Critical fouling conditions induced by colloidal surface interaction: from causes to consequences

Critical fouling conditions (CFC) are defined as the process operating conditions leading to the formation of multilayer irreversible fouling at the membrane surface. This irreversible fouling is the result of a phase transition in the accumulated matter from a dispersed phase (concentration polarisation) to a condensed phase (deposit or gel formation): the spinodal decomposition. Properties of concentrated colloid dispersions and their related phase transitions are integrated into a classical filtration mass balance via colloidal osmotic pressure, H. This then allows us to define CFC for both cross-flow and dead-end filtration. These CFC are expressed in terms of critical pairs of operating conditions: the set permeate flux/boundary layer thickness (directly linked to cross-flow velocity) in cross flow and the critical set permeate flux/filtered volume in dead end.