Effects of hypochlorite exposure on flux through polyethersulphone ultrafiltration membranes

Polyethersulphone ultrafiltration membranes with a nominal molecular weight cut off of 10 kDa were degraded in solutions of sodium hypochlorite over a range of pH values at 55 °C to achieve exposure measured in ppm-days of chlorine exposure. The degraded membranes were tested, using an ÄKTAcrossflow™ system, for clean water flux, demineralised whey flux and protein rejection. The water fluxes for three membranes (new, 10,000 ppm-day pH 12, and 10,000 ppm-day pH 9) were found to be about 100, 200 and 400 L m−2 h−1, respectively with cross flow at 1 bar transmembrane pressure. However whey fluxes were about 23, 5, and 6 L m−2 h−1 for the same three membranes. Size exclusion chromatography of the permeates showed significant permeation of α-lactalbumin and β-lactoglobulin through membranes degraded at pH 9 for 20,000 ppm-days, while almost no permeation was found for degradation at pH 12.These results show that hypochlorite degradation affected fluxes by at least two mechanisms. It was likely that membrane pitting increased the pore size causing increased water flux and reduced protein rejection. However hypochlorite also seemed to alter the membrane surface properties, causing the protein to form a less permeable layer that reduced the flux of whey.

Research highlights▶ The water flux through polyethersulphone increased, but whey flux decreased, after exposure to sodium hypochlorite solutions. ▶ The rejection of whey protein decreased after exposure to sodium hypochlorite solutions. ▶ This showed that hypochlorite has an effect of PES membranes other than enlargement of pores.