The MBR technology has evolved rapidly over the past two decades with significant gains in performance and reliability, and reductions of costs. While the MBR process is recognized for providing superior effluent quality in a small footprint, it carries additional operating costs associated with the membrane system, including the periodic replacement of the membranes which have a life shorter than the civil components of the plant. The methodology used to determine membrane life was to analyze the entire data set of ZeeWeed MBR membranes shipped to North American sites over the period of 15 years since their commercial introduction. This analysis shows that membrane life for the current generation product should be greater than 10 years. The analysis also considered the various mechanisms of aging and end-of-life triggers. It was determined that a slow increase in operating pressure and the need for more frequent chemical cleaning should be the dominant end-of-life trigger with the current product. The most effective method for membrane replacement is a planned campaign where a fixed portion of the plant, typically dictated by the membrane train configuration, is replaced on an annual basis in the period of time around the anticipated life of the membranes. (C) 2012 Elsevier B.V. All rights reserved.