Effective and low-impact backwashing strategies for an ultrafiltration membrane simultaneously fouled by microplastics and organic matter

Global water uncertainty and the prevalence of emerging contaminants in aquatic environments underscore the crucial role of membrane technology in addressing these challenges. Microplastic (MP) pollution is a significant global concern, effectively mitigated by membrane filtration. However, the introduction of MPs into membrane systems can accelerate fouling, particularly when co-existing with other foulants, potentially leading to more complex and severe fouling. This study examines the fouling behavior of MPs and organic matter in a lab-scale ultrafiltration (UF) membrane, evaluates backwashing strategies, and assesses their impacts. The UF membrane achieved 99 % removal efficiency across feed concentrations ranging from 1 to 100 mg-MP/L. Rejected and accumulated MPs within the system intensified fouling, rapidly transitioning from intermediate blocking to cake filtration. Fouling complexity increased when MPs were combined with organic foulants, including pore adsorption. Chemically enhanced backwashing (CEB) with NaOCl was the most effective, providing significant reversible fouling resistance with minimal irreversible fouling. However, NaOCl generated over 100 mu g/L of halogenated by-products and altered the composition of organic matter. Ionic liquid (IL), a green solvent, minimized irreversible fouling but introduced substantial organic residues. Additionally, the k-nearest neighbors (kNN) model revealed organic leaching from both MPs and the membrane, while ATR-FTIR results indicated membrane deterioration when NaOCl and IL were used. NaOH and NaCl, though slightly less effective, offer a more sustainable approach by avoiding toxic by-products, organic alterations, and membrane damage, making them preferable for long-term use.