Ultrafiltration membranes from waste PET bottles: Effects of PVP and PEG on membrane characteristics and laundry greywater treatment performance

The fabrication of ultrafiltration (UF) membranes from waste polyethylene terephthalate (PET) bottles has attracted increasing attention for wastewater treatment; however, the effects of PET concentration and hydrophilic additives, polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG), on the characteristics and performance of waste PET-based membranes have not been sufficiently investigated. Moreover, the application of waste PET-based membranes for domestic laundry greywater treatment has received limited attention. This study aimed to fabricate waste PET-based UF flat-sheet membranes containing 18 and 20 wt% PET with PVP or PEG (2 and 5 wt%) via the non-solvent-induced phase separation (NIPS) method and to evaluate their performance. Hansen Solubility Parameters confirmed the compatibility of phenol with PET, PVP, and PEG, while water exhibited suitable non-solvent characteristics for the controlled formation of membranes. The fabricated membranes exhibited thicknesses of 0.053 ± 0.009–0.106 ± 0.005 mm, porosities of 70.8 ± 0.2–74.2 ± 0.4%, mean pore sizes of 0.0728 ± 0.0004–0.0766 ± 0.0002 μm, surface roughness (Ra) values of 26.89–63.33 nm, and contact angles of 42–109.83°. Increasing the PET content improved membrane structural integrity. Compared with PVP incorporation, PEG incorporation led to membranes with smoother surfaces, higher hydrophilicity and porosity, greater flexibility, and lower dimensional shrinkage during hot-water exposure. The PET20-PEG5 membrane exhibited the best overall performance, with pure water and greywater fluxes of 142.8 ± 5.5 and 105.2 ± 2.3 L/m².h, respectively, under a vacuum pressure of −85 kPa. The PET20-PEG5 membrane exhibited flux recovery ratios (FRR) of 92.58%, 89.8%, and 88.4% (average FRR: 90.3%) after three fouling-cleaning cycles. PET20-PEG5 membrane achieved removal efficiencies of 99.8 ± 0.18% for TSS, 98.2 ± 0.64% for turbidity, and 69.4 ± 0.42% for COD.