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7/7/2020 Operation of Activated Sludge Denitrification and Total Nitrogen Removal Systems Paul Dombrowski, Woodard & Curran, Inc. Spencer Snowling, Hydromantis, Inc. 1 How to Participate Today Audio Modes Listen using Mic &

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Operation of Activated Sludge Denitrification and Total Nitrogen Removal Systems

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

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

Chief Technologist Woodard & Curran, Inc.

Spencer Snowling, Ph.D, P.Eng

V.P ., Product Development Hydromantis Environmental Software Solutions, Inc.

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Webinar Agenda

  • Introductions
  • Activated Sludge and Nitrification

Overview

  • Simulator Description and Overview
  • Denitrification Fundamentals
  • Simulator Examples
  • Hydromantis Case Study
  • Questions

Activated Sludge and Nitrification Overview

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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

Key Activated Sludge Relationships

Mean Cell Residence Time (days) (from WEF WW Treatment Fundamentals)

“Average time any particle remains in Biological System” MCRT = lbs MLSS in Reactor Tanks + in Sec. Clarifiers lbs/d WAS (Xw) + lbs/d Effluent TSS (Xe)

What parts of this can an operator control?

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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 part of the SRT is excluded from the Aerobic SRT? THE ANOXIC AND ANAEROBIC ZONE MLSS INVENTORY

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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

HOW DOES REACTOR SRT AND MLSS CONC. IMPACT DENITE? HIGHER SRT RESULTS IN A HIGHER RATE OF ENDOGENOUS RESPIRATION (O2 and NOx DEMAND)

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 and NO2-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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Process Simulators 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 SimuWorks Overlay = Plant-specific layout that

provides graphical interface for plant operational testing and training

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GPS-X Process Simulator Process Simulator Layout

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Nitrogen in the Environment

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

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Why Remove Nitrogen?

  • Toxicity: Ammonia
  • Oxygen Demand: Ammonia
  • Groundwater Contamination: Nitrate
  • Eutrophication: Total Nitrogen
  • Long Island Sound
  • Narragansett Bay
  • Chesapeake Bay
  • San Francisco Bay

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

NITRIFICATION DENITRIFICATION

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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

Denitrification

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Denitrification Basics

2 NO3

  • -N + 12 H+ + 2.9 BOD N2 + 6 H2O + Bacteria

Reduction of nitrate to nitrogen gas Heterotrophic Bacteria – “BOD Removers”

  • Energy from Oxidation of Organic Carbon
  • Recovers Oxygen – (2.9 lbs O2 / lb NO3-N)
  • Anoxic Conditions Req’d – No or Low DO
  • Consumes Acid – Produces Alkalinity (3.6 lb CaCO3 / lb NO3-N)
  • Mixing Req’d - Maintain Complete Solids Suspension without adding DO

DENITRIFICATION MUST FOLLOW NITRIFICATION! DENITRIFICATION IS NECESSARY TO ACHIEVE TOTAL NITROGEN REMOVAL!

DO Impact on Denitrification

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.5 1 1.5 2 2.5 3 Dissolved Oxygen Concentration (mg/L) Denitrification Rate (% of Max)

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Factors Impacting Denitrification

Nitrification: Aerobic Conditions in Mixed Liquor

(Aerobic Zone)

NO2-N NO3-N NH3-N

NOB O2 + HCO3 O2 + HCO3 AOB

New Cells

CARBON SOURCE:

Raw Wastewater Endogenous Respiration Supplemental Carbon

Anoxic Conditions in Mixed Liquor

(Anoxic & Post Anoxic Zones)

N2(g)

cBOD

Denitrifying Biomass

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Factors Impacting Denitrification

CARBON SOURCE:

Raw Wastewater Endogenous Respiration Supplemental Carbon

Anoxic Conditions in Mixed Liquor

(Anoxic & Post Anoxic Zones)

N2(g)

cBOD

Denitrifying Biomass

Nitrate Biomass Carbon (BOD) Anoxic Conditions

Keys to Denitrification

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NO3-N

Single Sludge Nitrification

Aeration Tank Influent

BOD Removal, Nitrification

RAS Pump Effluent Secondary Clarifier Waste Sludge

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Wuhrman Process

Aeration Tank Influent

BOD Removal, Nitrification

RAS Pump Effluent Secondary Clarifier Waste Sludge

BOD Removal, Nitrification & Denitrification

Anoxic Tank

Which of the 4 Factors will most likely limit denitrification? ORGANIC CARBON

Single Sludge Nitrification

Aeration Tank Influent

BOD Removal, Nitrification

RAS Pump Effluent Secondary Clarifier Waste Sludge

BOD Removal, Nitrification & Denitrification

Anoxic Tank

Ludzack-Ettinger Process

NITRATE Which of the 4 Factors will most likely limit denitrification?

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Single Sludge Nitrification

Aeration Tank Influent

BOD Removal, Nitrification

RAS Pump Effluent Secondary Clarifier Waste Sludge

BOD Removal, Nitrification & Denitrification

Anoxic Tank

Ludzack-Ettinger Process Modified Ludzack-Ettinger (MLE) Process

Nitrified Recycle (IMLR)

Which of the 4 Factors will most likely limit denitrification?

MLE Recycle Relationship (Internal ML Recycle)

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 0% 50% 100% 150% 200% 250% 300% 350% 400% 450% Mixed Liquor Recycle (% of Influent)

Theoretical Denitrification Possible (% of Total NO3-N)

%Denit from MLR Only %Denit from MLR + 50%RAS %Denit from MLR + 100%RAS

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Process Simulator – ML Recycle Example

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Influent Nitrogen Concentrations

  • Conventional Pollutants
  • BOD5

200 mg/L

  • TSS

200 mg/L

  • Unoxidized Nitrogen:
  • Ammonia N (NH3-N)

20 mg/L

  • Organic Nitrogen

20 mg/L

  • Total Kjeldahl Nitrogen (TKN)

40 mg/L

  • Oxidized Nitrogen:
  • Nitrite (NO2-N)

0 mg/L

  • Nitrate (NO3-N)

0 mg/L

  • Total Oxidized Nitrogen

0 mg/L

  • Total Nitrogen

40 mg/L

Nitrogen Concentration by Level of Treatment

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Evaluating and Improving Denitrification

UNDERSTAND THE LIMITING FACTORS NITRATE BIOMASS CARBON

Increase Nitrate Mass to Anoxic Conditions Increase Biomass operating under Anoxic Conditions

  • Increase Anoxic Volume
  • Increase MLSS

Increase/Improve Carbon Source

ANOXIC CONDITIONS

Decrease Dissolved Oxygen Input

  • Supplemental Source (methanol,

Micro-C)

  • Primary Clarifier Bypass
  • Fermentation
  • Dissolved Oxygen Control
  • D.O. Exhauster Zone
  • Increase IMLR Flow

Post- Denitrification

  • Often required to achieve very low TN Levels (<5 mg/L)
  • Carbon source is often the key factor
  • Endogenous respiration
  • Supplemental carbon addition
  • Activated Sludge Options
  • Single Sludge
  • Separate Sludge
  • Fixed Film Options
  • Denitrification Filters
  • Moving Bed Biofilm Reactors (MBBR)

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Modified Ludzack-Ettinger (MLE) Process

Aeration Tank Influent

BOD Removal, Nitrification

RAS Pump Effluent Secondary Clarifier Waste Sludge

BOD Removal, Nitrification & Denitrification

Anoxic Tank Nitrified Recycle

4-Stage Bardenpho Process

Aeration Tank Influent

BOD Removal, Nitrification

RAS Pump Effluent Secondary Clarifier Waste Sludge

BOD Removal, Nitrification & Denitrification

Anoxic Tank Nitrified Recycle Anoxic Tank Post-Aeration Tank Supplemental Carbon

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Separate Sludge 5-Stage Bardenpho Process

BOD Removal, Nitrification, Denitrification & Phosphorus

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

Methanol

Waste Sludge Anaerobic Tank Secondary Clarifier RAS Pump Waste Sludge

Process Simulator – 4-Stage Example

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Summary of Nitrification vs. Denitrification

Nitrate Nitrate Aerobic Aerobic Anoxic Anoxic

FINAL PRODUCT ENVIRONMENTAL CONDITIONS BIOMASS INVOLVED OXYGEN ALKALINITY

Nitrogen Gas Nitrogen Gas Heterotrophs – Fast Growth Heterotrophs – Fast Growth Recovers Oxygen

(2.9 lb O2/ lb NH4-N)

Recovers Oxygen

(2.9 lb O2/ lb NH4-N)

Produces Alkalinity

(3.6 lb CaCO3/ lb NH4-N)

Produces Alkalinity

(3.6 lb CaCO3/ lb NH4-N)

Autotrophs – Slow Growth Autotrophs – Slow Growth Consumes Oxygen

(4.6 lb O2/ lb NH4-N)

Consumes Oxygen

(4.6 lb O2/ lb NH4-N)

Consumes Alkalinity

(7.2 lb CaCO3/ lb NH4-N)

Consumes Alkalinity

(7.2 lb CaCO3/ lb NH4-N)

Nitrification Denitrification

Hydromantis Denitrification Case Study

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Total Nitrogen (TN) Removal Case Study

  • Green Valley WRF

Pima County, AZ

  • Biological Nitrogen Removal
  • Nitrification and Denitrification
  • 4.1 MGD capacity:
  • 2.1 MGD Aerated Ponds
  • 2.0 MGD Oxidation Ditch

TN Removal With ON/OFF Aeration

  • Conventional denitrification uses an aerobic zone for

nitrification and an anoxic zone for denitrification

  • Both can be achieved in a single tank by alternating

between aerobic and anoxic conditions

  • Aerobic conditions = nitrification
  • Anoxic conditions = denitrification

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TN Removal With ON/OFF Aeration

  • Aerobic conditions promote nitrification (Ammonia  Nitrate)

Anoxic conditions promote denitrification (Nitrate  N2 gas)

TN Removal With ON/OFF Aeration

  • Control systems can optimize the TN removal by

adjusting the cycle times for varying loads/temperatures

  • There is a sweet spot of low-DO “partial aeration” where

nitrification and denitrification can occur simultaneously

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TN Removal With Low-DO Aeration

  • Low aeration allows for a combination of aerobic and anoxic

conditions

TN Removal With Low-DO Aeration

  • Low aeration allows for a combination of aerobic and anoxic

conditions

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TN Removal With Low-DO Aeration

  • Low aeration allows for a combination of aerobic and anoxic

conditions

  • Low DO conditions can, however cause
  • ther issues:
  • Potential to grow filamentous biomass
  • Settlement of solids

Green Valley WRF (Pima County, AZ)

Influent Headworks Emergency Overflow Basin Secondary Clarifiers Oxidation Ditch Disinfection RAS/WAS Pumping Solids Handling

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Green Valley WRF (Pima County, AZ) Green Valley WRF – Aeration / DO Control

  • 4 Rotors:
  • Independent control
  • DO Controller:
  • DO is average of

tanks 5 and 12

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Green Valley WRF – Aeration / DO Control

  • Sequencing rotors:
  • Switched ON/OFF to

meet setpoint

  • If DO > Setpoint
  • Turn OFF the rotor that

has been running the most

  • If DO < Setpoint
  • Turn ON the rotor that

has been running the least

DO Setpoint: 0.4 mg/L Sensor: 0.25 mg/L R1: 0 min R2: 0 min R3: 0 min R4: 0 min R1: 10 min R2: 0 min R3: 0 min R4: 0 min DO Setpoint: 0.4 mg/L Sensor: 0.35 mg/L DO Setpoint: 0.4 mg/L Sensor: 0.39 mg/L R1: 20 min R2: 0 min R3: 10 min R4: 0 min DO Setpoint: 0.4 mg/L Sensor: 0.44 mg/L R1: 30 min R2: 10 min R3: 20 min R4: 0 min DO Setpoint: 0.4 mg/L Sensor: 0.38 mg/L R1: 30 min R2: 20 min R3: 30 min R4: 0 min DO Setpoint: 0.4 mg/L Sensor: 0.43 mg/L R1: 30 min R2: 30 min R3: 40 min R4: 10 min What rotor action happens next? Rotor 3: OFF

Green Valley WRF (Pima County, AZ)

  • Denitrification Study:
  • Start from conditions

resulting in high effluent Total Nitrogen (TN)

  • What changes are required

to get effluent TN to < 7.0 mgN/L?

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Green Valley WRF (Pima County, AZ)

  • Run 1:
  • All 4 rotors ON

Green Valley WRF (Pima County, AZ)

  • Run 2:
  • 3 rotors ON

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Green Valley WRF (Pima County, AZ)

  • Run 3:
  • DO Control

Setpoint = 0.6 mg/L

Green Valley WRF (Pima County, AZ)

  • Run 4:
  • DO Control

Setpoint = 0.2 mg/L

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Green Valley WRF (Pima County, AZ)

  • Run 5:
  • DO Control

Setpoint = 0.375 mg/L

DO Control - Finding the Sweet Spot

  • Too much or too little aeration can move away from the
  • ptimal point:
  • Too high DO  higher nitrate
  • Too low DO  higher ammonia

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Comparison

  • Summary of simulation results:

# Description Effluent TN (mg/L) Avg DO (mg/L) Avg Aerator On- Time (hr/d) Energy Cost ($/yr) 1 All Rotors On 32.9 1.65 24 $145,600 2 3 Rotors On 15.7 0.53 18.1 $117,000 3 DO Control 0.6 mg/L 5.5 0.5 - 0.6 16.4 $108,800 4 DO Control 0.2 mg/L 6.4 0.17 - 0.2 11.5 $85,200 5 DO Control 0.375 mg/L 4.6 0.35 - 0.4 14.1 $97,600

Case Study Summary

  • Simultaneous nitrification/denitrification is an effective

way to optimize for TN removal while optimizing energy usage

  • Green Valley WRF uses a sophisticated control system to

manage treatment performance and energy use

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Questions?

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

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