Extreme-pH, high-temperature regeneration of end-of-life RO membranes for semiconductor ultrapure water production: Performance recovery and full-scale field assessment

Abstract

High-temperature, extreme-pH cleaning can regenerate end-of-life reverse osmosis (RO) membranes for reuse in ultrapure water (UPW) systems. In lab-scale tests, a two-step protocol—60 °C NaOH followed by HCl—restored ≥95% of original water permeability while keeping salt rejection loss under 2.8%. Fouling analysis confirmed the presence of organic-dominant composite layers with embedded silica and metals, which were effectively removed by sequential chemical treatment. Twelve full-size elements underwent full-scale cleaning, of which eight met reuse criteria (≥95% flux recovery, <3% rejection loss). Field testing over 214 days demonstrated that regenerated modules maintained a lower absolute TMP rise (0.85 bar, 7.71%) than newly installed RO elements (0.93–1.02 bar), owing to prior compaction and structural stabilization. Salt rejection in regenerated elements improved from 98.8% to 98.9%, while new membranes showed slight declines, converging near 99.5%. These results confirm that properly regenerated and screened RO membranes can deliver performance equivalent to new elements in UPW systems. Adopting a selective reuse strategy based on membrane history and post-cleaning performance offers a practical path toward reduced waste, extended module life, and more circular membrane management in high-purity water applications.