The principle of this process is biomass fixing on supports (discs, rolls, trapezoid elements) made out of synthetic material (polystyrene, PVC, etc.) and having maximal exchange surface.

These biological supports are installed on a horizontal axis and are half immersed in wastewater.

The axis is rotated and the bacteriae forming the biomass successively pass from a nutrition phase to an aeration phase.

The biomass in excess is detached from the support and is carried away by the wastewater flow.

The separation of these elements is performed in a clarifier (or settling tank) where the biomass, which density is higher as water’s density, will settle at the bottom of the works.

This process is specifically suitable for configuration in which the load variation is significant since the fixed biomass allows quicker reactivation of biology than in a standard activated sludge.

The field of application of this process is positioned in small station sizes (<5000 IE).