Conventionally with free floating attached growth process, MBBR (Moving Bed Bio Reactor) configuration is a popular choice. In MBBR no sludge recycle is practiced and all removal is obtained via biomass attached on the media only.

However, over the past few decades, IFAS (Integrated Fixed Film Activated Sludge) process is gaining momentum due to its hybrid configuration and specific benefits the process offer to the wastewater treatment plants. IFAS process with textile sheets, cord media and other fixed in place media has been around the scene quite for a long time and has been successfully applied for the upgradation of existing overloaded activated sludge plants.

Though originally developed for the upgradation of existing activated sludge plants, the hybrid process configuration can be applied for the new plants as well.

How IFAS Process works?

As the name suggests IFAS process is nothing but an activated sludge process with attached growth media added to the aeration basin.  Thus, in IFAS process, MLSS is maintained in the aeration tank just like conventional activated sludge process and attached growth media is added to it. This addition of attached growth media in different forms enhance the performance of the aeration tank by providing additional biomass in the aeration tank.

ifas process
Fig 1: Working of IFAS process

Advantages of IFAS Process:

Due to a combination of both attached growth as well as suspended growth based activated sludge process, IFAS process offers distinct advantages compared to stand alone attached growth or activated sludge process alone.

    • Truly Hybrid process which provides biodegradation through both Suspended as well as Attached biomass

Due to presence of biomass both on attached growth media and in the MLSS present in suspension, IFAS process provides biodegradation of wastewater through both mode of removal resulting in higher volumetric removal rates which reduces the wastewater treatment plant foot print significantly.

    • Help reduces clarifier solids loading rates as much of the biomass is retained within the reactor on Attached growth media.

As a lot of active biomass fraction is retained on the attached growth media added to the IFAS reactor, the IFAS process configuration helps reduce the solids loading rate of clarifier as only the suspended biomass or MLSS is going to the clarifier for settling.

    • Provides development of diverse microbial community structure which improves the process performance enhancing toxic and shock load response of the process.

Because of its hybrid nature, IFAS process allows development of a diverse community of microbes responsible for the degradation of a wide range of organic pollutants present in different wastewater generating from both industries as well as municipalities. Due to biofilm formation on attached growth IFAS media, retention of poorly flocculating biomass in the biological reactor is feasible which allows for improved removal efficiencies. Under toxic shock load conditions, the diversity of microbial community allows speedy process recovery and thus IFAS process has much better toxic shock load response compared to conventional technologies.

    • Offers a wide range of operating window in terms of MLSS, F/M ratio and thus makes it most suitable process configuration for scenarios where there is high seasonal as well as spatial fluctuations in organic and hydraulic loading rates.

Any wastewater treatment plant receives a seasonal and spatial fluctuations of organic loading which requires adjustment of key process parameters of MLSS, FM ratio and SRT for optimum removal rates and better biomass settling properties. In a conventional activated sludge process which receives a high level of seasonal fluctuations, maintaining these parameters may become difficult.      

However, as IFAS process allows retention of biomass both in suspension as well as on IFAS media, by varying the MLSS as well as attachment/detachment of biomass from the IFAS media, a wide range of MLSS, F/M ratio conditions can be maintained in the biological reactor.

    • Offers same flow sheet and operational philosophy as Conventional Activated Sludge Process and thus allows the useful and effective utilization of existing knowledge of Activated Sludge Process

Any IFAS process is nothing but simple activated sludge process with attached growth IFAS media added in it. Thus , it offers the same flow sheet and operational philosophy as conventional activated sludge process. Any process engineer or plant operator having reasonable knowledge of activated sludge can operate the IFAS process without any specialized process knowledge.

    • Improves Settling Properties of Sludge with lower SVI values and thus improving clarifier performances.

Due to diversity of microbial community within the IFAS reactor, sludge settling properties are improved drastically with lower SVI values and better clarity of the treated effluents. This results in a much lower post treatment costs associated with any reuse and recycle.

Types of IFAS Media used:

Traditionally IFAS process solutions have been developed using variety of fixed in place type of attached growth media like:

  • Ropes
  • Textile Curtains
  • Flat Sheets made of different plastic materials

However, though these media provide better performance, due to its stationary position in the aeration tanks, at times they face excessive biomass growth on it. Once the biomass growth becomes too thick, it causes development of nuisance organisms which otherwise deteriorates the performance. Further the penetration of substrate to and from the biofilms gets reduced as thickness of the biofilms increases. This phenomenon further reduces the removal rates for fixed in place type of IFAS media.

Over the past few years, free floating MBBR media for biological process has been developed which helps to overcome these difficulties present in the fixed in place type of IFAS media.

Thus, past few years have seen a significant development and application of free floating MBBR media for the design and development of IFAS process.

IFAS or MBBR? Which process? How to select specific process configuration

When free floating media is considered for both MBBR and IFAS process, it raises a concern whether to select MBBR or IFAS. It is to be noted that when free floating media is used, IFAS process is nothing but MBBR process with sludge recycle to maintain MLSS in the suspended phase.

However, there are certain specific points one can consider while selecting MBBR or IFAS process for their wastewater treatment requirement.

While designing an MBBR process using plastic media, it is generally assumed that all the removal efficiencies are result of the biomass present on the media only and thus virtually there is no removal from the biomass detached from the media.

When a MBBR process designed for a short HRT for an application like BOD removal only, then this general design assumption might be valid. Thus, applying a MBBR process with plastic media for simple a low loaded BOD removal plant might be useful as it may allow a simplified process with no sludge recycle. Such standalone MBBR may also allow application of clarification units like lamella or DAF for solids separation.

Application of MBBR process

  • BOD removal requiring shorter HRTs
  • Space is restraint for conventional clarifiers or where chemical addition in the solids separation step is permissible
Fig 2: Once through MBBR application for BOD/COD removal at short HRT

However, for certain industrial application where the overall HRTs requirement for the pollutant removal is higher due to inherent properties of the effluent, the assumption of MBBR design that there is no removal from the suspended biomass present in the reactor doesn’t stand valid. When HRTs are large enough, it is also advisable to exploit the removal efficiencies of suspended phase by maintaining certain levels of MLSS in the suspended phase.

Thus for industrial effluents where MBBR process has much higher HRT requirement, shifting to IFAS process and running the free floating media based reactors with IFAS process configuration helps reduce the foot print further because volumetric removal efficiencies are increased due to higher removal rates from both suspended and attached growth phase.

In cases when ammonia nitrogen is required to remove from wastewater, application of MBBR has certain disadvantages. Due to once through process, MBBR process with Denitrification application requires Anoxic reactors with attached growth media for denitrification. Under anoxic conditions as air can not be employed for agitation and mixing, special mixing equipment requirement makes the application of MBBR media in Anoxic reactors quite costly. 

Further, due to denitrifying bacteria growing on the media, the substrate gradient for BOD penetration is difficult to maintain and adding denitrification substrate like ethanol or methanol is must for Anoxic MBBR. Moreover, when Bio-P removal is required, MBBR process is not much helpful because micro-organisms responsible for Bio-P removal can not be fixed on biofilms and thus maintaining them in suspension is must which require sludge recycle and thus in such scenario IFAS process is more suitable.

Fig 3. Typical Nitrogen Removal MBBR with Chemical P removal

Disadvantages of MBBR process application in Ammonia / Nitrogen removal and Bio-P removal

  • Anoxic Denitrification reactor requires media addition which further requires additional mixing arrangement and addition of ready food for denitrification bacteria
  • Bio-P removal is not feasible with MBBR process configuration as there is no sludge recycle and thus maintaining biomass for Bio-P uptake is not possible.

IFAS Process: An Ideal process configuration for industrial effluents, Biological Nutrient removal (BNR) and Bio-P removal:

While IFAS process which is a hybrid process configuration, offers distinct advantages over conventional MBBR process for applications such as treatment of industrial effluents and biological nutrient removal requiring nitrification, denitrification and Bio-P removal processes.

Fig 4: Typical A2O process configuration with IFAS process for Bio-P and Nitrogen Removal

Advantages of IFAS process over MBBR process:

  • IFAS process allows higher volumetric removal efficiencies compared to once through MBBR system due to removal rates obtained both in suspended and attached growth phase. This higher volumetric loading results in lower foot print of industrial effluents requiring large HRTs.
  • For Ammonia Nitrogen removal process, Denitrification process can be designed with suspended biomass and without addition of any MBBR media or readily available substrate for denitrification.
  • IFAS process can be configured for Bio-P removal with conventional process concepts like A2O or BardenPho process as utilized with activated sludge process

Application of IFAS process:

Being a hybrid process, IFAS process can be virtually applied for all biological wastewater treatment removal application. Some of the major applications of IFAS process can be summarized as below.

  • BOD , COD removal (Carbonaceous matter) removal from municipal as well as industrial wastewater
  • Nitrification and Denitrification for Ammonia removal from Municipal as well as industrial effluents
  • Biological Phosphorus removal from Municipal and industrial wastewater
  • Upgradation any existing suspended growth process based plant for higher capacity or better removal efficiencies

Speak with Expert on LinkedIn

Amit Christian, having MSc degree in Environmental Science from UK university has more than 20 years of experience in the field of water and wastewater treatment. He has expertise in MBBR and IFAS process design, engineering and process start up /commissioning.