ABSTRACT
The term aerobic solids retention time (aSRT) is sometimes used to account for the actual SRT in the aerobic zone. If the biomass concentration is reasonably uniform throughout the bioreactor, then aSRT is the total SRT times the fraction of bioreactor volume that is aerobic. After the reaction phase, the bioreactor enters a quiescent settling phase to separate and compact the biomass. A new category of reactor is gaining success in the marketplace which uses membranes, rather than gravity settling, to separate the biomass from the treated effluent. With free-floating media, a screen is used to retain the fixed-film matrix within the bioreactor. Bioflocculation seemed to be restricted to aerobic systems because anaerobic systems resisted almost all attempts to form a well-flocculated biomass. High mixed liquor suspended solids concentrations can be maintained which reduces the required bioreactor volume. Suspended growth bioreactors can be used to stabilize residuals produced during waste treatment.
