Wastewater treatment in a hybrid biological reactor (HBR): effect of organic loading rates

A novel hybrid biological reactor which contained both suspended- and attac hed-growth biomass was developed by introducing porous materials into a reg ular activated sludge unit and used for the treatment of domestic wastewate r. The development of suspended- and attached-growth biomass in this reacto r and the effect of the organic loading rates (OLR) on the operational perf ormance were investigated. SEM observation revealed three different pattern s of biomass immobilization in carriers, micro-granules mechanically retain ing in the polyurethane foam pores, small multi-cellular structures attachi ng to the inner polyurethane surface and individual microbial cells attachi ng on the polyurethane surface. The total biomass concentration in hybrid r eactors increased to 4.30-5.75 g/l when the volumetric portion of the carri er was 15-30%. The concentration of attached-biomass increased with increas e of OLR, moreover, the biomass fixed in the carriers predominated in the r eactor at all OLR applied in this study, suggesting that the attached-bioma ss played a major role in COD removal. (C) 2000 Elsevier Science Ltd. All r ights reserved.