Integrated Fixed-Film Activated Sludge (IFAS) and Submerged Fixed Film (SFF) are popular wastewater treatment processes for both industrial and municipal treatment applications. Both utilize media carriers to create a protected surface for a biofilm to attach. The large surface area of media carriers can provide capacity for a large biomass inventory, increasing treatment capacity and/or reducing tank volume for treatment. There are two types of media carriers, fixed media and moving media, both of which can be used in IFAS and SFF processes.
In a SFF process, media carriers (either fixed or moving media) are installed in the wastewater tanks. The tanks are aerated to maintain a dissolved oxygen concentration for organic contaminants and nutrients removal. Clarifiers are then used to separate the solids and biomass from the treated wastewater. No sludge recycle with the separated solids and biomass is performed. SFF can also be an anoxic process through the use of submerged mixers that are used to direct the path of the water through the tank. When utilizing moving media, this process is often referred to as Moving Bed Biofilm Reactor (MBBR).
An IFAS process is similar to the SFF process, and either fixed or moving media can be used. The main difference between the two processes is IFAS recycles part of separated biomass from the clarifier to the treatment tanks, which is regularly referred as returned activated sludge (RAS). Therefore, IFAS combines a fixed-film process with an activated sludge process by recycling the sludge back to the aeration tank to increase biomass inventory and treatment capacity. The lack of RAS in a SFF process reduces the load for clarifier solids inventory management.
Both IFAS and SFF can be used for nitrification, denitrification, and BOD removal. Common reasons for choosing one over the other include cost, site space availability, and ease of operation. For example, SFF does not need equipment for recycling activated sludge, so it may make the clarifier easier to operate and maintain. Since IFAS recycles its sludge, it can provide a more efficient usage of tank volume and lower cost on operation and maintenance over time.