A submerged MBR with a pure oxygen system was operated at high COD loading conditions to find out how high a level of COD loading can be treated consistently in an aerobic condition. Pure oxygen was supplied with circulated MLSS to the aerobic tank by a two-phase nozzle to increase oxygen transfer efficiency. Tested COD loadings ranged from 2 to 10 kgCOD/m(3) day. And the effect of MLSS concentration on the membrane fouling was investigated from 5000 to 25,000 mg/L. The membrane fouling rates and filtration resistance were tested to evaluate the effect of COD loadings and MLSS concentrations. Over the range of COD loading tested (2.0-10 kgCOD/m(3) day), the effluent qualities ranged from 35 to 69 mg/L and the COD removals ranged from 99.1 to 99.7 for synthetic wastewater. The membrane fouling rates increased seven-fold over a five-fold increase in COD loadings. And the fouling rates increased almost nine-fold over a three-fold increase in MLSS concentration. The membrane fouling in high COD loading conditions was more sensitive to MLSS concentration than COD loading. The specific EPS productions in this test ranged from 6.9 to 10.9 mgEPS/gVSS, and the specific polysaccharide and protein productions were 92 mgPolysaccharide/gVSS and 1.8 mgProtein/gVSS, respectively. (C) 2012 Elsevier B.V. All rights reserved.