Antiscalants in Reverse Osmosis Concentrates: Impacts, Removal Strategies, and Pathways to Zero Liquid Discharge

The escalating demand for freshwater necessitates the optimization of desalination processes, particularly through reverse osmosis (RO) systems, which produce reverse osmosis concentrates (ROCs) laden with antiscalants. These chemical agents are used to prevent membrane scaling in RO systems but can complicate the achievement of zero liquid discharge (ZLD). Remaining antiscalants impede sustainable practices for eliminating liquid waste and maximizing water recovery. They lead to increased costs of salt and mineral crystallizers and difficulties in separating salts and minerals from ROCs. This review explores the types of antiscalants, including phosphorus-based, synthetic polymer-based, and eco-friendly variants, along with their operational and environmental impacts. The mechanisms behind their functions, the influence of thermodynamic parameters, and their effects on scaling are also discussed. A techno-economic analysis assesses the necessity for antiscalant removal and the potential economic benefits of including removal strategies in ROC management. Additionally, the review evaluates a range of antiscalant removal technologies and their integration into current desalination systems, with a focus on adsorption, nanofiltration, electrocoagulation, and advanced oxidation processes such as ozonation, UV/Fenton, UV/chlorine, UV/persulfate, peroxymonosulfate, photolysis, and electrochemical oxidation. The challenges, efficiencies, and integration potential of these methods are examined in depth to guide future design and operational strategies. This comprehensive overview not only addresses the complexities of managing antiscalants in ZLD systems but also underscores the importance of innovative removal technologies for sustainable desalination, contributing to more effective ZLD systems and enhanced water recovery in desalination processes.