 55 . 5 ) 7 . 105 ( 19 . 1

) ( ) ( ) ( ) (

= = = =

Additional notes on WLA

 Selecting a model

 number of dimensions

 usually 1, major gradients are longitudinal, very minor

gradients in lateral and vertical directions

 sometimes 2, deep rivers or river-run impoundments; use

should be justified

 never 3, except research and a few extraordinary cases

David Reckhow CEE 577 #18 15

Not from Chapra

Additional notes on WLA (cont.)

 Loads, sources & sinks

 Categorize

 category I - major sources controlling water quality

 thorough data collection - temporal variation

 category II - background sources

 small to moderate data collection

 necessary data

 long-term BOD,with nitrification inhibition  analysis of all forms of nitrogen

 org-N, NH3, NO2, NO3

David Reckhow CEE 577 #18 16

Additional notes on WLA (cont.)

 Time scale

 steady state  quasi-steady state

 const. loads, constant Q, diurnal DO variations due to

photosynthesis

 const. loads, variable Q  variable loads, constant

Q

 others

 Fully time-variable analysis

David Reckhow CEE 577 #18 17

Additional notes on WLA (cont.)

 Design Conditions

 7Q10 - summer

 generally endorsed by USEPA

 Spring Floods - large event

 storm intensity, sequences, recessional hydrograph

 Ice cover - winter

 Spatial Extent

 well into the zone of recovery

David Reckhow CEE 577 #18 18

Additional notes on WLA (cont.)

 Dispersion (is it significant?)

 calculate E

 from slope  from dye studies

 calculate dimensionless estuary #  use Chapra’s criteria

 n<0.1, advection predominates  n>10, diffusion predominates

 or calculate reaeration/deoxygenation ratio & use

O’Connor figure

David Reckhow CEE 577 #18 19

E x UB HU =

−

34 10 5

2

.

*

U gHS

* =

mi2/d ft ft/s ft

n k E U

d

=

2

φ = k k

a d



Figure prepared by O’Connor



From: Technical Guidance Manual for Performing Waste Load Allocations: Book II, Chapter 1

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Full Equation

David Reckhow CEE 577 #18 21

( ) ( ) ( ) ( )

( )(

) ( )

( )(

)

t k t k n a n Nd n t k a n Nd n t k t k r a r d d t k a r d d t k a B t k t k n a No n t k t k r a

• d

t k

• a

n a a r a a a n a r a

e e k k k S k e k k S k e e k k k S k e k k S k e k H S R P e e k k L k e e k k L k e D D

− − − − − − − − − − − −

− − − − + − − − − + −       + + − + − − + − − + = 1 1 1

'

Point NBOD Distributed NBOD

Additional notes on WLA (cont.)

 Nitrogen modeling

 NBOD

 measure and model TKN only

 all 4 major species

 org-N, NH3, NO2, and NO3  requires separate analysis of loadings, rate coefficients, etc.

David Reckhow CEE 577 #18 22

General Model Kinetics

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Dissolved Oxygen CBOD

K1 K3

Atmosphere

K2

NBOD

KN1

SOD

K4

General Model Kinetics with N species

David Reckhow CEE 577 #18 24

Dissolved Oxygen CBOD

K1 K3

Atmosphere

K2

Organic N

β3

SOD

K4

NH3 NO2 NO3

β

1

β2 α β

5 1

σ4 σ3 α β

6 2

Additional notes on WLA (cont.)

 Algal modeling

 Level I

 measure P-R: diurnal swings in D.O.

 Level II

 measure chlorophyll a, light, light extinction, nutrients

“in-situ”

 calculate P-R

 Level III

 assess nutrient loadings, light extinction  model nutrient conc., chlorophyll a, P-R

David Reckhow CEE 577 #18 25

General Model Kinetics with algae

David Reckhow CEE 577 #21 26

Dissolved Oxygen CBOD

K1 K3

Atmosphere

K2

Organic N

β3

SOD

K4

NH3 NO2 NO3

β

1

β2 α β

5 1

σ4 σ3

(Ks) (Ka) (Kd) Chlorophyll a

(Algae)

Org-P Diss-P

α µ

1 F

α µ

1

1 ( ) − F

α µ

1

α ρ

1

α ρ

2

α µ

2

α µ

3

α ρ

4

β4

σ5 σ2

σ1

2 6β

α

 To next lecture

David Reckhow CEE 577 #18 27

 Ohio River

David Reckhow CEE 370 L#20 28