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<p>The global expansion of reverse osmosis (RO) desalination plants over the past decade has resulted in a significant accumulation of discarded membranes, which are non-biodegradable and environmentally problematic. Repurposing spent RO elements into nanofiltration (NF) or ultrafiltration (UF) membranes offers a sustainable management strategy. In this study, a used RO membrane from a small desalination unit in Hurghada was subjected to cleaning and chemical modification. Surface cleaning with hydrochloric acid (pH 2) and sodium hydroxide (pH 12) effectively removed inorganic deposits, with acid showing higher efficiency. Conversion to NF was achieved by partial degradation of the polyamide layer using oxidizing agents, including sodium hypochlorite (NaOCl), hydrogen peroxide (H₂O₂), and potassium permanganate (KMnO₄), applied at concentrations of 1000–7000 ppm·h. The optimum performance was obtained with 3000 ppm·h NaOCl treatment, yielding salt rejection of 92–95.4% and water fluxes of 20.1–26&#xa0;L/m²·h for NaCl, MgSO₄, Na₂SO₄, and MgCl₂. Compared with the untreated membrane, flux increased nearly threefold while rejection remained comparable. Stability over 24&#xa0;h confirmed NaOCl’s suitability for controlled degradation. The combined process of cleaning followed by polyamide modification provides a reliable method for recycling spent RO membranes, enhancing flux performance, and reducing their environmental footprint.</p>

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Reprocessing spent-life reverse osmosis membranes into nanofiltration membranes via controlled polyamide layer degradation

  • 期刊论文

  • 发表日期：

    2025年12月15日

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  • Reham Bosela,
  • Rand Ghanoum,
  • Hosam A. Shawky,
  • Mohamed E. A. Ali

摘要

The global expansion of reverse osmosis (RO) desalination plants over the past decade has resulted in a significant accumulation of discarded membranes, which are non-biodegradable and environmentally problematic. Repurposing spent RO elements into nanofiltration (NF) or ultrafiltration (UF) membranes offers a sustainable management strategy. In this study, a used RO membrane from a small desalination unit in Hurghada was subjected to cleaning and chemical modification. Surface cleaning with hydrochloric acid (pH 2) and sodium hydroxide (pH 12) effectively removed inorganic deposits, with acid showing higher efficiency. Conversion to NF was achieved by partial degradation of the polyamide layer using oxidizing agents, including sodium hypochlorite (NaOCl), hydrogen peroxide (H₂O₂), and potassium permanganate (KMnO₄), applied at concentrations of 1000–7000 ppm·h. The optimum performance was obtained with 3000 ppm·h NaOCl treatment, yielding salt rejection of 92–95.4% and water fluxes of 20.1–26 L/m²·h for NaCl, MgSO₄, Na₂SO₄, and MgCl₂. Compared with the untreated membrane, flux increased nearly threefold while rejection remained comparable. Stability over 24 h confirmed NaOCl’s suitability for controlled degradation. The combined process of cleaning followed by polyamide modification provides a reliable method for recycling spent RO membranes, enhancing flux performance, and reducing their environmental footprint.