The step by step technique was used to determine the critical flux of non-circular multi-channel ceramic membranes under various operating conditions (crossflow velocities, surfactant content, coagulant content, valency, pH and ionic strength) using TiO2 suspensions. It is shown that the non-circular geometry gives rise to a very high critical flux under turbulent flow conditions whilst the opposite effect is observed under laminar flow conditions. The impact of surfactant and coagulant additions on critical flux is also considered. Addition of surfactant decreases the critical flux whilst in contrast, coagulant addition results in a higher critical flux. All the various observations are explained in terms of the hydrodynamics and particle interactions involved within the filtration system. © 2005 Elsevier B.V. All rights reserved.