A MLMBR and a conventional IMBR with DO control system were investigated for simultaneously removing organic carbon and nitrogen in the low-strengthen complex wastewater. Four stages of the laboratory scale system with SRT of 30 day and HRTs of 20, 16, 12, and 8 h, respectively, were conducted. During the 4 months experimental period, COD removal efficiencies averaged at 92.2% and 85.3%. SS removal efficiencies averaged at 93.8% and 85.2%, and NH4+-N removal efficiencies averaged at 84.1% and 65.3%, respectively, for MLMBR and IMBR. What's more, the sludge characteristics were explored explicitly, results demonstrate that MLMBR not only perform better in substrates removal, also can alleviate the membrane fouling due to better sludge characteristics. In addition, mathematical statistical models, built on the linear regression techniques were developed for explore the inner relationship between HRTs and the performance of the MLMBR. (C) 2012 Elsevier Ltd. All rights reserved.