Zero Liquid Discharge (ZLD) is a treatment process that its goal is to remove all the liquid waste from a system.

Zero Liquid Discharge Plant is a treatment process that its goal is to remove all the liquid waste from a system. The focus of ZLD is to reduce economically wastewater and produce clean water that is suitable for reuse, thus saving money and being beneficial to the environment. ZLD systems employ the most advanced wastewater treatment technologies to purify and recycle virtually all of the wastewater produced.

Zero Liquid Discharge technology includes pre-treatment and evaporation of the industrial effluent until the dissolved solids precipitate as crystals. These crystals are removed and dewatered with a filter press or a centrifuge. The water vapor from evaporation is condensed and returned to the process.Pre-concentrating the brine is usually achieved with membrane brine concentrators or electrodialysis (ED). These technologies concentrate the stream to a high salinity and are able to recover up to 60–80% of the water.

The next step with thermal processes or evaporation, evaporates all the leftover water, collect it, and drives it for reuse. The waste that is left behind then goes to a crystallizer which boils all the water until all the impurities crystallize and are filtered out as a solid.