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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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MONTH
INFL
UE
NT
CB
OD
(mg/
L)
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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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Month
EFF
LU
EN
T (m
gN/L
7 per. Mov. Avg. (Effluent)
0
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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
)
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EFF
LU
EN
T P
HO
SPH
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(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, [email protected]
(817) 735-7305
David R. Jackson, P.E., [email protected](214) 217-2257