ZeroLiquidDischarge

Zero liquid discharge (ZLD) is a water treatment strategy designed to eliminate liquid effluent from a facility by reclaiming and reusing as much process water as possible. The objective is to minimize freshwater intake and to produce solid waste in the form of crystalline salts rather than releasing contaminated liquid to the environment.

ZLD systems typically integrate pretreatment and high-recovery filtration with brine concentration and crystallization. Pretreatment removes particulates and organics; membranes such as reverse osmosis or nanofiltration recover clean water from highly concentrated streams. The remaining brine is processed in evaporators or crystallizers, which further concentrate water and produce solid salts.

Applications include power plants, chemical production, metal finishing, mining, textiles, pharmaceuticals, and food and beverage processing. ZLD is favored in regions with water scarcity, strict discharge limits, or long-term water security goals.

Benefits include reduced freshwater withdrawals, compliance with environmental regulations, and reduced effluent toxicity. ZLD can lower long-term operating costs in high-cost water areas, but it typically requires substantial capital investment and high energy consumption.

Challenges involve high capital and operating costs, complex operations, fouling and scaling of membranes, handling and disposal of recovered solids, and the need for skilled management. In some cases, near-ZLD or hybrid approaches are used to balance cost and water recovery.