What is the defining characteristic of Zero Liquid Discharge (ZLD) systems used in desalination brine management?

The defining characteristic of Zero Liquid Discharge (ZLD) systems used in desalination brine management is the complete elimination of liquid wastewater discharge from the desalination plant. Unlike conventional desalination processes that produce a concentrated brine stream that is typically discharged into the environment, ZLD systems treat the brine to recover water and solid salts, leaving no liquid effluent. This is achieved through a combination of technologies, including evaporation, crystallization, and solids handling. The brine is first concentrated using evaporators, such as mechanical vapor compression (MVC) or thermal vapor compression (TVC) evaporators, to reduce the volume of liquid. The concentrated brine is then fed to crystallizers, where the remaining water is evaporated, and the dissolved salts precipitate out as solid crystals. These solid salts are then collected and can be disposed of in a landfill or, in some cases, sold as industrial products. The water recovered from the evaporation and crystallization processes is recycled back into the desalination plant, increasing the overall water recovery rate. ZLD systems are more complex and energy-intensive than conventional desalination processes, but they offer a significant environmental benefit by eliminating the negative impacts associated with brine disposal. They are particularly suitable for inland desalination plants where discharge options are limited and for coastal plants in environmentally sensitive areas.