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8/16/2019 Module 4 - Activated Sludge Process Control
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Activated SludgeProcess Control
by
R. Dale Richwine, P.E.
Richwine Environmental, Inc.
Session Overview
» Sludge Quality
– Visual Observations
– Use of Settlometer
» Sludge Quantity
– System Inventory
– Solids Management
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Sludge Quality
»
Visual Observations
»
Use of Settlometer
Sludge QualityVisual Observations
» Aeration Basins
– Foam Color
– Diffuser Pattern
» Secondary Clarifiers
– Quantity of Foam
– Effluent Quality
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Visual ObservationsAeration Basin Foam
Fresh Crisp White Foam
Visual ObservationsAeration Basin Foam
Excessive Billowing
White Foam
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Visual ObservationsAeration Basin Foam
Thick, Scummy, DarkBrown Foam
Nocardia Foam (200X)
Visual ObservationsAeration Basin Foam
Proper Foam
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Visual ObservationsDiffuser Pattern
Fine Bubble Coarse Bubble
Visual ObservationsDiffuser Pattern
Diffuser Problems
Can Cause Dead Spots
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Visual ObservationsClarifier Foam
Visual ObservationsEffluent Quality Problems
Poor Treatment
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Visual ObservationsEffluent Quality Problems
Sludge Bulking
Visual ObservationsEffluent Quality Problems
Sludge Solids Washout
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Visual ObservationsEffluent Quality Problems
Clumping
Clumping
Visual ObservationsEffluent Quality Problems
Ashing
Ashing may be asymptom of
overoxidized
(overaerated) mixed
liquor.
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Visual ObservationsEffluent Quality Problems
Straggler Floc
Straggler floc is indicative
of a low SRT
Visual ObservationsEffluent Quality Problems
Pin Floc
– Carryover of very fine material infinal effluent
– Turbid or milky appearance of finaleffluent
Possible Causes
of Pinpoint Floc
– Old sludge with poor floc-forming
characteristics – Excessive turbulence shearing the
floc.
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Sludge QualityUse of Settlometer
Settlometer Test
– Sample AerationBasin Effluent
– Run test
immediately
following
sampling
–
Handle samplewith care
Use of SettlometerSettlometer Test
» Original Test
– 1 liter graduatedcylinder
» Mallory Settlometer
– 2-liter container
– Graduated to 1000 ml/L
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Use of SettlometerSettlometer Test
Sample Handling
– Collect sample in wide-mouth bottle
– Start test immediately
– Minimize agitation of sample
Use of SettlometerSettlometer Test
Four Phases of Settling
– Flocculation
– Blanket Formation
– Settling
– Compaction
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Use of SettlometerSettlometer Test
What to watch for
SettlingRate
Characteristicsof Interface
Clarity of Supernatant
Use of SettlometerSettlometer Test
Take Readings – Every 5-minutes
– Up to 30-minutes
– Every 10-minutes
– Up to 60-minutes
– After 4-hours
Note Observations – Supernatant
quality
– Type of interface
– Surface
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Use of SettlometerSettlometer Test
Settled Sludge Volume
– SSV
Cleanwater Treatment Plant
0
200
400
600
800
1000
1200
0 10 20 30 40 50 60
Sludge Settling Time (minute s)
S S V
( c c / L )
0
2
4
6
8
10
12
14
16
S S C ( m g / L )
Use of SettlometerSettlometer Test
»
Settled Sludge
Concentration
– SSC
SSV/MLSSSSC=
Cleanwater Treatment Plant
0
200
400
600
800
1000
1200
0 10 20 30 40 50 60
Sludge Settling Time (m inutes)
S S V
( c c / L )
0
2
4
6
8
10
12
14
16
S S C ( m g / L )
MLSS = 2500mg/L
Calculation
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Use of SettlometerSettlometer Test
Fast Settling Sludge
Cleanwater Treatment Plant
0
100
200
300
400
500
600
700
800
900
1000
0 10 20 30 40 50 60
Sludge Settling Time (minutes)
S S V
( c c
/ L )
0
2
4
6
8
10
12
14
16
S S C ( m g / L )
MLSS = 2500mg/L
Cleanwater Treatment Plant
0
100
200
300
400
500
600
700
800
900
1000
0 10 20 30 40 50 60
Sludge Settling Time (minutes)
S S V
( c c / L )
0
2
4
6
8
10
12
14
16
S S C ( m g / L )
MLSS = 2500mg/L
Slow Settling Sludge
Use of SettlometerSludge Volume Index (SVI)
Data Required
– The SSV30 from Settlometer Test
– MLSS concentration of the sample
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Use of SettlometerSludge Volume Index (SVI)
)(MLSS
)/(1000)/(SSV)/(SVI 30
mg/L
g mg LmLml g
!
=
Target range: 75 - 150 mL/g
but IT DEPENDS!
The volume occupied by 1 gram of MLSS after
30 minutes of settling.
Sludge Quantity
System Inventory
– Mass of solids in system
Solids Management
– Return Sludge Rate
– Wasting Rate
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System Inventory
» Aeration Basin MLSS
» Clarifier Solids (Blanket)
Goals
– Manage Inventory to Match Optimum Growth Rate
– Maintain Consistent Inventory of Solids
System Inventory
Manage Inventory to Match Optimum Growth
– Determine optimum F/M or Growth Rate
Growth Rate
– Sludge Age
– Age
– MCRT
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System Inventory
Aeration Basin Solids
Clarifier Solids
System InventoryMaintain Consistent Inventory
Inventory Management Tools
– Return Sludge Rate
– Wasting Rate
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System InventoryReturn Sludge Rate
Cleanwater Treatment Plant
0
200
400
600
800
1000
1200
0 10 20 30 40 50 60
Sludge Settling Time (minutes)
S S V
( c c / L )
0
2
4
6
8
10
12
14
16
S S C ( m g / L )
MLSS = 2500mg/L
Optimum Return SludgeConcentration is determined
by Quality of MLSS
Desired RAS
Concentration
System InventoryReturn Sludge Rate
RAS Rate Calculation
)MLSSSSC(
)MLSSRAS(RateRASCurrent(gpm)RateFlowRASDesired
!
!"
=
t
Conc
Where:
• Desired RAS Flow Rate (gpm) = Optimum RAS Flow (gpm)
•
Current RAS Rate = Current RAS Flow (gpm)
• RAS Conc = Return Sludge Concentration (mg/L)
• MLSS = Mixed Liquor Suspended Solids (mg/L)
• SSCt = Settled Sludge Concentration at desired time
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System InventoryMaintain Consistent Inventory
Sludge Wasting
– Change rate slowly
– Use 5-day average
Control Process Using Sludge Age
OutSolidsInventoryAgeSludge !=
System InventorySludge Age
Data Required
– Solids under aeration in the aeration basin, pounds(lbs)
– Clarifier Solids (lbs)
– Secondary effluent suspended solids (SESS) from
previous day, lbs/day
– Solids intentionally wasted from the process (WAS),pounds per day (lbs/day)
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System InventorySludge Age
(lbs/day)SESS(lbs/day)WAS
(lbs)InventoryBasinAeration(days)SRT
+
=
(lbs/day)SESS(lbs/day)WAS
(lbs)InventoryClarifier(lbs)InventoryBasinAeration(days)MCRT
+
+
=
Sludge Retention Time, Sludge Age, Age
Mean Cell Residence Time (MCRT)
System InventoryWasting
Data Required
– Solids under aeration in the aeration basin (inventory),pounds (lbs)
– Secondary effluent suspended solids from the previousday (SESS), pounds per day (lbs/day)
– Desired sludge residence time (SRT), days
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System InventoryWasting
/day)((days)SRTDesired
(lbs)InventorySolidsSystem (lbs/day)AS lbsSESS W !=
Where:
• System Solids Inventory = Aeration Basins Inventory (lbs)
+ Clarifier Inventory (lbs) *** Clarifier Inventory only used if desired• Desired SRT (days) = Sludge Age Set as Process Goal
• SESS (lb/day) = Secondary Effluent TSS (mg/L) * 8.34 * Plant Flow (mgd)
System InventoryFood to Microorganism Ratio (F/M)
Data Required
– Primary effluent flow (Q), mgd
– Primary effluent cBOD, mg/L
– MLVSS concentration, mg/L
– Aeration basin volume, million gallons
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System InventoryFood to Microorganism Ratio (F/M)
)/(8.34)/(MLVSS)(VolumeBasinAeration
)/(8.34)/(cBODPE)(QPEF/M
gal lb Lmg MG
gal lb Lmg mgd
!!
!!
=
(lbs)AerationUnderBiomass
(lbs)BasinAerationIntocBODF/M =
)/(MLVSS)(VolumeBasinAeration
)/(cBODPE)(QPEF/M
Lmg MG
Lmg mgd
!
!
=
System InventoryFood to Microorganism Ratio (F/M)
Interpretation of F/M Values
0.04 – 0.15 Extended Aeration
0.20 – 0.50 Convention Activated Sludge
0.50 – 1.50 High-rate Processes
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Session Summary
Sludge Quality
– Visual Observations
– Use of Settleometer
Sludge Quantity
– System Inventory
– Solids Management
Activated Sludge Process Control
» Basics – BOD update rate = Bacterial Growth Rate
» Growth Factors
» Sludge Quality – Visual Observations
– Use of Settlometer
» Sludge Quantity
– System Inventory
–
Solids Management
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One Thing to Remember
Rate of Removal = Rate of Biomass Growth