Unified theory of filamentous activated sludge bulking

Abstract

Filamentous microorganisms play an important role in determining the physical properties of activated sludge. The outgrowth of filaments from activated sludge flocs occurs when conditions within the floc interior allow for a higher growth rate for filamentous microorganisms than for zoogleal microorganisms. One of the common limiting conditions is floc interior dissolved oxygen. Activated sludge zone settling velocity compact volume and sludge volume index can be related to the total length of filaments in a milliliter of sludge. A filament length of 10/sup 7/ microns per milliliter is a good dividing point between a filamentous bulking sludge and a nonbulking sludge. Control of activated sludge bulking by toxic chemicals (chlorine and hydrogen peroxide) can be interpreted in terms of destruction of exposed filaments. Overdosing of toxicant destroy all filaments, and produces a turbid effluent and a floc with no filament backbone. The critical dissolved oxygen level to prevent bulking varies with factors such as waste character and strength, reactor configuration and aeration system, and temperature.