Zero Liquid Discharge (ZLD)

Zero Liquid Discharge (ZLD) is an advanced wastewater treatment process that aims to eliminate liquid effluents from industrial processes. This is achieved by recovering and reusing water, while converting the remaining contaminants into solid waste.

Role of MEE, MVR, and ATFD

  • Multi-Effect Evaporator (MEE): This technology utilizes multiple stages to efficiently evaporate water from the wastewater. Heat from the vapor produced in one stage is used to heat the feed in the next stage, significantly reducing energy consumption.
  • Mechanical Vapor Recompressor (MVR): MVR is a highly energy-efficient process that compresses the vapor produced in the evaporation process to increase its temperature. This compressed vapor is then used to heat the incoming wastewater, further reducing energy requirements.
  • Agitated Thin Film Dryer (ATFD): This technology is used to dry the concentrated brine produced in the evaporation stages, converting it into a solid form.

ZLD Process Flow

A typical ZLD system using MEE, MVR, and ATFD involves the following steps:

  • Pre-treatment: Wastewater undergoes preliminary treatment to remove suspended solids and other contaminants.
  • Reverse Osmosis (RO): A significant portion of the water is recovered through RO, producing a concentrated brine.
  • Evaporation: The brine is fed into the MEE and MVR system to evaporate water, resulting in a highly concentrated solution.
  • Crystallization: The concentrated solution is further processed in a crystallizer to form solid salts.
  • Drying: The solid salts are dried using an ATFD to produce a dry, solid product.

Benefits of ZLD

  • Water conservation: Maximizes water reuse and reduces dependence on fresh water sources.  
  • Environmental protection: Prevents water pollution and minimizes the discharge of harmful substances.
  • Resource recovery: Enables recovery of valuable minerals and salts from wastewater.
  • Compliance: Helps industries meet stringent environmental regulations.

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