Operation of Activated Sludge Nitrification Paul Dombrowski, Woodard - - PDF document

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Operation of Activated Sludge Nitrification Paul Dombrowski, Woodard - - PDF document

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6/24/2020 1 Operation of Activated Sludge Nitrification Paul Dombrowski, Woodard & Curran, Inc. Spencer Snowling, Hydromantis, Inc. 2 1 6/24/2020 How to Participate Today Audio Modes Listen using Mic & Speakers Or,

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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

  • Or, select “Use

Telephone” and dial the conference (please remember long distance phone charges apply).

  • Submit your questions

using the Questions pane.

  • A recording will be

available for replay shortly after this webcast.

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

Chief Technologist Woodard & 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 Tanks lbs/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 Tank lbs/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
  • rganics (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 Inorganic Nitrogen Soluble Kjeldahl Nitrogen Total Soluble Nitrogen Soluble Organic - N Organic Nitrogen

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 Basics

NH4

+-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 Basics

Basic Process Description :

Aerobic Conditions in Mixed Liquor

(Aerobic Zone)

New Cells

NO2-N NO3-N NH4-N

NOB O2 + HCO3 O2 + HCO3 AOB

New Cells

DO Impact on Nitrification

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 1 2 3 4 5 6 7 8 9 10 DO Concentration (mg/L) Nitrification Rate (% of max)

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0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 5 10 15 20 25 30 Wastewater Temperature (deg C) Maximum Nitrifier Specific Growth Rate (mg/mg-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

RAS Pump Aeration Tank (fully aerobic) Influent Secondary Clarifier

BOD Removal Stage

Secondary Effluent Secondary Clarifier RAS Pump Aeration Tank (fully aerobic) Nitrified Effluent

Nitrification Stage

Single Sludge Nitrification

Aeration Tank Influent

BOD Removal, Nitrification

RAS Pump Effluent Secondary Clarifier Waste Sludge

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  • Min. Aerobic SRT for Nitrification

2 4 6 8 10 12 14 16 18 20 22 4 6 8 10 12 14 16 18 20 22 24 Wastewater Temperature (deg C) Aerobic SRT (days) Assumptions: DO = 2 mg/L Eff NH3-N = 1 mg/L Kn = 1 mg/L pH > 7.2 Source: 1993 EPA Nitrogen Control Manual

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

Steady State Nitrification – Temp.

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 1 2 3 4 5 6 7 8 Aerobic SRT (days) Effluent Ammonia-N (mg/L)

Aerobic SRT (days) @ 10C Aerobic SRT (days) @ 20C Assumptions: DO = 2 mg/L Eff 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.

5 10 15 20 25 30 35 1 2 3 4 5 6 7 8 9 10 11 12 Effluent Ammonia-N (mg/L) Aerobic SRT (days) Effluent Ammonia @ DO=3 mg/L Effluent Ammonia @ DO=2 mg/L Effluent Ammonia @ DO=1 mg/L Effluent Ammonia @ DO=0.5 mg/L

Assumptions: Influent BOD = 220 mg/L Influent TKN = 40 mg/L T = 15 deg C Kn = 1 mg/L

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Process Simulator – DO Example Aerobic SRT for Nitrification

2 4 6 8 10 12 14 16 18 20 22 4 6 8 10 12 14 16 18 20 22 24 Wastewater Temperature (deg C) Aerobic SRT (days) Assumptions: DO = 2 mg/L Eff NH3-N = 1 mg/L Kn = 1 mg/L pH > 7.2 Source: 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 Aerobic SRT (days) 5 10 15 20 25 30 35 40 45 50 Effluent Ammonia Conc. (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 Aerobic SRT (days) 5 10 15 20 25 30 35 40 45 50 Effluent Ammonia Conc. (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) . . . . Period when Actual Aerobic SRT less than 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 Aerobic SRT (days) 5 10 15 20 25 30 35 40 45 50 Effluent Ammonia Conc. (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) . . . . Period when Actual Aerobic SRT less than SRT Goal but more than Minimum Nitrification Re-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 Bioreactors Secondary Clarifiers Chlorination Solids Handling

North Davis Sewer District (NDSD)

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North Davis Sewer District (NDSD)

  • Nitrification Study:
  • Start from conditions

resulting in high effluent ammonia

  • What changes are required

to get effluent ammonia to < 2.0 mgN/L?

North Davis Sewer District (NDSD)

  • Nitrification Study:
  • What are the conditions in

the activated sludge system (DO and SRT)?

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North Davis Sewer District (NDSD)

  • Nitrification Study:
  • How can we increase DO?

Increase Airflow

North Davis Sewer District (NDSD)

  • Nitrification Study:
  • How can we increase DO?

Increase Airflow

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North Davis Sewer District (NDSD)

  • Nitrification Study:
  • How can we increase SRT?

Decrease WAS

North Davis Sewer District (NDSD)

  • Nitrification Study:
  • How can we increase SRT?

Decrease WAS

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North Davis Sewer District (NDSD)

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

Questions?

Paul Dombrowski pdombrowski@woodardcurran.com (860) 253-2665 Spencer Snowling Snowling@hydromantis.com (905) 522-0012

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