module 4 - activated sludge process control

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


Excessive Billowing

White Foam


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Thick, Scummy, DarkBrown Foam

Nocardia Foam (200X)


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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Sludge Bulking


Sludge Solids Washout


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Clumping

Clumping


Ashing

Ashing may be asymptom of

overoxidized

(overaerated) mixed

liquor.


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Straggler Floc

Straggler floc is indicative

of a low SRT


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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Sample Handling

– Collect sample in wide-mouth bottle

– Start test immediately

– Minimize agitation of sample


Four Phases of Settling

– Flocculation

– Blanket Formation

– Settling

– Compaction


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What to watch for

SettlingRate

Characteristicsof Interface

Clarity of Supernatant


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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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 )


»

Settled Sludge

Concentration

– SSC

SSV/MLSSSSC=


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

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S S C ( m g / L )

MLSS = 2500mg/L

Calculation


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Fast Settling Sludge


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


0

100

200

300

400

500

600

700

800

900

1000

0 10 20 30 40 50 60


S S V

( c c / L )

0

2

4

6

8

10

12

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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


0

200

400

600

800

1000

1200

0 10 20 30 40 50 60


S S V

( c c / L )

0

2

4

6

8

10

12

14

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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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)/(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

!

!

=


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


– Solids Management

Activated Sludge Process Control

» Basics – BOD update rate = Bacterial Growth Rate

» Growth Factors

» Sludge Quality – Visual Observations

– Use of Settlometer

» Sludge Quantity


–

Solids Management


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One Thing to Remember

Rate of Removal = Rate of Biomass Growth

module 4 - activated sludge process control

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