Seeking realistic membrane ageing at bench-scale

Fouling and cleaning of water treatment ultrafiltration membranes are well understood, but long-term changes (i.e. ageing) have not been fully explored. Changes in physical and chemical characteristics, and changes in membrane performance, have been attributed to ageing; however, the tools to probe these effects and their causality are limited. Most membrane ageing research focuses on bench-scale ageing of membranes, with scant attention to full-scale ageing or how bench-scale ageing can be useful in understanding full-scale ageing. The present research links membrane ageing changes observed at bench-scale with changes observed in previous full-scale studies. Two bench-scale ageing techniques were used to probe changes in performance and characteristics: soaking membranes in NaOCl as the cleaning agent, and cycling them with foulant and the cleaning agent. Changes in membrane chemistry were similar for both bench-scale and full-scale ageing, but performance differed. Membrane process complexity increases from bench-scale soaking, to bench-scale cycled operation, to full-scale operation. For some properties, the progression due to ageing differs depending on process complexity. By comparing the two bench-scale techniques with the full-scale ageing findings, it was established that irreversible foulants are critical components of full-scale ageing, and the impact of these foulants can be approximated to some extent by cycling membranes at bench-scale.