ammonia-based aeration control (abac) · 2018-04-18 · 9 control objectives – ammonia-based...
TRANSCRIPT
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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
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HRSD Nansemond Treatment Plant
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Plant Schematic
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5-Stage Configuration
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Instrument Locations
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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
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Process Flow Diagram
NO3 DO NO2 OP NH4
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Ammonia-based Aeration Control
(ABAC)
Nansemond Treatment Plant
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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
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• To decrease – Supplemental carbon
usage – Chlorine demand – Energy consumption – Alkalinity demand
• To optimize overall plant operations
Motivation
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Model Predictions – Benefits of ABAC
Results from Modeling
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M
DO Controller
Manipulated variable
Measured variable
O2
12
Conventional DO Concentration Control
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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
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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
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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
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Model Predictions – Benefits of ABAC
Results from Modeling
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Key Instruments for ABAC
Ammonia ISE Probe Dissolved Oxygen Probe
Zone 1
Zone 2 Zone 3
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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
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Instrumentation and Automation
Ammonia Dissolved Oxygen
Zone 1
Zone 2 Zone 3
NH4 Controller
DO Controller
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Control Mode Configuration
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Aeration Tanks in Operation
DO Mode ABAC Mode ABAC Mode
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Average Dissolved Oxygen Concentrations during DO Control
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Average Dissolved Oxygen Concentrations during ABAC
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Operation of ABAC
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Operation of ABAC
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Operation of ABAC
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Ideal Operation of ABAC
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Ideal Operation of ABAC
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Ideal Operation of ABAC
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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
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Nansemond Plant Monthly Energy
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Supplemental Carbon Usage
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Supplemental Carbon Cost
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Final Effluent (FNE) Nutrient Concentrations during Operation in DO Control and ABAC
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Final Effluent (FNE) Nutrient Concentrations during Operation in DO Control and ABAC
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Use of ABAC Average Auto DO Setpoint to Control SRT
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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