Submerged Aerated Filter (SAF): It is constructed in a very similar way to the BAF plants except that they have a settling tank to clarify the solids that slough from the filter rather than using back-washing. The plant has a 1-4m deep bed of filter media on which to grow a biomass.A blower sends air to the bottom of the bed to provide oxygen for the biomass to support the oxidation process. The air stream promote There are lots of SAF variants;

Combination system

Combination systems have an upstream aerated compartment with a random particulate medium restrained by a mesh across the outlet of the chamber and a downstream chamber which, is also aerated, containing a modular plastic medium.

Loop reactor system

Loop reactor systems feature circular tanks constructed with a central riser pipe with an aerator mounted centrally beneath the pipe. The up flow of air causes the wastewater to flow upwards through the riser pipe and then fall down through the annular space within the tank through a plastic filter medium.

Compartmentalised system

The tank can also be compartmentalised such that the flow of effluent through the tanks is upward through one chamber of medium, downward through the next and so-on. The aerators are positioned at the base of alternate vertical columns of medium to promote the rising and falling columns of wastewater. Recirculation of the effluent is achieved by providing free space at the top and bottom of the reactor beds of medium as both efficient mixing of the effluent and disturbance of any excess solids from the filter medium.