Operation of Activated Sludge Nitrification · 2020-06-24 · •The Activated Sludge Process is a SYSTEM ... NITRIFICATION MUST PRECEDE DENITRIFICATION! 21 22. 6/24/2020 12 Nitrification

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Operation of Activated Sludge Nitrification

Paul Dombrowski, Woodard & Curran, Inc.Spencer Snowling, Hydromantis, Inc.

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How to Participate Today

• Audio Modes

• Listen using Mic & Speakers

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• Submit your questions using the Questions pane.

• A recording will be availablefor replay shortly after thiswebcast.

Paul Dombrowski, PE, BCEE, F.WEF, Grade 6 Operator (MA)

Chief TechnologistWoodard & Curran, Inc.

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Spencer Snowling, Ph.D, P.Eng

V.P., Product Development

Hydromantis Environmental Software Solutions, Inc.

Webinar Agenda

• Introductions

• Activated Sludge Overview

• Simulator Description and Overview

• Nitrification Theory and Examples

• Simulator Examples

• Hydromantis Project

• Questions

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Activated Sludge Overview

Activated Sludge Operation

• The Activated Sludge Process is a SYSTEM Aeration Tank Secondary Clarifier RAS & WAS Pumps Aeration Equipment

• Secondary Treatment (BOD, TSS) Aeration Tanks - Convert soluble, colloidal and remaining suspended BOD

into biomass that can be removed by settling Secondary Clarifiers – Flocculate, settle and compact solids to provide

effluent low in TSS KEY – Create a biomass that flocculates well and settles rapidly

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Key Activated Sludge Relationships

Solids Retention Time (days)

“Average time any particle remains in Reactor Tanks”

SRT = lbs MLSS in Reactor Tankslbs/d WAS (Xw) + lbs/d Effluent TSS (Xe)

What parts of this can an operator control?

Key Activated Sludge Relationships

Aerobic Solids Retention Time (days)

“Average time any particle remains in Aeration Tanks”

Aerobic SRT = lbs MLSS in Aeration Tanklbs/d WAS (Xw) + lbs/d Effluent TSS (Xe)

What parts of this can an operator control?

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Secondary Clarifier Impacts on BNR

Two Key Concepts:

• Effluent TSS contains nutrients

• Secondary clarifiers define allowable reactor MLSS High Aerobic SRT required for nitrification

As SRT increases for a given reactor volume, MLSS concentration must increase

As a result, allowable MLSS can limit SRT

Process Simulators

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Simulator Overview

• Model = Series of equations that defines a process or plant Model based on mass balances and biological conversions of

organics (COD), nitrogen, phosphorus and solids

• Simulator = Program that uses a process model to experiment with a plant configuration

• OpTool Overlay = Plant-specific layout that provides graphical interface for plant operational testing and training

GPS-X Process Simulator

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Process Simulator Layout

Nitrogen in the Environment

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Particulate Organic - N Ammonia - N Nitrite - N Nitrate - N

Total Kjeldahl Nitrogen NOX - N

Total Nitrogen

InorganicNitrogen

SolubleKjeldahlNitrogen

Total SolubleNitrogen

Soluble Organic - N

OrganicNitrogen

Forms of Nitrogen

Why Remove Nitrogen?

• Toxicity: Ammonia

• Oxygen Demand: Ammonia

• Groundwater Contamination: Nitrate

• Eutrophication: Total Nitrogen Long Island Sound

Narragansett Bay

Chesapeake Bay

San Francisco Bay

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Environmental Conditions

• Aerobic Free dissolved oxygen present

• Anoxic No free dissolved oxygen Nitrite and/or nitrate present

• Anaerobic No free dissolved oxygen No nitrite or nitrate

Biological Nitrogen Removal

• Assimilation Incorporation of nitrogen into cell mass, typically 5% of BOD

removed (7-10% of VSS formed)

• Ammonification Conversion of organic nitrogen into ammonia

• Nitrification Oxidation of ammonia to nitrite then nitrate

• Denitrification Reduction of nitrate to nitrogen gas

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Nitrification

Nitrification BasicsNH4

+-N + 2 O2 NO3--N + 2 H+ + H2O + Bacteria

Autotrophic Bacteria – Ammonia and Nitrite Oxidizing Bacteria (AOB and NOB)

Energy from Oxidation of NH4+-N

Carbon from HCO3- (BiCarbonate)

Aerobic Organisms – DO Sensitive (Require 4.6 lb/lb NH4-N) Low Growth Rate – Temperature Sensitive Produces Acid – Consumes Alkalinity (7.2 lb/lb NH4-N) pH Sensitive – Acclimation Sensitive to Toxics

NITRIFICATION DOES NOT RESULT IN A NET REMOVAL OF NITROGEN FROM WASTEWATER!

NITRIFICATION MUST PRECEDE DENITRIFICATION!

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Nitrification BasicsBasic Process Description :

Aerobic Conditions in Mixed Liquor

(Aerobic Zone)

New Cells

NO2-N NO3-NNH4-N

NOB

O2 + HCO3 O2 + HCO3

AOB

New Cells

DO Impact on Nitrification

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 1 2 3 4 5 6 7 8 9 10

DO Concentration (mg/L)

Nit

rifi

cati

on

Rat

e (%

of

max

)

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0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0 5 10 15 20 25 30

Wastewater Temperature (deg C)

Ma

xim

um

Nit

rifi

er

Sp

eci

fic

Gro

wth

Rat

e (m

g/m

g-d

)

Temperature Impacts on Nitrification

Activated Sludge Nitrification

• System Microbiology Can occur concurrent or following BOD removal

Heterotrophs grow faster than Nitrifiers,so must reduce overall system growth rate

Depends on Aerobic SRT

• Single Sludge Nitrification Continuous Flow Systems

Sequencing Batch Reactors (SBR)

Membrane Bioreactors (MBR)

• Separate Sludge Nitrification

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Separate Sludge Nitrification

RASPump

AerationTank(fully

aerobic)

Influent

SecondaryClarifier

BOD RemovalStage

SecondaryEffluent

SecondaryClarifier

RASPump

AerationTank(fully

aerobic)

NitrifiedEffluent

NitrificationStage

Single Sludge Nitrification

AerationTank

Influent

BOD Removal, Nitrification

RASPump

EffluentSecondaryClarifier

WasteSludge

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Min. Aerobic SRT for Nitrification

0

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4 6 8 10 12 14 16 18 20 22 24


Ae

rob

ic S

RT

(d

ay

s)

Assumptions:DO = 2 mg/LEff NH3-N = 1 mg/L

Kn = 1 mg/LpH > 7.2Source:1993 EPA Nitrogen Control Manual

Min. Aerobic SRT = y = 18.507e-0.098x

Steady State Nitrification – Temp.

0

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0 1 2 3 4 5 6 7 8

Aerobic SRT (days)

Eff

lue

nt

Am

mo

nia

-N (

mg

/L)

Aerobic SRT (days) @ 10C Aerobic SRT (days) @ 20C

Assumptions:DO = 2 mg/LEff NH3-N = 1 mg/L

Kn = 1 mg/L

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Process Simulator – ASRT Example

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Steady State Nitrification – D.O.

0

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10

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0 1 2 3 4 5 6 7 8 9 10 11 12

Efflu

ent A

mm

onia

-N (m

g/L)

Aerobic SRT (days)

Effluent Ammonia @ DO=3 mg/L



Effluent Ammonia @ DO=0.5 mg/L

Assumptions:Influent BOD = 220 mg/LInfluent TKN = 40 mg/L T = 15 deg CKn = 1 mg/L

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Process Simulator – DO Example

Aerobic SRT for Nitrification

0

2

4

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10

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Ae

rob

ic S

RT

(d

ays

)

Assumptions:DO = 2 mg/LEff NH3-N = 1 mg/LKn = 1 mg/LpH > 7.2Source:1993 EPA Nitrogen Control Manual

Operating Aerobic SRT @PDF = 2.0

Minimum Aerobic SRT for Nitrification

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Nitrification Performance – 4 Years

-10.0

-7.5

-5.0

-2.5

0.0

2.5

5.0

7.5

10.0

12.5

15.0

Jul-00 Jan-01 Jul-01 Jan-02 Jul-02 Jan-03 Jul-03 Jan-04

Aer

ob

ic S

RT

(d

ays)

0

5

10

15

20

25

30

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40

45

50

Eff

luen

t A

mm

on

ia C

on

c. (

mg

/L)

Calculated 7-Day Moving Avg. Min. Aerobic SRT (days) Actual Aerobic SRT (days)

Calculated 7-Day Moving Avg Aerobic SRT Goal (days) Eff NH3-N (mg/L)

Nitrification Performance – 2002

-10.0

-7.5

-5.0

-2.5

0.0

2.5

5.0

7.5

10.0

12.5

15.0

Sep-01 Nov-01 Dec-01 Feb-02 Apr-02 May-02 Jul-02 Sep-02 Oct-02 Dec-02

Aer

ob

ic S

RT

(d

ays)

0

5

10

15

20

25

30

35

40

45

50

Eff

luen

t A

mm

on

ia C

on

c. (

mg

/L)



.

.

.

.

Period when Actual Aerobic SRT lessthan SRT Goal but more than Minimum

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Nitrification Performance – 2003

-10.0

-7.5

-5.0

-2.5

0.0

2.5

5.0

7.5

10.0

12.5

15.0

Dec-02 Jan-03 Mar-03 May-03 Jun-03 Aug-03 Oct-03 Nov-03

Ae

rob

ic S

RT

(d

ays

)

0

5

10

15

20

25

30

35

40

45

50

Eff

lue

nt

Am

mo

nia

Co

nc

. (m

g/L

)



.

.

.

.

Period when Actual Aerobic SRT lessthan SRT Goal but more than Minimum

NitrificationRe-acclimation Period

Nitrite “Lock”• Nitrite-N is an intermediate product of nitrification

• Causes: Low aerobic SRT

Low pH

NOB toxicity

• Impacts: Chlorine demand (5 mg Cl per mg NO2-N)

Disinfection performance problems

Effluent toxicity

• Solutions

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Alkalinity Check

• Should maintain at least 50-75 mg/L Alkalinity in Effluent

• Effluent Alkalinity = Alkinf – Alknit + Alkdenit

• Alkalinity also consumed through Chemical P Removal

• Chemicals typically used to add Alkalinity: Sodium Hydroxide (NaOH) – aka Caustic Soda

Sodium Carbonate (Na2CO3) – aka Soda Ash

Sodium Bicarbonate (NaHCO3) – aka Baking Soda

Magnesium Hydroxide (Mg(OH)2) – aka Milk of Magnesia

Potassium Hydroxide (KOH) – aka Caustic Potash or Lye

Quicklime (CaO)

Evaluating and Improving Nitrification

UNDERSTAND THE LIMITING

FACTORS

BIOMASS OXYGEN

ALKALINITY/pH

Increase Aerobic SRT Increase DO Concentration

Add Alkalinity

SLUDGE PRODUCTION

Reduce Organic Loading to Reactors

Improve denitrification Chemical addition

Improve PC Performance

Chemical Addition

Increase MLSS Concentration Increase Aeration Volume Add Fixed Film Media

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Nitrification Case Study

Nitrification Case Study

• North Davis Sewer District, Syracuse, Utah

• 80 sq. miles, 200,000 pp.

• 34 MGD capacity

• Biological Nitrogen Removal

• Chemical Phosphorus Removal

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North Davis Sewer District (NDSD)

Influent Headworks

Primary Clarifiers

Biotowers and Trickling Filters

BioreactorsSecondary Clarifiers

ChlorinationSolids

Handling


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• Nitrification Study: Start from conditions

resulting in high effluent ammonia

What changes are required to get effluent ammonia to < 2.0 mgN/L?


• Nitrification Study: What are the conditions in

the activated sludge system (DO and SRT)?

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• Nitrification Study: How can we increase DO?

Increase Airflow


• Nitrification Study: How can we increase DO?

Increase Airflow

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• Nitrification Study: How can we increase SRT?

Decrease WAS


• Nitrification Study: How can we increase SRT?

Decrease WAS

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• Nitrification Study: ↑ DO, ↑ SRT = ↓ Ammonia

Questions?

Paul [email protected]

(860) 253-2665

Spencer [email protected]

(905) 522-0012

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Documents

Operation of Activated Sludge Nitrification · 2020-06-24 · •The Activated Sludge Process is a SYSTEM ... NITRIFICATION MUST PRECEDE DENITRIFICATION! 21 22. 6/24/2020 12 Nitrification