MEMBRANE-SOLUTE AND LIQUID-PARTICLE INTERACTION EFFECTS IN FILTRATION

Solid/liquid separation is concerned with the removal of molecules and molecular aggregates, colloids and particulates from liquids. Interac tion forces can make the separation easier or more difficult. The natu re of the dominant interactions varies according to the type of disper sed phase, and according to the properties (for example, ionic strengt h) of the continuous phase. Traditional approaches to modelling filtra tion processes, and hence to design methodologies, fail to incorporate any of the relevant forces that exist in fine particle separations. H owever, effects of the interactions are interpreted through the use tr aditional approaches combined with experimental data. Future theoretic al developments need to be better based on the fundamentals of solid/l iquid systems. Particle or solute interactions with the separating sur face are important. In cake filtration these determine the ease of cak e discharge, or in crossflow filtration they determine the propensity of a surface to foul. The separating surface can take many forms - wov en textile media, sinters or felts, for example - and can be made from a wide variety of materials, such as polymer films, synthetic or natu rally occurring fibres, metals, ceramics or glass. The paper discusses the general nature of mechanical and thermodynamic interactions betwe en these media and the dispersed phase.