Integrated Fixed Film Activated Sludge (IFAS)
Integrated Fixed Film Activated Sludge (IFAS) process is a state-of-the-art biological process used in treatment of municipal and industrial wastewaters for BOD removal, nitrification and denitrification. The process is a hybrid of suspended growth and fixed-film (attached growth) process and may be viewed as a combination of Activated Sludge and MBBR process. It is simply an Activated Sludge process with submerged but floating plastic media in aeration tank.
The plastic media is usually made of HDPE, polyethylene or polypropylene with specific gravity less than 1.0. In addition to the suspended growth bacteria in the aeration tank, the large surface area of the plastics provide abundant surface for bacterial growth. This increases the overall biomass concentration in the aeration tank enabling it to treat higher loads at lower reactor volume. It is usually assumed that most of the BOD removal is done by the suspended growth bacteria while most of the nitrification is performed by the nitrifiers that grow on the plastic media. Medium or coarse bubble diffusers uniformly placed at the bottom of the reactor maintains a dissolved oxygen (DO) concentration of > 3 mg/L. To retain the media flowing out of the tank, screens are placed on the downstream walls. A clarifier or a DAF is placed downstream of the MBBR tank to separate the biomass and the solids from the wastewater. The concentrated sludge from the clarifier/DAF is recycled to the aeration tank as in an Activated Sludge process.
For denitrification, anoxic IFAS tanks are used. The anoxic tank is similar to aerobic MBBR tank described above except that no oxygen is supplied. The tank contains no diffusers and the media is kept in suspension in the reactor through submersible mixers. Other feature such as the screen is the same as aerobic reactor although the design may be slightly different.
A schematic of the IFAS process for BOD removal and/or nitrification is shown below. Wastewater enters the IFAS reactor where the suspended biomass and the biomass attached to the surface of the media degrades organic matter resulting in BOD removal and/or nitrification depending on the type and characteristic of the wastewater. Organic carbon is converted to carbon dioxide and leaves the system while the ammonia and nitrogen in the organics are converted to nitrates through nitrification process. Oxygen required for the process is provided through the diffusers installed at the bottom of the reactor. The treated wastewater then flows through the screens to the downstream clarifier/DAF where the biomass and solids are separated from the wastewater. The concentrated sludge from the clarifier/DAF is recycled to the aeration tank.
There are hundreds of IFAS installations worldwide. IFAS is used in treating municipal wastewaters and the industrial wastewaters including effluents from food and beverage plants, steel mills, oil refineries, petrochemicals, chemical plants, paper mills and any industries requiring wastewater treatment for BOD removal, nitrification and denitrification. IFAS is widely used for upgrading existing Activated Sludge plants designed for BOD removal only to nitrification and nitrogen removal.