The effects of polyurethane sponge size and type on the performance of an up-flow sponge bioreactor were studied using different sponge cube sizes (1 x 1 x 1 cm, 2 x 2 x 2 cm and 3 x 3 x 3 cm) and types of sponge (S28-30/45R, S28-30/60R, S28-30/80R and S28-30/90R). The reactors were operated under anaerobic conditions in an early stage and an aerobic condition in a latter stage. The results indicate that there was no significant difference in the organic and nutrient removal rates between sponge types. The medium size sponge (2 x 2 x 2 cm) had the best performance in terms of both biomass growth and pollutants removal. Under anaerobic condition, the COD, TN and TP removal efficiencies were up to 70%, 45% and 55%, respectively, and significantly improved under aerobic conditions (e.g. >90% TOC, 95% COD, 65% TN and 90% TP). The external biomass grew faster under anaerobic conditions while internal biomass was dominant under aerobic condition. (C) 2009 Elsevier Ltd. All rights reserved.