In this paper, an approach for the optimal design and operation of a continuous ultrafiltration installation is presented. The approach is based on a dynamic model which takes into account fouling and cleaning issues and consists of a set of integral, differential and algebraic equations comprising integer and continuous variables. An economic objective function which includes capital and operating costs, is used and appropriate operating constraints are imposed. The overall problem is formulated as a mixed integer dynamic optimisation problem and a solution procedure is proposed. Using this method, a cheese whey ultrafiltration plant involving the use of commercially available tubular ceramic membrane modules, is studied. Using the proposed solution procedure, the optimum number of stages, the number of membrane modules per stage, the feed and circulation pumps sizing, the work pressure profile and the timing of the operating and cleaning tasks, are determined. (C) 2004 Elsevier B.V. All rights reserved.