Ammonia-Based Aeration Control (ABAC)

Charles B. Bott, PhD, PE, BCEE Director of Water Technology and Research

Hampton Roads Sanitation District

WWTP AWTP

HRSD Nansemond Treatment Plant

Plant Schematic

5-Stage Configuration

Instrument Locations

Previous BNR Aeration Strategy

1.5 mg/L 2.5 mg/L 2.5 mg/L

Zon

e 1

Zone

2

Zone

2

Zon

e 3

Zon

e 3

Process Flow Diagram

NO3 DO NO2 OP NH4

Ammonia-based Aeration Control

(ABAC)

Nansemond Treatment Plant

9

Control Objectives – Ammonia-based Aeration Control (ABAC)

Limiting aeration: Reduce energy consumption

less NH4 converted, aerating at lower dissolved oxygen, less COD oxidized

aerobically

Increase denitrification – Simultaneous Nitrification – Denitrification (SND)

Improve usage of sbCOD, reduce need for supplemental carbon

Decrease alkalinity demand

Decrease chlorine demand – NH4 is present

Maybe improve bio-P performance • Decreasing effluent ammonia peaks: Reduce the extent of

effluent ammonia peaks

• To decrease – Supplemental carbon

usage – Chlorine demand – Energy consumption – Alkalinity demand

• To optimize overall plant operations

Motivation

Model Predictions – Benefits of ABAC

Results from Modeling

M

DO Controller

Manipulated variable

Measured variable

O2

12

Conventional DO Concentration Control

M

DO Controller

Manipulated variable

Reference variable (setpoint)

Measured variable

O2

NH4 controller

DO f(NH4)

NH4

Aeration intensity control

(or intermittent aeration)

13

Feedback-only ABAC

M

DO Controller

Manipulated variable

Ref. variable

Measured variable

O2

NH4 Feedback controller

NH4

Maximum- criteria

NH4

NH4 Feedforward Controller

Q

14

Feed forward + Feedback ABAC

M

NH4 Controller

Manipulated variable

Setpoint

Measured variable

NH4

High NH4 leads to over-aeration Additional DO probe More difficult to tune

15

Implementation: Direct NH4 Control

Model Predictions – Benefits of ABAC

Results from Modeling

Key Instruments for ABAC

Ammonia ISE Probe Dissolved Oxygen Probe

Zone 1

Zone 2 Zone 3

To 2nd Stage Anoxic

Flow from Aeration Tank Zone 1

NH4 PID Controller

NH4 DO Zone 2 PID controller

Zone 2

DO probe

NH4 probe

Zone 3

DO Zone 3 PID controller

Instrumentation and Automation

Instrumentation and Automation

Ammonia Dissolved Oxygen

Zone 1

Zone 2 Zone 3

NH4 Controller

DO Controller

Control Mode Configuration

Aeration Tanks in Operation

DO Mode ABAC Mode ABAC Mode

Average Dissolved Oxygen Concentrations during DO Control

Average Dissolved Oxygen Concentrations during ABAC

Operation of ABAC

Operation of ABAC

Operation of ABAC

27

Ideal Operation of ABAC

28

Ideal Operation of ABAC

29

Ideal Operation of ABAC

Aerobic Zone Effluent Nitrate

DO Mode ABAC Mode

Nitrate concentration Aeration Tank 5 effluent Nitrate concentration Aeration Tank 7 effluent

Con

cent

ratio

n (m

g/L)

0

4

8

12

Nansemond Plant Monthly Energy

Supplemental Carbon Usage

Supplemental Carbon Cost

Final Effluent (FNE) Nutrient Concentrations during Operation in DO Control and ABAC

Final Effluent (FNE) Nutrient Concentrations during Operation in DO Control and ABAC

Use of ABAC Average Auto DO Setpoint to Control SRT

36

37

Ammonia-based Aeration Control

• Opportunities • Aeration energy savings • Supplemental carbon savings • Sodium hypochlorite savings through controlled chloramination

• Concerns

• Low DO and poor P uptake (bio-P) • NO2 accumulation and bio-P inhibition • NO2 in secondary effluent without NH4 and excessive chlorine

demand • Mixed liquor settling characteristics