Zero liquid discharge
Zero Liquid Discharge (ZLD) is a treatment process designed to remove all the liquid waste from a system. The focus of ZLD is to reduce wastewater economically and produce clean water that is suitable for reuse (e.g. irrigation), thereby saving money and being beneficial to the environment. ZLD systems employ advanced wastewater/desalination treatment technologies to purify and recycle virtually all of the wastewater produced. Also ZLD technologies help plants meet discharge and water reuse requirements, enabling businesses to: The conventional way to reach ZLD is with thermal technologies such as evaporators (multi stage flash (MSF), multi  effect distillation (MED) and mechanical vapor compression (MCV)) and crystallizers and recover their condensate. Thus, ZLD plants produce solid waste. ZLD discharge system overview. ZLD 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. In the last decades though, there has been an effort from the water treatment industry to revolutionize the high water recovery and ZLD technologies. This has led to processes like electrodialysis (ED/EDR ), forward osmosis (FO) and membrane distillation (MD). A quick overview and comparison can be seen by the following table, Configuration. Despite the variable sources of a wastewater stream, a ZLD system is generally comprised by two steps