Zero Liquid Discharge
Also called: ZLD · Topic: Geographical Issues: Pollution, Urban Waste, Slums and Land Degradation · NCERT: Beyond NCERT
Meaning
Zero Liquid Discharge (ZLD) is a system in which a factory cleans all of its wastewater and uses it again, so no liquid waste leaves the unit. The water is first treated. Then it is pushed through membrane filters, which are very fine sheets that let clean water pass and hold back salts and chemicals. The clean water goes back to the factory. The salty leftover, called reject or sludge, still has to be stored or disposed of on land. ZLD protects rivers and groundwater, but it uses a lot of electricity. About half its cost goes on energy, so small units find it hard to afford.
Example
In Tiruppur, Tamil Nadu, textile dyeing units released untreated waste into the Noyyal river. Farmers downstream suffered and went to court. In 2011 the Madras High Court ordered the units to pay the farmers compensation or install ZLD, and to close if they did neither. Many small units then shared common effluent treatment plants (CETPs), where one plant treats the wastewater of many units.
Don't confuse with
- Effluent treatment plant (ETP): an ETP cleans wastewater before it is released, but the treated water still goes out into a river or drain. Under ZLD, nothing is released, and all the water is used again.