Filtration performance and pore size distribution of hypochlorite aged PES/PVP ultrafiltration membranes

• Effect of membrane ageing on model solute filtration was studied.
• Modifications in membrane characteristics were correlated with selectivity evolution.
• Membrane degradation has an effect on solute–membrane interaction and lowered selectivity.
• Scenarios of pore size distribution evolution over degradation process were proposed.

The objective of the present work is to correlate the evolution of membrane characteristics due to contact with hypochlorite used as cleaning agent to its selectivity towards model solutes. Accelerated ageing experiments were performed by soaking the membrane at ambient temperature in hypochlorite solutions. The total free chlorine concentration of these solutions was fixed at 350 ppm and the pH at 8. The model solute selected was T500 Dextran. The experimental results demonstrated that hypochlorite induced membrane degradation, on one hand modified the solutes–membrane interactions increasing irreversible fouling and, on the other hand, lowered the selectivity. These results have been correlated with the modification of the pore size distribution following a protocol in which fouling did not affect membrane characterization. The most probable scenario of distribution evolution over degradation process was an increase of the pore radius of the initial population, accompanied by a decrease in their number, coupled with the appearance of defects, whose radius increased with the progress of the degradation.