IFAS Technology
Integrated Fixed-Film Activated Sludge — combining suspended growth and biofilm in a single tank to increase capacity 50–100% within the existing plant footprint
Overview
What is IFAS Technology?
Integrated Fixed-Film Activated Sludge (IFAS) is a hybrid biological treatment technology that adds fixed-film carrier media to an existing activated sludge aeration tank, creating a dual-biomass system where both suspended biomass (floc) and attached biomass (biofilm on media) contribute simultaneously to organic matter removal and nitrification. This combination achieves treatment performance and plant capacity that neither process alone could deliver in the same tank volume.
The practical significance of IFAS lies in its ability to increase the treatment capacity of existing activated sludge plants by 50–100% without constructing new aeration tanks. For plant operators facing population growth, tightening discharge consents, or increased industrial load, IFAS retrofit is frequently the most cost-effective upgrade path — the carrier media is simply added to the existing tank, the aeration and clarification systems are retained, and biological capacity is immediately enhanced by the biofilm that establishes on the media within weeks.
In IFAS systems, slow-growing nitrifying bacteria — which are easily washed out of conventional activated sludge systems during storm flows or high-load events — colonize and thrive in the protected interior surfaces of the carrier media. This biofilm-protected nitrifier population provides stable ammonia removal even under conditions that would disrupt conventional activated sludge nitrification, improving compliance reliability significantly.
Process
How IFAS Works
Carrier Media Addition
High-surface-area plastic carrier media is added to the existing aeration tank, typically filling 25–50% of the tank volume. The media is retained in the tank by coarse screens at the outlet, while mixed liquor (suspended biomass) flows freely past the screens to the clarifier as normal.
Dual Biomass Operation
Both suspended floc (as in conventional activated sludge) and biofilm on the carrier media treat the wastewater simultaneously. Organic matter, ammonia, and nutrients are consumed by both biomass populations, with each contributing according to the local substrate concentration.
Biofilm Protection of Slow-Growing Organisms
Nitrifying bacteria, which grow slowly and are vulnerable to washout in conventional systems, colonize the protected internal surfaces of the carrier media. The biofilm environment allows these organisms to maintain long effective sludge retention times (SRT) even when the overall system HRT is short.
Clarification & Sludge Return
Mixed liquor exits through the retention screen to the secondary clarifier as in a conventional activated sludge process. Return activated sludge (RAS) is recycled from the clarifier to the aeration tank as normal. The carrier media remains in the aeration tank throughout.
Benefits
Key Advantages
- Increases existing plant capacity by 50–100% without constructing new aeration tanks
- Lower capital cost than building new treatment capacity — uses existing civil structures
- Biofilm protects nitrifying bacteria from washout — more stable ammonia removal
- Improved resistance to shock loads, temperature changes, and flow variations
- Can be added to operational plants with minimal downtime
- Suitable for both BOD removal enhancement and nitrification improvement
- Reduces the risk of consent non-compliance when plant load increases
- High-surface-area media supports dense biofilm population for compact treatment
Applications
Industries & Use Cases
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