Fixed Film

Fixed Film

Fixed Film reactors are bioreactors that part of a larger trickling filter systems containing a septic tank, fixed film reactor, and a clarifier.

Fixed Film

(Copyright Aqua Tech Systems, Fayetteville, AR)

Table of Contents

General Information

Fixed film reactors are used to treat organic hazardous, non-hazardous, and toxic wastes. Hazardous materials in untreated water can be degraded to less dangerous compounds using biological agents such as microorganisms or their products.

Because the microorganisms (“bugs”) multiply every fifteen minutes or so, they must be supplied with large amounts of nutrients and oxygen. The hazardous materials serve as nutrients for the microorganisms.

Equipment Design

The schematic below is a diagram of a typical fixed film reactor. Untreated water enters the tank from the inlet port. The water then flows through three different compartments, each one containing numerous bugs that consume hazardous material. An air diffuser network provides the air the bugs require for growth.

fixed film reactor

(Copyright Brentwood Industries, Inc., Reading, PA)

When the water enters the third compartment it passes through a clarifier that separates any bugs from the treated water. The bugs are then recycled back to the first compartment, and the treated water exits the reactor.

Shown below is a diagram of a fixed film biological reactor with the walls cutout to show the media inside. The larger of the two tanks is known as a Submerged Aerated Filter (SAF) which contains fully submerged media in the presence of co-current aeration. The tank that follows the SAF is a clarifier, described above.

fixed film biological reactor

(Copyright Process Wastewater Technologies LLC, Baltimore, MD)

Usage Examples

Fixed film reactors see much use in water treatment. The fixed film reactor shown on the left is mounted on a trailer so it can be transported from site to site with relative ease. The reactor on the right can be used for biological phosphorus and nitrogen removal.

fixed film reactor

(Pictures copyright Process Wastewater Technologies LLC, Baltimore, MD)


  • Allows for multiple varieties of reactions to occur in the same zone
  • High levels of process stability


  • High operational and construction costs
  • High energy requirements



  • Sam Catalano
  • Kelsey Kaplan