Combining the robust MBBR capabilities with Activated Sludge polishing. The AGAR FFAST (Fixed Film Activated Sludge Treatment) configuration combines the advantages of both fixed-film and suspended biomass technologies. In this configuration, the wastewater is treated first in an MBBR reactor (see above), then in a conventional activated sludge process.
Wastewater is introduced into a single-stage roughing filter, with no sludge circulation. Following this treatment, soluble BOD in the wastewater is reduced by 45%-70% before entering the activated sludge process. The activated sludge system is considerably smaller, as it is required to deal with only a fraction of the organic load of an equivalent conventional plant; in effect, it acts to polish the RF effluent to extremely high qualities.
Return Activated Sludge (RAS) from the secondary clarifiers is recirculated to the beginning of the activated sludge tank; provisions may be made for allowing a part of the RAS to return upstream to the MBBR, thereby creating a selector effect for control of filamentous organisms.
The FFAST process is optimal for plants with limited area, which require consistently high quality effluents coupled with an ability to withstand shock-loads, as well as for new plants or upgrades of high load wastewater treatment plants.