The effect of axial baffles in non-circular channelled membranes on the critical flux has been investigated. Various geometric configurations of inserts, namely cylindrical rod, helical baffles and alternating direction helical baffles have been used. Higher critical fluxes were achieved with most of the inserts. Under the conditions of the present study i.e. at a fixed hydraulic dissipated power, the introduction of alternating direction helical baffles led to the greatest improvements (up to 37.7%). These improvements are ascribed to the turbulence generated and mixing that this encourages within the flow channel. Helical and cylindrical rod inserts produce comparable results which are unexpected and is attributed to the star-shaped flow channel which reduces the effectiveness of the rotational flow field that the helical baffles are thought to produce. In this study, helical baffles having two turns per 25 mm produce optimum flow conditions leading to the best performance in terms of the critical flux in the helical baffle series. An increase in the rod diameter seems to lead to a decrease in the flux enhancement. The results are explained in terms of the hydrodynamics that each axial baffle structure produces and their interaction with the star-shaped channel geometry within the filtration system. (c) 2006 Elsevier B.V. All rights reserved.