ZLD systems provide numerous economic and environmental advantages for plant managers-water is recycled and reused, saving on the cost and treatment of raw water. Since all water is reclaimed, no effluent is discharged from the plant, avoiding the cost of environmental impact.
ZLD System Advantages
The ZLD System removes dissolved solids from the wastewater and returns distilled water to the process (source). Reverse osmosis (membrane filtration) may be used to concentrate a portion of the waste stream and return the clean permeate to the process. In this case, a much smaller volume (the reject) will require evaporation, thus enhancing performance and reducing power consumption. In many cases, falling film evaporation is used to further concentrate the brine prior to crystallization.
Falling film evaporation is an energy efficient method of evaporation, typically to concentrate the water up to the initial crystallization point. The resultant brine then enters a forced-circulation crystallizer where the water concentrates beyond the solubility of the contaminants and crystals are formed. The crystal-laden brine is dewatered in a filter press or centrifuge and the filtrate or centrate (also called 'mother liquor') is returned to the crystallizer. The collected condensate from the membranes, falling film evaporator and forced-circulation crystallizer is returned to the process eliminating the discharge of liquids. If any organics are present, condensate polishing may be required for final cleanup prior to reuse.