Low fouling conditions in dead-end filtration: Evidence for a critical filtered volume and interpretation using critical osmotic pressure

This paper presents experiments showing the existence of a critical filtered volume (CFV) when operating colloid dead-end filtration. The CFV is here defined as the filtered volume below which there is no irreversible (with respect to a break in the filtration) fouling on the membrane surface: it has thus the same meaning as cross-flow critical flux but applied to a dead-end process. The existence of the CFV is demonstrated when filtering stable latex or clay suspensions in constant-flux filtration experiments with alternating rinses: in contradiction to the current view, an irreversible deposit is not formed as soon as dead-end filtration begins. This critical filtered volume is shown to be dependent on the suspension stability and to be fully linked to the permeate flux: for permeate fluxes of 80 and 1101 h(-1) m(-2) the CFV is, respectively, 82 and 651 m(-2) for latex particles. Analyses of results are made by depicting the transition between concentration polarisation and deposit formation considering a critical osmotic pressure, which appears to be a characteristic of the fouling potential of a suspension. The results are discussed in the light of how this concept could lead to an interesting way to control and develop a strategy to operate filtration in dead-end mode. (c) 2005 Elsevier B.V. All rights reserved.