The treatment of a refinery wastewater (oily stream) was investigated using a submerged membrane bioreactor (SMBR) operating with constant permeate flux. During the operation, long-term high organic loading rates were applied in the SMBR by feeding blends of the oily stream with a high strength phenolic wastewater, also generated in petroleum refineries. The effects of high organic loadings were evaluated regarding the organic matter and phenols removal efficiencies. The influence of the loading rate on filtration was also assessed, including the effects on the production of soluble microbial products, namely polysaccharides and proteins, and retention of these compounds by the membrane. The membrane had a key role in the process, since it improved COD and TOC removal efficiencies by 17 and 20%, respectively. The results proved the ability of the SMBIZ to tackle with high strength feed during long-term exposition achieving high phenols removal efficiencies, even with such complex feed. (c) 2008 Elsevier B.V. All rights reserved.