A high strength industrial wastewater was treated in a bench-scale activated sludge reactor modified by the addition of biomass support media to the aeration tank. Two experimental biomass support systems (BSS) and one conventional activated sludge system were operated at different mean cell retention times (mixed liquor MCRTs). Three separate media were tested, NOR-PAC and Linpor used as free-floating supports, and BIONET used as a fixed-bed support. The effect of the media on substrate and oxygen utilization, and solid-liquid separation was investigated.

Substantial attached growth did not occur on the NORPAC and BIONET media. The attached biomass concentration in the Linpor systems increased with increased media concentration. The ratio of attached volatile solids to total volatile solids (attached volatile solids + MLVSS) decreased with increased mixed liquor MCRT. The advantages of the BSS would occur at low mixed liquor MCRTs.

Both the BSS and control systems achieved greater than 94% COD removal and substrate utilization rates (mg/h) did not significantly change during the experiments. Therefore, both systems were substrate limited. The substrate limitations caused decreased oxygen uptake rates of the attached biomass with increased mixed liquor MCRT.

The sludge settling of the Linpor systems was a function of mixed liquor MCRT, filamentous upsets, and the presence of the media. Enhanced settling was observed in the Linpor system only at the 3 day mixed liquor MCRT experiment.