From ageing analysis to second life: a sustainable approach to osmosis membrane recycling

In this study, constraints appearing during operational membrane life such as the effects of drying, industrial use, and chemical exposure on RO membranes were systematically assessed to better understand their impact on membrane performance and to evaluate whether these factors pose limitations for membrane recycling. Similar approach was also directed to forward osmosis (FO) membranes, an emerging technology with similar composition with polyamide (PA) selective layer coated on a polysulfone (PSf) layer. Results showed that drying significantly reduces membrane permeabilities (65% for new membranes, 55% for SW30-used and 85% for BW30-used). However, after ethanol-soaking, a partial recovery was observed, indicating that the PA layer damage may be reversible to some extent. In contrast, for the PSf layer, drying caused irreversible damage (90% permeability loss for new membranes, 35% for SW30-used and 70% for BW30-used), including surface cracking, leading to a complete loss of functional properties. Industrial use was also evaluated for both PA and PSf layers. The results indicated performance degradation, mainly due to pore compaction in the PSf layer and partial degradation of the PA layer, confirming the impact of long-term use on membrane integrity. The study further examined chemical exposure, using a three-step free chlorine protocol to selectively degrade the PA layer. This process successfully produced nanofiltration (NF)- and ultrafiltration (UF)-like membranes, confirming the feasibility of transforming end-of-life (EoL) RO membranes into membranes with different separation properties. In parallel, the resistance of membranes to extreme pH conditions was tested. While membranes exhibited good resistance at acidic (slightly changes in permeability), neutral and basic pH values, the addition of 10 ppm free chlorine triggered degradation, particularly under neutral and basic conditions