FLUX PATTERN AND FOULING OF MEMBRANES DURING ULTRAFILTRATION OF SOME DAIRY-PRODUCTS

The flux pattern of milk (whole milk, skimmed milk and buttermilk) sho wed a distinct contrast to whey (sweet whey and acid casein whey) syst ems during ultrafiltration (UF) at constant composition. For milk syst ems, the initial flux was lower than for whey systems, but the flux st abilised within a few minutes of operation. However, for both acid and sweet whey, the flux continued to fall with time for nearly 1 h. The fouling coefficient (FC) for buttermilk was 0.6 after 5 min, rising to 0.68 after 60 min. During this time flux did not decline, suggesting that concentration polarisation (CP), rather than fouling, was control ling the flux rate. In contrast, the FC for whey was 0.5 after 5 min w ith a progressive rise over the next 55 min, but the flux also fell th roughout this period suggesting that flux was controlled by fouling ra ther than CP. The higher concentration of protein in milk systems appe ared to be responsible for CP, rather than fouling, being the controll ing mechanism.