Despite the potentially important effect of temperature on membrane fouling, very few investigations have been conducted on full-scale membrane bioreactors (MBRs) regarding seasonal variation of fouling. In this study, fouling behavior in a full-scale MBR (capacity 60,000 m(3)/d) in northern China was monitored for a whole year. As the mixed liquor temperature dropped from 27 to 13 degrees C, the Filtration resistance increased from 0.6 x 10(13) to 2.6 x 10(13) m(-1), which was attributable to higher concentration of supernatant organics at lower temperatures. Humic substances were the predominant supernatant organics (10-25 mg/L) in comparison with polysaccharides and proteins (both 5-15 mg/L). The dependence of seasonal supernatant fouling potential on hydrophilic/hydrophobic composition and molecular weight distribution of the organics were analyzed based on statistical correlation. Humic substances in all hydrophobicity and molecular weight ranges correlated closely with the fouling potential. Hydrophilic polysaccharides and large-molecular-weight proteins were also found to contribute to the fouling potential. (C) 2013 Elsevier B.V. All rights reserved