Impact of sodium hypochlorite on rejection of non-steroidal anti-inflammatory drugs by biomimetic forward osmosis membranes

Biomimetic forward osmosis membranes with a polyamide-based active layer containing polymersomes incorporating aquaporins were exposed to various free chlorine doses (free chlorine concentration x exposure time) and pH. Membrane chlorination was found to decrease the apolar/polar balance of the membrane surface energy and to increase its negative surface charge density. A substantial modification of the hydrogen-bond network in the membrane active layer was also highlighted. The separation performance of biomimetic membranes was also impacted by chlorine-induced chemical ageing. For the lowest free chlorine doses (100 ppm h), the reverse salt flux was found to increase with respect to the pristine membrane while the water flux dropped by 10–20%. For higher free chlorine doses (1000 and 10 000 ppm h), both the reverse salt flux and the water flux were found higher than for the pristine membrane. These behaviors were explained by the combination of several mechanisms with possible antagonist effects, namely a reduced internal concentration polarization due to ageing of the membrane support material, and modifications of the hydrogen-bond network and surface charge density of the membrane active layer. Although the degradation caused by sodium hypochlorite increased the draw-solute loss per unit of water passed, the biomimetic membranes maintained their rejection ability towards naproxen and diclofenac as rejections higher than 95.9% were measured irrespective of the ageing conditions.