Zero liquid discharge
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Zero liquid discharge is a process that is beneficial to industrial and municipal organizations as well as the environment because it saves money and no effluent, or discharge, is left over. ZLD systems employ the most advanced wastewater treatment technologies to purify and recycle virtually all of the wastewater produced. Also Zero liquid discharge technologies help plants meet discharge and water reuse requirements, enabling businesses to:
- Meet stringent cooling tower blowdown and flue gas desulfurization (FGD) discharge regulations.
- Treat and recover valuable products from waste streams.
- Better manage produced water.
A Zero liquid discharge facility (ZLD), is an industrial plant without discharge of wastewaters. Target ZLD is normally reached by
- Waste water strong recovery[clarification needed]
- Separation by evaporation or boiling of water part of waste water not reusable, in evaporators, crystallizers and condensate recovery. 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. The water vapor from evaporation is condensed and returned to the process.
The state of Tamil Nadu in India has made ZLD mandatory for all its industries.
Normally the evaporation-crystallizing section receives the reject from a reverse osmosis section  that concentrates dissolved solids. To prevent fouling during the reverse osmosis process, ultrafiltration is often used to eliminate suspended solids.
The TargetZero association promotes the use of ZLD technology.
- High pressure reverse osmosis for wastewater minimization and zero liquid discharge applications. Petra Johannsena, Ram Karlapudib, Georg Reinholdc Desalination 199 (2006) 84–85 Elsevier B.V. Archived July 14, 2007, at the Wayback Machine.
- Evaluation and Selection of Available Processes for a Zero-Liquid Discharge System for the Perris, California, Ground Water Basin Archived October 29, 2013, at the Wayback Machine.
- TargetZero association HomePage