CRITICAL FLUX CONCEPT FOR MICROFILTRATION FOULING

Several constant-flux filtration experiments for yeast cell suspension s, yeast cell debris, and dodecane-water emulsion were performed at va rious operating conditions in both hat-sheet and tubular-membrane syst ems. The aim of the paper is two-fold. Firstly the relationship betwee n constant-Aux behaviour and membrane fouling is discussed. In some ca ses constant-flux filtration was realized at a constant transmembrane pressure which was below a critical value. In general constant-flux: f iltration was obtained with moderately increasing transmembrane pressu re, and this approach is shown to have some advantages over normal con stant-pressure filtration because it clearly provides for the possibil ity of avoiding over-fouling and so reduces the severity of fouling. S econdly, the concept of critical flux is introduced. Whilst it has lon g been recognised that low-pressure microfiltration is much more effec tive than high-pressure microfiltration, the emphasis in this work is upon the possible existence of a critical flux and the desirability of starting filtration operations at a low flux. The critical-flux hypot hesis is that on start-up there exists a flux below which a decline of flux with time does not occur. Equations which may enable identificat ion of the appropriate flux level are included.