ACTIVATED SLUDGE ACTIVATED SLUDGE

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SEPARATION OF SEPARATION OF

ACTIVATED SLUDGE ACTIVATED SLUDGE

PROBLEMS PROBLEMS

Written case study on water treatment problems

Presented b

Presented b y y : : Hala Hala Almshawit Almshawit

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Introduction:

Activated sludge represent Activated sludge represent

biological wastewater treatment in biological wastewater treatment in WWTP WWTP

Treatment of wastewater from Treatment of wastewater from biomass newly formed by

biomass newly formed by

microbial growth in secondary microbial growth in secondary settling tank.

settling tank.

If this part of the activated sludge If this part of the activated sludge process fails!

process fails!

We need to know: We need to know :

¾¾

What is the structure of activated What is the structure of activated sludge

sludge ? ?

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What is a well- What is a well -settled activated settled activated sludge?

sludge?

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Floc components

Paramecium sp. Vorticella sp. Zoogloea sp.

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Well settled activated sludge Well settled activated sludge

Overflow rate (v)= )= QeQe / A 0.7 / A 0.7 -- 1.4 1.4 m/hm/h

Sludge VolumSludge Volum Index (SVI):Index (SVI):

SVI < 120 satisfactory.

SVI > 150 bulking.

It leaves a clear supernatant after It leaves a clear supernatant after sedimentation.

sedimentation.

WSAS do not interfere during WSAS do not interfere during sedimentation and thickening.

sedimentation and thickening.

Does not rise and float within at Does not rise and float within at least a 2

least a 2--3 h period after 3 h period after sedimentation.

sedimentation.

Cone Cone settleabilitysettleability :The important :The important thing is stability

thing is stability

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1 1 - - Dispersed growth: Dispersed growth:

Visual observation : Visual observation :

Individual cells or small clumps with diameter of up Individual cells or small clumps with diameter of up 10 10 - - 20 20 µ µ m. m.

The sedimentation rate is too low for gravity The sedimentation rate is too low for gravity sedimentation, and no zone settling occurs in sedimentation, and no zone settling occurs in secondary settling tanks.

secondary settling tanks.

Principal causes:

Low production of extracellular polymers substances Low production of extracellular polymers substances

which can have two causes:

High concentration of readily degradable substrates High concentration of readily degradable substrates

The presence of some toxic or inhibitory compounds The presence of some toxic or inhibitory compounds in wastewater.

in wastewater.

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2- Formation of microflocs (pinpoint flocs):

Visual observation:

Larger dimension (about 50-Larger dimension (about 50-100100µµm) particles m) particles have roughly spherical and compact form.

have roughly spherical and compact form.

Filaments not predominant ,and cone settleabilityFilaments not predominant ,and cone settleability test may show some well

test may show some well-- settling material settling material but a cloudy supernatant.

but a cloudy supernatant.

Principal causes:

High sludge age (low concentrations of exogenousHigh sludge age (low concentrations of exogenous substrates (endogenous metabolism)) the destruction substrates (endogenous metabolism)) the destruction

of EPS of activated sludge will occur.

Macrostructure failure, when the filamentous Macrostructure failure, when the filamentous microorganisms disappear.

microorganisms disappear.

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Solutions:

Redesigning secondary settling tanks to be more Redesigning secondary settling tanks to be more suitable to

suitable to reflocculation reflocculation process. process.

All structures with high turbulence, should be All structures with high turbulence, should be avoided.

avoided.

Keep F/M ratio in the range 0.05 to 0.2 Keep F/M ratio in the range 0.05 to 0.2

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3 3 - - Viscous bulking: Viscous bulking:

Principal causes:

Excessive EPS production by Excessive EPS production by microorganisms.

microorganisms.

!!! lack of nutrients/micronutrients (F/M too !!! lack of nutrients/micronutrients (F/M too low).

low).

Dissolved oxygen too low.Dissolved oxygen too low.

Toxic compounds (mainly chromium and Toxic compounds (mainly chromium and sulphide

sulphide).).

High presence of Zoogloea “High presence of Zoogloea “animal glueanimal glue””::

¾¾ Readily biodegradable substrates VFA,Readily biodegradable substrates VFA,

¾

¾ Excessive anoxic retention.Excessive anoxic retention.

Visual observation:

Poor sludge dewaterabilityPoor sludge dewaterability..

Diluted return (and waste) activated sludge.Diluted return (and waste) activated sludge.

When it is intensively aerated, a foaming When it is intensively aerated, a foaming may appear.

may appear.

The activated sludge sticky.The activated sludge sticky.

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3 3 - - Viscous bulking: Viscous bulking:

Solutions Solutions : :

Ozonation Ozonation leads to replacing of open structures of fingered leads to replacing of open structures of fingered zoogloeal

zoogloeal colonies by dense compact flocs. colonies by dense compact flocs.

Addition of synthetic Addition of synthetic cationic polymers or minerals. cationic polymers or minerals.

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4 4 - - Rising sludge: Rising sludge:

Visual observation:

In glass cylinder, two phases can be In glass cylinder, two phases can be distinguished:

distinguished:

-- First the activated sludge settles rapidly First the activated sludge settles rapidly

(compact bottom layer of settled sludge and (compact bottom layer of settled sludge and a clear supernatant).

a clear supernatant).

-- Sludge starts to float and move up to the Sludge starts to float and move up to the water surface.

water surface.

Rising sludge flocs will escape from clarifiers.Rising sludge flocs will escape from clarifiers.

Princible causes:

The bubbles of nitrogen act as a sludge carrier .The bubbles of nitrogen act as a sludge carrier .

A critical nitrate concentration for sludge rising at A critical nitrate concentration for sludge rising at 20°20°C is about 6C is about 6-8mg/l (NO-8mg/l (NO³³ –– N).N).

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Solutions:

Decrease nitrate Decrease nitrate

concentration below the concentration below the critical value.

critical value.

Installing baffles to Installing baffles to

protect the effluent weirs

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5 5 - - Filamentous bulking: Filamentous bulking:

Visual observation : Visual observation :

Hydraulic overloading of sludge. Hydraulic overloading of sludge.

Increase SVI and cone Increase SVI and cone settleability settleability Principal causes:

Principal causes:

Presence of filamentous bacteria inside Presence of filamentous bacteria inside the floc.

the floc.

The filaments, prevent the compaction The filaments, prevent the compaction of individual flocs.

of individual flocs.

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Solutions:

Identification of the causative Identification of the causative filament(sfilament(s) leads to specific ) leads to specific remedies

remedies

Causative Condition Filament Types Control

Low DO Type 1701 Adjust the aeration rates Limited Nutrients Thiothrix sp. Nutrient addition,BOD

(N or P) ratio of 100:5:1 suggested

Materials and Polymers Addition:Materials and Polymers Addition:

Coagulants/precipitants such as lime or ferric chloride.

Toxicants as chlorine and hydrogen peroxide.

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6- Foaming caused by filamentous microorganisms

Visual observation/

Visual observation/Characterisation:Characterisation:

It is a system of three phases-It is a system of three phases-airair-water-water-- microbial cells (hydrophobic cells).

microbial cells (hydrophobic cells).

Escape from aeration basin to the secondary Escape from aeration basin to the secondary settling tank.

settling tank.

If temperature drops below freezing point, If temperature drops below freezing point, the foam freezes.

the foam freezes.

Principal causes:

EPS has surface active agents properties EPS has surface active agents properties ((biosurfactants).biosurfactants).

The cell walls of foam forming microorganism The cell walls of foam forming microorganism are hydrophobic.

are hydrophobic.

Dosing of fatty compounds into influent Dosing of fatty compounds into influent

wastewater lead to biological foam creation.

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Solutions Solutions

Dilution. Dilution.

Using Antifoams/ Using Antifoams/ Defoamers Defoamers . .

Mechanical remove of scum Mechanical remove of scum as much as possible before as much as possible before clarifiers, and should be not clarifiers, and should be not recycled back into the plant.

recycled back into the plant.

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Monitoring Monitoring

Control parameters:

Microscopic examination of sludge. Microscopic examination of sludge.

Dissolved Oxygen (DO).Dissolved Oxygen (DO).

BOD (or COD) load. BOD (or COD) load.

Nutrient requirements.Nutrient requirements.

F/M loading. F/M loading.

Sludge age (Mean Cell Residence Time). Sludge age (Mean Cell Residence Time).

Mixed liquor suspended solids (MLSS). Mixed liquor suspended solids (MLSS).

UpflowUpflow velocity (clarifier).velocity (clarifier).

PH value.PH value.

Cone settleabilityCone settleability. .

Sludge volume index (SVI). Sludge volume index (SVI).

Surplus sludge production. Surplus sludge production.

Mixing considerations. Mixing considerations.

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Conclusion Conclusion

The problems related to the presence of The problems related to the presence of filamintous

filamintous organisms or EPS production. organisms or EPS production.

The best approach is to investigate the The best approach is to investigate the long term control methods suitable for long term control methods suitable for

your plant.

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References References

Madigan,Martinko,andMadigan,Martinko,and Parker.NinthParker.Ninth Edition.BrockEdition.Brock Biology of Biology of Microorganism.ISBN:0

Microorganism.ISBN:0--1313--081922081922--2.2.

J.WannerJ.Wanner. Activated sludge bulking and foaming control.ISBN. Activated sludge bulking and foaming control.ISBN No.1-No.1-5667656676-- 121121-2. (Activated sludge separation problems p: 87-2. (Activated sludge separation problems p: 87--111).111).

Loy A, Wagner M: Bacterial community composition and function inLoy A, Wagner M: Bacterial community composition and function in sewage sewage treatment systems. Current Opinion in Biotechnology 2002, 13:218

treatment systems. Current Opinion in Biotechnology 2002, 13:218–227–227

yanyan Liu, Herbert H.P. Fang:influencesLiu, Herbert H.P. Fang:influences of Extracellular Polymeric of Extracellular Polymeric Substances(EPS

Substances(EPS) on Flocculation, Settling and Dewatering of Activated ) on Flocculation, Settling and Dewatering of Activated Sludge.Critical

Sludge.Critical Reviews in Environmental SceinceReviews in Environmental Sceince and Technology,33(3):237-and Technology,33(3):237- 273 273

http://www.ensic.unancy.fr/COSTWWTP/Work_Group/Wg4/Lisboa/Wannerhttp://www.ensic.unancy.fr/COSTWWTP/Work_Group/Wg4/Lisboa/Wanner_p_p res.pdf

res.pdf

http://www.activatedsludge.info/http://www.activatedsludge.info/

http://www.college.ucla.edu/webproject/micro7/studentprojects7/Rhttp://www.college.ucla.edu/webproject/micro7/studentprojects7/Rader/asluader/aslu dge2.htm

dge2.htm

http://www.tramfloc.com/antifoamhttp://www.tramfloc.com/antifoam-select.doc-select.doc

http://www.envirocentre.ie/downloads/BPDCS002%20wastewater.pdfhttp://www.envirocentre.ie/downloads/BPDCS002%20wastewater.pdf

http://www.dec.state.ny.us/website/dow/bwcp/ta_sludbulk.htmlhttp://www.dec.state.ny.us/website/dow/bwcp/ta_sludbulk.html

http://www.h2o2.com/applications/municipalwastewater.htmlhttp://www.h2o2.com/applications/municipalwastewater.html

http://www.aquanova.czhttp://www.aquanova.cz

http://www.tramfloc.com/tf38.htmlhttp://www.tramfloc.com/tf38.html

http://www.environmentalleverage.com/What%20are%20Filamentous%20http://www.environmentalleverage.com/What%20are%20Filamentous%20BaBa cteria.htm

cteria.htm

http://www.engitech.com/asm.htmhttp://www.engitech.com/asm.htm

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Contenents:

Introduction Introduction

Flocs components Flocs components

Well settled activated sludge characteristics Well settled activated sludge characteristics

Activated sludge separation from treated Activated sludge separation from treated wastewater Problems

wastewater Problems . .

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Problem description Problem description

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Solution Solution

Monitoring Monitoring

Conclusion Conclusion

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ACTIVATED SLUDGE ACTIVATED SLUDGE

SEPARATION OF SEPARATION OF