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Wastewater Biological Treatment

Model SRB


The PRO-Equipment ROTOAIR PROCESS provides a simple and effective method of treating organic wastewater in a natural biological process. This process is a combination of submerged, fixed film and suspended growth activated sludge.

Wastewater treatment using ROTOAIR technology is economical and effective because it uses suspended activated sludge in the mixed liquor and fixed microorganisms in a bio-film on the surface of Rotating Contactors. The combination of fixed and suspended biomass allows for much higher equivalent active mass to be maintained with a shorter hydraulic retention time in a smaller tank.

Aeration is achieved solely by the rotation of the fixed film media.

The ROTOAIR CONTACTORS are normally 70% or more sumerged in the wastewater. This increases capacity to supply oxygen to the mixed liquor, increases hydraulic residence time, and reduces the mechanical load on the rotating contactors. The rotating contactors are the sole supplier of air to the entire process. As a result, energy requirements may be half that of conventional activated sludge.

The ROTOAIR PROCESS provides an extremely high degree of treatment in removing BOD, COD, and nitrogen.


  • Simple Construction

  • Small Foot Print

  • Low Power Requirements

  • Low Construction and Installation Cost (option for field assembly in-place)

  • Minimum Head Loss

  • Minimum Need for D.O. Control and Solids Return

  • High Tolerance to Wastewater Load Fluctuations

  • Improved Sludge Characteristics


The ROTOAIR rotating contactor supports a viable biomass and serves as an aerator. Contactor media are contained in a slotted housing, which captures and transfers air and mixed liquor as it rotates. The rotating contactor is submerged to over 70% if it’s radius.

On the rising side, mixed liquor is lifted in the housing, and then drained back through a bottom slot as it rotates in the air arc. This provides additional aeration of mixed liquor. When entering the mixed liquor on the down side, captured air is released through the upper slot as it approaches bottom center. This forms medium to fine bubbles, which provide further mixing, biomass control on the fixed surface, and supply of dissolved oxygen to the mixed liquor.

In this manner, both the fixed biological film and mixed liquor solids are supplied with sufficient oxygen to sustain aerobic conditions.

A special feature of the ROTOAIR contactor design is the absence of media in the central 30% region near the shaft where earlier conventional rotating contactors were prone to stagnant, anaerobic conditions.

The ROTOAIR contactor media are symmetrically and radially arranged around the outer periphery of the contactor. Each disc is built of corrugated profile panels to provide maximum bio-growth surface and air chambers. The discs are made of high density polypropylene (HDPP) and are resistant to corrosive liquids and ultraviolet degradation.