Experimental evaluation of nanoplastics fouling behavior on ultrafiltration membranes using optical coherence tomography (OCT)

Abstract

Ultrafiltration membranes find widespread use in water treatment but suffer from performance losses due to fouling. This study investigates the fouling behaviors of commercial polyethersulfone (PES), regenerated cellulose (RC), and recycled PES membranes during the filtration of wastewater containing polystyrene (PS) nanoparticles and a mixture of PS and bovine serum albumin (BSA). Optical coherence tomography (OCT) is used for real-time, in-situ examination of fouling, providing unique insights into nanoplastics-induced fouling formation. Membrane performance was evaluated through flux decline and permeability recovery measurements. Results indicate that nanoparticles form a uniform cake layer, with membrane characteristics such as zeta potential and hydrophobicity influencing fouling reversibility. The RC membrane showed complete permeability recovery after physical cleaning, while hydrophobic interactions hindered recovery for PES membranes. Notably, flux reduction was greater for PES membranes (particularly with a 150 kDa MWCO) during PS filtration and worsened with the combined PS and BSA solution. Using the OCT technique, we observed two distinct types of fouling and their resulting structures: (i) a loose or fluffy-like formation; and (ii) flocs or particle agglomerates. This study also combined OCT with conventional techniques like SEM and CLSM. This knowledge offers guidance for choosing the proper membrane material in water treatment applications