The GATE Grind

GATE 2025 ES – Question 19

Water and Wastewater Treatment and Management · Industrial Effluents and Reuse · 1 mark · Multiple choice

In zero liquid discharge, a multiple-effect evaporator is commonly used for

  1. Oxidation of organic pollutants
  2. Precipitation of heavy metals
  3. Concentrating RO reject salts
  4. Selective ion exchange

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Correct answer: (C) Concentrating RO reject salts

Explanation

A multiple-effect evaporator reuses vapor heat across successive effects to evaporate water efficiently. In ZLD it concentrates the saline RO reject toward crystallization while recovering water. It does not primarily perform oxidation, metal precipitation or selective ion exchange. Thus **C**.

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