Zero Liquid Discharge: An Overview

Abstract

A well-designed Zero Liquid Discharge (ZLD) system aims to produce a clean stream that may be used elsewhere in the plant's processes while minimising the amount of liquid waste that needs to be treated. Concentrating (evaporating) wastewater before disposing of it as a liquid brine or further crystalizing the brine into a solid is a typical ZLD strategy. While the brine is continuously concentrated to achieve a greater solids concentration, the evaporated water is recovered and recycled. It is intended that the effluents be treated to adhere to the legal restrictions. The Pollution Control Board has established acceptable thresholds for COD and total suspended solids, and the pH must be neutral. The removed waste is categorized as organic and inorganic waste and is treated accordingly. The purified water can be utilized again for tasks like gardening, boiler feed, etc. Other byproducts produced during treatment, like hydrocarbons and lead, are put to use or sold in accordance with market demands. The practice of treating wastewater is known as "Zero Liquid Discharge" since it prevents the industry from wasting any water at all while still enabling compliance with pollution control board standards. Engineers' responsibilities in Zero Liquid Discharge plants include maximizing operating costs, improving steam economy, and enhancing solvent recovery.