Fig. 4. Stage-based recycling of EOL composite membranes in practical applications and performance evaluation of the recycled membranes.

(A) Depolymerization performance of EOL membranes under varying fouling conditions. The tested foulants included bovine serum albumin (BSA), sodium alginate (SA), humic acid (HA), and gypsum, each applied at two concentrations (0.5 and 1.0% by weight relative to the membrane, top) to simulate mild and severe fouling conditions, respectively. The mild fouling condition (i.e., blue columns at the bottom) had a negligible impact on PET substrate depolymerization, with the largest decrease of 9% in BHET yield observed for gypsum. The severe fouling condition (i.e., red columns at the bottom) exhibited a slightly more pronounced effect, with SA causing a maximum yield reduction of ~20%. Notably, these reductions in BHET yield could be fully restored by extending reaction time to 60 min (striped bar, data provided in table S8). (B) Process flow of stage-based recycling EOL membranes from real-world membrane modules. Digital photos and scanning electron microscopy images of both membrane module, EOL membranes, and recycled membranes are also illustrated. (C) Molecular weight cutoff (MWCO) test comparing separation performance of recycled and commercial UF membranes. MWCO is as the molecular weight at which 90% of the solute is rejected. (D) Mechanical properties of the recycled RO membrane and the commercial RO membrane. (E) Water permeance and NaCl rejection of the recycled RO membrane compared with the commercial RO membrane.