Water is most essential but scarce resource in our country. Presently the quality & the availability of the fresh water resources is the most pressing of the many environmental challenges on the national horizon. The stress on water resources is from multiple sources and the impacts can take diverse forms. Geometric increase in population coupled with rapid urbanization, industrialization and agricultural development has resulted in high impact on quality and quantity of water in our country. The situation warrants immediate redressal through radically improved water resource and water quality management strategies. Zero liquid discharge ( ZLD ) is one of the main focus areas among all the new proposed standards to maintain the water quality & prevent water pollution.

What is Zero Liquid Discharge ( ZLD ) ?

Zero Liquid discharge ( ZLD ) refers to installation of facilities and system which will enable industrial effluent for absolute recycling of permeate and converting solute (dissolved organic and in-organic compounds/salts) into residue in the solid form by adopting method of concentration and thermal evaporation though solar or other technologies.

ZLD is recognized and certified based on two broad parameters:

1. Water consumption versus waste water re-used or recycled (permeate) &
2. Corresponding solids recovered (percent total dissolved / suspended solids in effluents).

How to achieve ZLD ?

ZLD can be achieved by adopting conventional primary, secondary and tertiary effluent treatment and polishing by filtration and using clean water back into process / or domestic use.

Basic Benefits of ZLD:

• ZLD implies no surface / ground water pollution from industries.
• Reduction in water consumption.
• Conservation of ground water, avoiding its rapid depletion.

Water Polluting Industries:

The water polluting industries discharge their effluent having high organic contents measured in-terms of bio-chemical oxygen demand (BOD), and other toxic constituents like metals, organic and in-organic compounds. The industries identified as water polluting industries by CPCB are: – Sugar, Distilleries, Pulp and Paper, Tanneries, Chemicals, Dyeing and Textiles, Refineries, Food, Dairy and Beverages, Electroplating and others.