Integrated Fixed Film Activated Sludge:Application of an Innovative Technology for High-Rate Wastewater Treatment

Leon Downing, Ph.D.David R. Jackson, P.E., BCEE

Freese and Nichols, Inc.

Agenda

Wastewater driversIntegrated Fixed Film Activated Sludge (IFAS)The Colony, TexasNitrification performanceNutrient removalDiscussion/conclusions

Wastewater Drivers

Increased nitrification requirementsEffluent discharge of 1 mgN/L or less

Decreased opportunity for footprint expansionIncreasing land costDecreasing funding

Increasing nutrient removal requirementsPhosphorusTotal nitrogen

Microbial Processes in WastewaterAerobic Processes

BOD + O2 → Biomass + CO2

NH4+-N + O2 → Biomass + NO3

--N

Anoxic Processes

BOD + NO3--N → Biomass + N2

Anaerobic Processes

VFA + PolyP → PHB + P

RAS

WAS

AER Clarifier

BOD Nitrification NO3NH4

BOD

NH4

NO3

Indianapolis, IN

Conventional Activated Sludge

BOD Stabilization

NH4+ Stabilization

Conventional Activated Sludge

Typical BOD removal needs an SRT of 3-4 daysAmmonia Nitrification requires 8-12 days (temperature dependent)

As regulations become more stringent, higher SRT is required

WastedSolidsMLSSVolumeSRT ×

=

↑SRT → ↓Solids Wasted & ↑MLSS

Conventional Activated Sludge

Increasing MLSSSolids loading rate to the clarifiersIncreased oxygen demand (Rosso and Stenstrom, 2005)

More biomass with same suspended solids?“Catch” some of the bacteria in the systemHigher total solids concentration in the systemMLSS remains the same → same solids loading rate

Integrated fixed film activated sludge (IFAS)

Hybrid treatment system that combines fixed film technology with conventional activated sludgeImmerse a solid support media into an aeration basin with suspended biological growthThe immersed media provides surface area for biological growth to attach or “park”

How IFAS Assists Nitrification

Addition of Media to an aeration basin to augment biomass concentrations

Adapted from Johnson, 2004

Figure 1 - Suspended and Fixed Film Sludge Age

02

468

1012

1416

0 10 20 30

Temperature (C)

Slud

ge A

ge (d

ays)

Suspended Growth Contribution

Attached Growth Contribution

IFAS System Alternatives

Fixed Media AlternativesTextile mesh material (“soccer net”)Provided on SS frames as sheets or tensioned nettingEntex, EIMCO, Brentwood

Floating Media AlternativesFloating sponges or plastic media (“pasta shells”)Placed directly inside aeration basin (50% or less fill volume)AnoxKaldnes, Hydroxyl PAC, USFilter Agar, Linpor

Fixed Media Systems

Floating Media Systems

The IFAS Advantage

Allows secondary treatment expansion without additional aeration basinsImproved biomass capacity…improved nitrification capacityGreater resistance to hydraulic washoutsIncrease resilience to shock loadsCan help lower suspended MLSS concentrations…improved clarifier performanceAdditional capacity for BNR RemovalImproved solids settling/better SVI characteristicsPotential for simultaneous nitrification/denitrification

Potential Disadvantages

Not a perfect fit for every plantPerformance based specificationsFixed Media Systems

Film thickness controlNuisance organisms

Floating Media SystemsRisk of media migration or lossMedia retention devices/sieves and air knives requiredPotential for hydraulic restrictions at retention sievesBest used with coarse air diffuser systems

IFAS Design Considerations

Effective fine screening and grit removalPerformance based specifications

Equivalent MLSS requirementsProcess output performance

Process performance bonds and warrantiesAeration system designMedia Containment (floating media systems)Film thickness controls

The Colony WWTP

3.39 MGD Contact Stabilization Plant 9 MGD peak 2-hour capacityTPDES Effluent Discharge Limits

10 mg/L BOD15 mg/L TSS3 mg/L NH3-N

Unable to consistently nitrify ammonia under existing process (TCEQ Agreed Order)Plant designed for 20 mg/L BOD and 20 mg/L TSS without nitrificationLimited available land for conventional expansionNeed for capacity expansion due to service area growth

The Colony WWTP

Expansion of The Colony WWTP

New headworks structure with dual fine screens and vortex grit removalInstallation of IFAS into the existing aeration basinsReplacement of aging clarifier mechanisms and conversion from series to parallel operationRetrofit existing filters with cloth disk filtrationReplace CCB with UV DisinfectionModification of sludge handling to Belt Filter Press

Expanded WWTP

4.5 MGD Hybrid Nitrification Plant (IFAS)13.5 MGD peak 2-hour capacityTPDES Effluent Discharge Limits

10 mg/L BOD15 mg/L TSS3 mg/L NH3-NInterim P reporting, Final 1 mg/L Ptotal

The Colony WWTP Design

Expansion of average daily capacity from 3.39 MGD to 4.5 MGD (33% increase) AND upgraded to nitrificationOnly two new structures (headworks and UV)Reuse or retrofit of all remaining structures and facilities (lift station, aeration basins, clarifiers, filters)Significant cost savings Minimal impact to existing land availability

IFAS Advantages

Allows secondary treatment expansion without additional aeration basinsImproved biomass inventory…improved secondary treatment and nitrification capacityAdditional capacity for BNR, critical for new Phosphorous limitGreater resistance to hydraulic washoutsOther potential benefits

Increased resilience to shock loadsImproved solids settling/better SVI characteristics

Expanded WWTP

Implementation and Startup Performance

Construction began March 2005Initial Shutdown/Construction of first train began September 6, 2005First IFAS Train brought on-line February 14, 2006Direct comparison of process performance…conventional vs. IFASFuture BNR requirements

TCEQ imposed Phosphorous limit effective upon expansion to 4.5 MGDCurrent requirement is for reporting, but future limit of 1 mg/L TPImplementation of Phase 1 BNR process designed as part of changeorder to current construction project resulting in 3 month delay

Startup loading conditions

Average Flow Rate – 1.89 MGDAverage BOD/TSS/NH3 Influent – 193/185/30 mg/LAverage BOD Loading Rate – 40#/day/1000 cfAverage Temperature during startup - 20°CMLSS design concentration – 2500 mg/LEquivalent design IFAS “MLSS” – 3500 mg/L Total “IFAS + MLSS” Inventory – 6000 mg/LEquivalent design loadings – 45#/day/1000 cf

cBOD PerformanceContact

StabilizationShut down IFAS Online

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1000

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-05

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-07

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09

MONTH

INFL

UE

NT

CB

OD

(mg/

L)

1

10

100

1000

10000

EFF

LU

EN

T C

BO

D (m

g/L

)

7 per. Mov. Avg. (EFFLUENT CBOD) 7 per. Mov. Avg. (INFLUENT CBOD)

Nitrification PerformanceContact

StabilizationShut down IFAS Online

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-05

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-07

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-08

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09

Month

EFF

LU

EN

T (m

gN/L

7 per. Mov. Avg. (Effluent)

0

5

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May-06 Aug-06 Nov-06 Feb-07 May-07 Aug-07 Nov-07 Feb-08 May-08 Aug-08 Nov-08

MONTH

INFL

UE

NT

PH

OSP

HO

RU

S(m

g/L

)

0

5

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EFF

LU

EN

T P

HO

SPH

OR

US

(mg/

L)

7 per. Mov. Avg. (EFFLUENT) 7 per. Mov. Avg. (INFLUENT)

EBPR Performance

Discussion

No special controls, simply control MLSS by wasting, just like ASOrganic and hydraulic loading rates near 10% of design limit (45 #/day/1000 cf and 2 MGD)

High levels of cBOD and ammonia removalStartup of biological phosphorus removal system

variation of Modified JohannesburgA-A-O process not as efficient

Questions?

Leon Downing, Ph.D.leon.downing@freese.com

(817) 735-7305

David R. Jackson, P.E., BCEEdrj@freese.com(214) 217-2257