activated sludge process control - lower columbia section workshop - feb2012... · 1 activated...

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Activated Sludge Process 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 Quality Visual Observations

» Aeration Basins –  Foam Color –  Diffuser Pattern

» Secondary Clarifiers –  Quantity of Foam –  Effluent Quality

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Visual Observations Aeration Basin Foam

Fresh Crisp White Foam

Visual Observations Aeration Basin Foam

Excessive Billowing White Foam

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Visual Observations Aeration Basin Foam

Thick, Scummy, Dark Brown Foam

Nocardia Foam (200X)

Visual Observations Aeration Basin Foam

Proper Foam

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Visual Observations Diffuser Pattern

Fine Bubble Coarse Bubble

Visual Observations Diffuser Pattern

Diffuser Problems Can Cause Dead Spots

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Visual Observations Clarifier Foam

Visual Observations Effluent Quality Problems

Poor Treatment

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Visual Observations Effluent Quality Problems

Sludge Bulking

Visual Observations Effluent Quality Problems

Sludge Solids Washout

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Visual Observations Effluent Quality Problems

Clumping Clumping

Visual Observations Effluent Quality Problems

Ashing

Ashing may be a symptom of overoxidized

(overaerated) mixed liquor.

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Visual Observations Effluent Quality Problems

Straggler Floc

Straggler floc is indicative of a low SRT

Visual Observations Effluent Quality Problems

Pin Floc

–  Carryover of very fine material in final effluent

–  Turbid or milky appearance of final effluent

Possible Causes of Pinpoint Floc

–  Old sludge with poor floc-forming

characteristics –  Excessive turbulence shearing the

floc.

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Sludge Quality Use of Settlometer

Settlometer Test –  Sample Aeration

Basin Effluent –  Run test

immediately following sampling

–  Handle sample with care

Use of Settlometer Settlometer Test

» Original Test –  1 liter graduated

cylinder » Mallory Settlometer

–  2-liter container –  Graduated to 1000 ml/L

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Use of Settlometer Settlometer Test

Sample Handling –  Collect sample in wide-mouth bottle –  Start test immediately –  Minimize agitation of sample

Use of Settlometer Settlometer Test

Four Phases of Settling –  Flocculation –  Blanket Formation –  Settling –  Compaction

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Use of Settlometer Settlometer Test

What to watch for

Settling Rate

Characteristics of Interface

Clarity of Supernatant

Use of Settlometer Settlometer 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 Settlometer Settlometer 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 (minutes)

SSV (cc

/L)

0

2

4

6

8

10

12

14

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SSC (mg/L)

Use of Settlometer Settlometer 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 (minutes)

SSV (

cc/L)

0

2

4

6

8

10

12

14

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SSC (mg/L)

MLSS = 2500mg/L

Calculation

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Use of Settlometer Settlometer 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)

SSV (

cc/L)

0

2

4

6

8

10

12

14

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SSC (mg/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)

SSV (

cc/L)

0

2

4

6

8

10

12

14

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SSC (mg/L)

MLSS = 2500mg/L

Slow Settling Sludge

Use of Settlometer Sludge Volume Index (SVI)

Data Required –  The SSV30 from Settlometer Test –  MLSS concentration of the sample

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Use of Settlometer Sludge Volume Index (SVI)

)(MLSS)/(1000)/(SSV)/(SVI 30

mg/LgmgLmLmlg ×

=

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 Inventory Maintain Consistent Inventory

Inventory Management Tools –  Return Sludge Rate –  Wasting Rate

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System Inventory Return Sludge Rate

Cleanwater Treatment Plant

0

200

400

600

800

1000

1200

0 10 20 30 40 50 60

Sludge Settling Time (minutes)

SSV (

cc/L)

0

2

4

6

8

10

12

14

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SSC (mg/L)

MLSS = 2500mg/L

Optimum Return Sludge Concentration is determined

by Quality of MLSS

Desired RAS Concentration

System Inventory Return Sludge Rate

RAS Rate Calculation

)MLSSSSC()MLSSRAS(RateRASCurrent(gpm) Rate Flow RAS Desired

−−×

=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 Inventory Maintain Consistent Inventory

Sludge Wasting –  Change rate slowly –  Use 5-day average

Control Process Using Sludge Age

Out SolidsInventory Age Sludge −=

System Inventory Sludge 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 Inventory Sludge Age

(lbs/day) SESS (lbs/day) WAS(lbs)Inventory Basin Aeration (days) SRT

+=

(lbs/day) SESS (lbs/day) WAS(lbs)Inventory Clarifier (lbs)Inventory Basin Aeration (days) MCRT

++

=

Sludge Retention Time, Sludge Age, Age

Mean Cell Residence Time (MCRT)

System Inventory Wasting

Data Required –  Solids under aeration in the aeration basin (inventory),

pounds (lbs) –  Secondary effluent suspended solids from the previous

day (SESS), pounds per day (lbs/day) –  Desired sludge residence time (SRT), days

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System Inventory Wasting

/day)((days) SRT Desired

(lbs)Inventory Solids System (lbs/day) AS lbsSESSW −=

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 Inventory Food 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 Inventory Food to Microorganism Ratio (F/M)

)/( 8.34)/( MLVSS)( VolumeBasin Aeration )/( 8.34)/( cBOD PE)( Q PEF/M

gallbLmgMGgallbLmgmgd

××××

=

(lbs)Aeration Under Biomass(lbs)Basin Aeration Into cBODF/M =

)/( MLVSS)( VolumeBasin Aeration )/( cBOD PE)( Q PEF/M

LmgMGLmgmgd

××

=

System Inventory Food 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