Environmental and economic concerns necessitate the recycle of end-of-life (EOL) reverse osmosis (RO) membranes. Controlled downcycling of EOL RO membrane to nanofiltration (NF)-like or ultrafiltration (UF)-like membrane through regulating sodium hypochlorite (NaClO) exposure doses has been developed in recent years. However, the impact of foulants on the chlorination-based membrane downcycling is often overlooked. An alkaline-NaClO treatment strategy was employed to downcycle Si-Al complex-fouled EOL RO membrane. Alkaline cleaning not only partially removed Si-Al complex foulants via dissolution, but also converted Al₂O₃·SiO₂ to Al-O-Si amorphous oxides. Subsequent NaClO treatment gradually deconstructed the Si-Al complex fouling layer by dissolving Al contained in Al-O-Si amorphous oxides and degraded the polyamide (PA) layer with extended exposure time, resulting in membrane with loose NF-like characteristic. Moreover, the conversion of Al-contained component with alkaline pre-treatment prevented Al³⁺-catalyzed degradation of PA layer and ensure controlled downcycling. For the downcycling to UF-like membrane, complete removal of PA layer with sufficient chlorine oxidation was essential while alkaline pre-treatment process was optional. Both downcycled loose NF-like and UF-like membranes exhibited satisfactory filtration and antifouling performance. Our study presents an effective and robust protocol for controllable downcycling of EOL RO membrane with alkaline pre-treatment based on their fouling characteristic.

出于环境和经济考虑，需要对报废 (EOL) 反渗透 (RO) 膜进行回收。近年来，通过调节次氯酸钠 (NaClO) 暴露剂量，将 EOL RO 膜控制降级为类纳滤 (NF) 或类超滤 (UF) 膜。然而，污染物对基于氯化的膜降级循环的影响常常被忽视。采用碱性-NaClO 处理策略来降低 Si-Al 复合物污染的 EOL RO 膜的循环。碱洗不仅通过溶解部分去除了Si-Al络合物污染物，而且将Al ₂ O ₃ ·SiO ₂转化为Al-O-Si非晶氧化物。随后的 NaClO 处理通过溶解 Al-O-Si 无定形氧化物中的 Al 来逐渐解构 Si-Al 复合污垢层，并随着暴露时间的延长而降解聚酰胺（PA）层，导致膜具有松散的类 NF 特性。此外，通过碱性预处理对含Al组分进行转化，防止了Al ³⁺催化的PA层降解，并确保了受控的降级循环。对于降级为类超滤膜，必须通过充分的氯氧化来完全去除 PA 层，而碱性预处理工艺是可选的。降级循环的松散类NF膜和类UF膜均表现出令人满意的过滤和防污性能。我们的研究提出了一种有效且稳健的方案，用于根据污垢特性对 EOL RO 膜进行碱性预处理的可控降级循环。