A practical method to obtain optimum design parameters of vertically mounted submerged hollow fiber module was demonstrated to minimize the energy consumption for aeration. Assuming maximum allowable pressure difference in both ends of hollow fiber membrane was 5%, maximum allowable fiber length was calculated for various fluxes and fiber diameters. In case there was no limitation in fiber length, permeate throughput from unit footprint simply increased with fiber diameter. However, if there was a limitation in fiber length/water depth, optimum range of fiber length and lumen diameter existed. For one-side suction, optimum range of outer fiber diameter and fiber length were estimated to be 2.26-3.25 turn and 1.01-1.90 in, respectively, when operating flux was 20-501/m(2) h and a ratio of lumen and outer diameter was 1:2. In the case of two-side suction, fiber length of 1.01-1.90 m and diameter of 1.34-2.05 mm were the optimum range. Finally, optimum design lines, showing the best combinations of lumen diameter and fiber length, were obtained for one-side and two-side suctions. (C) 2004 Elsevier B.V. All rights reserved.