Zero-liquid discharge (ZLD) is a water treatment process in which all wastewater is purified and recycled; therefore, leaving zero discharge at the end of the treatment cycle. Zero liquid discharge is an advanced wastewater treatment method that includes ultrafiltration, reverse osmosis, evaporation&crystallization.
Zero liquid discharge can be defined broadly as a process for maximum recovery of water from a waste water source that would otherwise be discharged. This water is beneficially reused and the salts, and other solids contained in the waste water are produced and generally disposed in a landfill.
Zero liquid discharge can be achieved in various ways. There is no “one size fits all” solution, as the optimal system design is site specific. The waste water composition, various streams to be treated, site specific operating costs, foot print availability and other factors are determining factors for an optimal design.
The system objectives for a zero liquid discharge system are to eliminate a liquid waste water discharge, generate solids for landfill disposal or reuse, and to recycle a high-quality water that can be beneficially reused. The design objectives are to minimize the capital investment and system operating cost, while not significantly impacting the manpower required for operation. Further, the system must be designed with operational flexibility to meet the facility needs and be safe and reliable.
Waste Water Chemistry
Careful consideration of waste water chemistry is needed for the successful design and operation of a zero liquid discharge system. A sound water chemistry design basis is key to successful zero liquid discharge design.
In a zero liquid discharge system, the waste water being processed is concentrated to solubility limits of the dissolved salts. When the solubility limits are exceeded, salts crystallize and can then be harvested using an appropriate means.
Falling Film Evaporators
Forced Circulation Evaporators
Agitated Thin Film Dryers (ATFD)
Mechanical Vapour Recompression (MVRe)
Condensate Polishing System
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