IFAS Process: A truly Hybrid process bringing benefits of both suspended and attached growth process together
Conventionally with a floating attached growth process, MBBR (Moving Bed Bio Reactor) configuration is a popular choice. In MBBR no sludge recycling is practiced and all reduction is obtained via biomass attached on the media.
However, over the past few decades, the IFAS (Integrated Fixed Film Activated Sludge) process has gained momentum due to its hybrid configuration and the specific benefits the process provides to 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 to the new plants as well.
How IFAS Process works?
As the title suggests IFAS technology is nothing but an activated sludge process with attached growth media added to the aeration basin. Thus, in the IFAS process, MLSS is kept in the aeration tank just like the conventional activated sludge process, and attached growth media is added to it. This addition of attached growth media in different forms enhances the efficiency of the aeration tank by providing additional biomass in the aeration tank.
Advantages of IFAS Process:
Due to a combination of both attached growth as well as suspended growth-based activated sludge process, the IFAS process provides 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.
- Truly Hybrid process which provides biodegradation through both Suspended as well as Attached biomass.
Due to the presence of biomass both on attached growth media and in the MLSS present in suspension, the IFAS process provides higher volumetric reduction which reduces the wastewater treatment plant footprint 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 in reducing clarifier solids loading as much of the biomass is retained within the reactor on the attached growth media.
- 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, the IFAS process allows the development of a diverse community of microbes responsible for the degradation of a wide range of organic pollutants present in different wastewater generated 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 reduction efficiencies. Under toxic shock load conditions, the diversity of microbial community allows speedy process recovery and thus IFAS process has a much better toxic shock load response compared to conventional technologies.
- Provides a wide range of operating windows for MLSS, F/M ratio and thus makes it the most suitable process configuration for scenarios where there are high seasonal as well as spatial fluctuations in organic and hydraulic loading.
Any wastewater treatment plant receives seasonal and spatial fluctuations of organic loading which requires adjustment of key process parameters of MLSS, FM ratio, and SRT for optimum reduction efficiency 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 the 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 developed in the biological reactor.
- Provides the same flow sheet and operational philosophy as the Conventional Activated Sludge Process and thus allows the useful and effective utilization of existing knowledge of the Activated Sludge Process
Any IFAS process is nothing but a simple activated sludge process with attached growth IFAS media added in it. Thus, it provides the same flow sheet and operational philosophy as the 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 thus improving clarifier performances.
Due to the 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 OPEX associated with any reuse and recycling.
Types of IFAS Media used:
Traditionally IFAS process solutions have been developed using a variety of fixed-in-place types of attached growth media like:
- Ropes
- Textile Curtains
- Flat Sheets made of different plastic materials
However, though these media provide better reduction, 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 the development of nuisance organisms which otherwise deteriorates the reduction. Further, the penetration of substrate to and from the biofilms gets reduced as the thickness of the biofilms increases. This phenomenon further reduces the reduction efficiency for the fixed-in-place type of IFAS media.
Over the past few years, floating MBBR media for biological processes has been developed which helps to overcome these difficulties present in the fixed-in-place type of IFAS media.
Thus, the past few years have seen significant development and application of floating MBBR media for the design and development of the IFAS process.
IFAS or MBBR? Which Process? How to select specific process configuration
When floating media is considered for both the MBBR and IFAS processes, it raises a concern whether to select MBBR or IFAS. It is to be noted that when floating media is used, the IFAS process is nothing but the MBBR process with sludge recycle to maintain MLSS in the suspended phase.
However, there are certain specific points one can consider while selecting the MBBR or IFAS process for their wastewater treatment requirement.
While designing an MBBR process using plastic media, it is generally assumed that reduction efficiencies are the result of the biomass present on the media and thus virtually there is no reduction from the biomass detached from the media.
When an MBBR process is designed for a short HRT for an application like BOD reduction only, then this general design assumption might be valid. Thus, applying an MBBR process with plastic media for simple a low-loaded BOD reduction plant might be useful as it may allow a simplified process with no sludge recycle. Such standalone MBBR may also allow the application of clarification units like lamella or DAF for solids separation.
Application of MBBR Technology
- BOD reduction requires shorter HRTs.
- Space is restrained for conventional clarifiers or where chemical addition in the solid’s separation step is permissible.
Fig. 2 Once through MBBR application for BOD COD reduction at short HRT
However, for certain industrial applications where the overall HRTs requirement for pollutant reduction is higher due to inherent properties of the effluent, the assumption of MBBR design that there is no reduction from the suspended biomass present in the reactor doesn’t stand valid. When HRTs are large enough, it is also advisable to exploit the reduction efficiencies of the suspended phase by maintaining certain levels of MLSS in the suspended phase.
Thus, for industrial effluents where the MBBR process has a much higher HRT requirement, shifting to the IFAS process and running the floating media-based reactors with IFAS process configuration helps reduce the footprint further because volumetric reduction efficiencies are increased due to higher reduction from both suspended and attached growth phase.
In cases when ammonia nitrogen is required to be removed from wastewater, the application of MBBR has certain disadvantages. Due to once thorough process, the 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 substrates like ethanol or methanol is a must for Anoxic MBBR. Moreover, when Bio-P reduction is required, the MBBR process is not much helpful because micro-organisms responsible for Bio-P reduction can not be fixed on biofilms thus maintaining them in suspension is a must which requires sludge recycle and thus in such a scenario IFAS process is more suitable.
Disadvantages of MBBR Process
- Anoxic Denitrification reactor requires media addition which further requires additional mixing arrangement and addition of ready food for denitrification bacteria.
- Bio-P reduction is not feasible with MBBR process configuration as there is no sludge recycling and thus maintaining biomass for Bio-P uptake is not possible.
IFAS : An Ideal Process Configuration for Industrial Effluents, Biological Nutrient Reduction (BNR) and Bio-P Reduction
While IFAS process which is a hybrid process configuration, provides distinct advantages over the conventional MBBR process for applications such as the treatment of industrial effluents and biological nutrient reduction requiring nitrification, denitrification, and Bio-P reduction processes.
Advantages of IFAS Process over MBBR Process:
- IFAS process allows higher volumetric reduction efficiencies compared to once through the MBBR system due to reduction obtained both in the suspended and attached growth phase. This higher volumetric loading results in a lower footprint of industrial effluents requiring large HRTs.
- For the Ammonia Nitrogen reduction process, the Denitrification process can be designed with suspended biomass and without the addition of any MBBR media or readily available substrate for denitrification.
- IFAS process can be configured for Bio-P reduction with conventional process concepts like A2O or BardenPho process as utilized with activated sludge process.
Application of IFAS Process:
Being a hybrid process, the IFAS process can be virtually applied for all biological wastewater treatment reduction applications. Some of the major applications of the IFAS process can be summarized as below.
- BOD, COD reduction (Carbonaceous matter) reduction from municipal as well as industrial wastewater
- Nitrification and Denitrification for Ammonia reduction from Municipal as well as industrial effluents
- Biological Phosphorus reduction from Municipal and industrial wastewater
- Upgrading any existing suspended growth process-based plant for higher capacity or better reduction efficiencies
Amit Christian is a MSc graduate in Environment Science from Middlesex University, London, UK. He has been active in the field of water and wastewater treatment since 1998. He specializes in the design, engineering, and management of various biological wastewater treatments such as Activated Sludge Process (ASP), Sequencing Batch Reactor (SBR), Moving Bed Bio Reactor (MBBR), and Integrated Fixed Film Activated Sludge (IFAS). He has helped various Industrial and Municipal clients in troubleshooting, and optimizing their biological wastewater treatment processes to achieve the latest Stringent norms for Ammonia Removal.
