Nutrient recovery in zero liquid discharge systems: A critical review of technologies and integration strategies

Zero liquid discharge (ZLD) systems are increasingly being implemented as sustainable water management solutions to address rising water scarcity, stringent environmental regulations, and global sustainability targets. Beyond water recovery, there is a growing need to recover nutrients, particularly nitrogen and phosphorus, from industrial and municipal wastewaters due to rising fertilizer costs and concerns over nutrient pollution and eutrophication. This review critically examines nutrient recovery within ZLD frameworks, including membrane-based concentration, thermally enhanced crystallization, biological processes, and hybrid systems. It synthesizes recent innovations and integration strategies to enable simultaneous water and nutrient recovery. Emphasis is placed on their mechanisms, recovery efficiencies, and integration potential. Regulatory drivers, including nutrient discharge limits and Sustainable Development Goals (notably SDGs 6 and 12), underscore the urgency of advancing nutrient recovery in ZLD systems. While economic and technical barriers persist, innovations in process integration and renewable energy utilization offer promising pathways forward. This review aims to inform future research and implementation of ZLD strategies that enable circular resource recovery and environmental protection.