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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
Recommended