Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES...

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DIGESTER FOAMING CAUSES AND SOLUTIONS CAUSES AND SOLUTIONS CWEA Math Operations and CWEA Math, Operations, and Maintenance for Biosolids Systems Seminar Seminar September 13, 2011 Steve Walker Senior Operations Specialist sw510s1.pptx/1

Transcript of Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES...

Page 1: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

DIGESTER FOAMINGCAUSES AND SOLUTIONSCAUSES AND SOLUTIONS

CWEA Math Operations andCWEA Math, Operations, and Maintenance for Biosolids Systems

SeminarSeminarSeptember 13, 2011

Steve WalkerSenior Operations Specialist

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Page 2: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

LEARNING OBJECTIVESCauses• Process control

• Operational

• Process – digester internal

Control methods• Process control

• Operational awareness

• Process monitoringProcess monitoring

Physical improvements• Installed improvements

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Installed improvements

Page 3: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

PERSONAL EXPERIENCE$3M catastrophic failure of digester roof$1M repair of “fixed” holding tank roof

Saved two other digesters from roof failuresRuined one pair of beige Dockers

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Page 4: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

WHAT CAUSED FAILURE• Over-wasted secondary

– FilamentsM h l d t i– Much more volume compared to primary

• Gas mixing system piping approach

• Plugged flame arrestors – from foam

L l i di t• Level indicator wrong– From foam entrained in contents

• Didn’t shut off mixer soon enough

• After first failure, reduced active volume created

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,organic overload of other units in service (i/s)

Page 5: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

CAUSESCAUSES

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Page 6: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

PROCESS CONTROL CAUSES

• The blend of primary sludge to secondary sludgeThe more primary sludge the better– The more primary sludge, the better

– Measured as pound to pound, not gallon to gallon

• Excessive filaments in the secondary sludge– Nocardia and microthrix parvicella add bulk and p

structure to foam

• Feed fluctuationsFeed fluctuations– Both solids loading and volume

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Page 7: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

OPERATIONAL CAUSES

• Inadequate or inconsistent mixing– Rapid changes create unpredictable resultsRapid changes create unpredictable results

– Gas binding of pump used to mixing

• Excessive and/or fine bubble mixing – Can change the specific gravity and “fluff” the contents

• Rapid change in internal pressure– Cogeneration demandsCoge e at o de a ds

– Moisture in gas handling system

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Page 8: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

OPERATIONAL CAUSES • Insufficient volume

– Liquid level too low

– Processing volume taken up by grit or scum “raft”

U it t f i f i t t ti– Units out of service for maintenance or construction

– Results in solids loading rates greater than design

• Temperature fluctuations– Created by heating or feed disruptionsCreated by heating or feed disruptions

• Rapid change in liquid level

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Page 9: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

INTERNAL CAUSES

• Microorganisms competing for food– Acid formers vs. methane (alkalinity) formers

• Surfactants– Oil and greaseg

– Overdosed polymer in thickening or dewatering processes p

There are usually multiple contributors

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Page 10: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

POTENTIAL CONTROLPOTENTIAL CONTROL METHODS

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Page 11: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

PROCESS CONTROL• Primary sludge and secondary sludge ratio

– Maximize primary solids removal efficiency

– Maximize primary BOD removal efficiency

Filaments in the wasted secondary sludge• Filaments in the wasted secondary sludge– Review operating conditions and take corrective

actionaction

• Feed fluctuationsIdeal is constant feed of comparable ol me to all– Ideal is constant feed of comparable volume to all digesters in service

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Page 12: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

OPERATIONAL CAUSES

• Insufficient volume– Confirm liquid levelq

– Confirm active volume

– Understand seasonal trends of sludge production

• Rapid change in liquid level p g q– Strive for consistent dewatering feed rates

Check valving especially after maintenance work– Check valving, especially after maintenance work

– Be suspicious of the level indicators

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Page 13: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

OPERATIONAL CAUSES

• Inadequate or inconsistent mixing– Avoid on/off control

– If problem is recirculation pump gas binding, change type

– Review directional mixing approach

• Excessive or fine bubble mixingExcessive or fine bubble mixing – Adjust equipment

• Rapid change in internal pressureRapid change in internal pressure– Strive for consistent feed

– Drain moisture traps

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– Drain moisture traps

Page 14: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

INTERNAL CAUSES

• Temperature fluctuations– No more than 1 degree F per 24 hour change – up or

down

• Avoid septic sludgeAvoid septic sludge– More acidic than fresh sludge so greater reaction with

alkalinity

• Surfactants– Review scum and FOG feed ratese e scu a d OG eed a es

– Avoid polymer overdose

O

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/14 OBSERVE SYMPTOMS; FIND CAUSES

Page 15: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

OPERATIONAL AWARENESS

Placing a digester in service

• Ramp the feed up slowly• Ramp the feed up slowly

• Avoid seeding with poor quality sludge

• Ramp up mixing system slowly

• Maintain heat throughout

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Page 16: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

OPERATIONAL AWARENESS

Taking a digester out of service

• Ramp down the mixing system slowly• Ramp down the mixing system slowly

• Lower liquid level slowly as this sludge is usually transferred to other units in service

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Page 17: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

OPERATIONAL AWARENESS

Feed strategies

• Ideal is constant loading to each unit in service

• Minimize downtime between feeding

Withdrawal strategies

• Consistent rate from all units in service

Feed disruptionsp

• Plan maintenance and construction activities

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Page 18: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

PROCESS MEASUREMENTCriteria Measurement CommentFeed volume gallons per feed cycle Equal to all units i/s

Feed volume gallons per day Equal to all units i/s

Feed solids pounds per feed cycle Equal to all units i/s

Feed solids pounds per day Equal to all units i/s

Primary solids to pounds / pounds 50% primary sludge orPrimary solids to secondary solids ratio

pounds / pounds 50% primary sludge or greater

Volatile solids pounds/cubic foot/day 0 1 0 2 Overload =Volatile solids loading rate

pounds/cubic foot/day 0.1 – 0.2. Overload = 10% greater

Gas pressure inches W. C. 16 +/- 2

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/18 Confirm, sample, analyze, record, track/trend and publish

Page 19: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

PROCESS MEASUREMENT

Criteria Measurement Comment

Liquid level feet Determines active volumeLiquid level feet Determines active volume

Freeboard feet 6 ft or greater from top

Foam depth feet MinimalFoam depth feet Minimal

Volatile acids mg/L 50 - 330

Alkalinity mg/L 1500 - 6000y g

VA/Alk ratio mg/L / mg/L 0.1 – 0.2

Temperature degrees 95 – 100F (mesophilic)

C fi l l d t k/t d d bli h

Grit accumulation feet (quarterly) Lost active volume

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Confirm, sample, analyze, record, track/trend and publish

Page 20: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

HIGH-TECH MEASURING DEVICE

Works with grit, scum and foam

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Page 21: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

MAINTENANCE

C ill t fl t if it i h th th

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Cover will not float if it weighs more than the gas can lift

Page 22: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

MAINTENANCE – FLOATING COVERS

• Wash off overflow

• Do not store anything on the roof – such as the fan used for venting during cleaning work

• Confirm the pressure relief pallet weights

• Grease the corbelsGrease the corbels

• Inspect the ballast troughs – make sure the drain ports are openports are open

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Page 23: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

PHYSICAL IMPROVEMENTS

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Page 24: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

VIEWING PORTS

Use to determine the foam depth and how much freeboard is available

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is available

Page 25: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

FOAM DEPTH GUIDE

Stainless steel; extends 9 inches away from sidewall;inches away from sidewall; 8 feet long; Z-shaped jog at every foot

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Page 26: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

MULTIPLE LEVEL INDICATORS

Compare the bubbler level to the radar level. The difference is foam.

Bubbler works off of pressure Thepressure. The specific gravity of the digester contents

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more entrained gas.

Page 27: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

MOISTURE SEPARATIONTrapped water or foam can stop gas flow.

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Page 28: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

PRESSURE RELIEF HATCHES

Containment area f ll illfor small spills

Weighted to open at 2 to 3 inches WC greater than typical gas pressure

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typical gas pressure

Page 29: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

FOAM TROUGH WITH SPRAY BAR

Allows the foam to drain out of the digester, but creates other problems whereproblems where it discharges.

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Page 30: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

WHAT WAS DISCUSSEDCauses• Process control

• Operational

• Process - internal

Control methods• Process control

• Operational awareness

• Process monitoringProcess monitoring

Physical improvements• Installed improvements

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Installed improvements

Page 31: Digester Foaming Causes and Solutions - CWEA Digester Foaming Causes and...DIGESTER FOAMING CAUSES AND SOLUTIONSCAUSES AND SOLUTIONS ... • Rapid change in internal pressure ... Foam

DIGESTER FOAMINGDIGESTER FOAMINGCAUSES AND SOLUTIONS

Thank you for being a wastewater treatment professional. Be proud of your contributions.

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professional. Be proud of your contributions.