Treatment and valorization of spent caustic brine: A critical review with emphasis on membrane technologies.

Spent caustic brine (SCB) is a hazardous yet resource-rich industrial waste, primarily composed of sodium hydroxide, water, and contaminants such as sulfides, phenols, organic compounds, heavy metals, and valuable minerals. Originating from industries such as oil and gas, metal finishing, and food processing, SCB poses high pH (>11), high total dissolved solids (up to 58,000 ppm), heavy metal content, and elevated chemical oxygen demand (COD). In this work, treatment and valorization methods for SCB are categorized into three groups: traditional techniques without caustic or water recovery, conventional techniques with limited recovery, and membrane technologies offering effective caustic and water recovery (85 % and 90 %, respectively). This review emphasizes membrane technologies due to their potential for resource recovery and environmental sustainability. Traditional and conventional methods are also discussed to provide a comprehensive overview. Unlike approaches that focus solely on treatment, this work critically examines valorization strategies that align with circular economy principles, aiming to recover valuable resources rather than dispose of them. The novelty of this study lies in its shift from waste treatment to resource and water recovery, promoting sustainable management practices. Future research should focus on advancing membrane technologies and integrating valorization pathways to minimize environmental impact and maximize economic benefits.