Zero Liquid Discharge (ZLD)

Zero Liquid Discharge is an industrial effluent-management standard under which a factory or processing unit treats and recycles all of its wastewater internally, so that no liquid effluent is released into a river, drain or the wider environment. The treated water is recovered and reused within the industrial process, while the concentrated solid residue that remains after treatment is managed as solid waste, typically requiring separate, specialised disposal. ZLD is most commonly mandated for water-intensive, high-pollution-load industries such as textile dyeing and printing, tanneries, and certain chemical processing units, where effluent carries dyes, salts and heavy metals that conventional Effluent Treatment Plants (ETPs) do not fully remove. It is a more stringent standard than conventional treatment, since ordinary ETPs typically treat effluent to a permissible discharge concentration and then release the treated water into a water body, whereas ZLD eliminates the discharge pathway altogether. The standard is particularly consequential in arid or water-stressed river basins, where a low or seasonal natural flow gives a receiving river very little dilution capacity, so even treated effluent released at legally permissible concentrations can degrade water quality severely. Courts and pollution control boards have increasingly imposed ZLD obligations on industrial clusters located on such rivers as a condition of continued operation, reflecting a judgment that conventional treat-and-release regulation is inadequate for basins that cannot assimilate any additional load.

• 1 ZLD: no liquid effluent leaves the industrial plant boundary; water is recovered/reused internally, solids are separated for disposal.
• 2 More stringent than conventional Effluent Treatment Plant (ETP) standards, which typically treat-and-release into a water body.
• 3 Most commonly mandated for water-intensive, high-pollution-load industries: textile dyeing/printing, tanneries, chemical processing.
• 4 Particularly important in arid or seasonal river basins with minimal dilution capacity, where even treated discharge can severely degrade water quality.
• 5 Increasingly imposed by courts and pollution control boards as a condition of continued industrial operation in such basins.
• 6 The Supreme Court's 2026 order on the Jojari, Luni and Bandi rivers in Rajasthan required a ZLD obligation as part of the state's proposed 20-point revival plan for the textile-dyeing belt around Pali, Jodhpur and Balotra.

The Supreme Court's 2026 direction on Rajasthan's Jojari river required industry above 100 KLD capacity to move toward Zero Liquid Discharge, reflecting the judgment that a seasonal, low-flow river in an arid basin cannot safely absorb even treated effluent.