ABSTRACT
The biofilm reactors that we have considered in the past two chapters both come under the heading of fixed media bioreactors in which the media stays in one position as the wastewater flows past. As wastewater flows down through a packed tower, the biofilm grows attached to a solid support that is either stacked or dumped into place, removing the soluble substrate as it does so. Careful selection of the hydraulic and organic loadings is required to ensure that sufficient shear occurs relative to growth to prevent the interstitial spaces in the media from plugging, causing the system to fail. In addition, any suspended solids applied to the tower must be sufficiently small to allow them to pass through those spaces without being trapped, because entrapment would lead to plugging. Likewise, in a rotating disk reactor, the rotational speed must be selected to ensure sufficient shear to prevent the biofilm from bridging the spaces between the disks, thereby blocking contact of the wastewater with the biofilm. Furthermore, as with the packed tower, care must be exercised concerning the admission of suspended solids.
