ZLD eliminates liquid effluent entirely — all water is recovered as reuse-quality permeate and all dissolved solids are recovered as dry solids. Increasingly mandatory for high-salinity industrial dischargers in India, the Middle East, and Europe.
India's Central Pollution Control Board (CPCB) mandates ZLD for textile, dye, and sugar industries in 17 categorised industrial clusters. UAE and Saudi Arabia are extending ZLD obligations to petrochemical and refinery effluents. Compliance timelines are enforced through plant closure orders.
ZLD recovers 90–98% of feed water as high-purity permeate, returning it to the process. In water-stressed regions, ZLD is both an environmental obligation and an economic imperative: the alternative is purchasing treated water at escalating cost. See our water reuse systems.
The IED recast (2022) and associated BAT Conclusions are progressively requiring zero or near-zero effluent discharge for energy, chemical, and mining sectors. Facilities undergoing permit renewal should assess ZLD feasibility as part of the BAT assessment process.
For streams containing recoverable salts (NaCl, Na&sub2;SO&sub4;, NaHCO&sub3;, KCl), ZLD crystallisation can produce saleable by-products that offset operating overheads. A textile ZLD plant producing industrial-grade NaCl from brine can recover – depending on volume and purity.
ZLD is not a single technology but a train of complementary processes. System design is driven by feed TDS, volume, and target solid composition.
Suspended solids, oils, and organic loads are removed before membrane and thermal stages to prevent fouling and scaling. Typical processes: coagulation-flocculation, DAF, multimedia filtration, and self-cleaning filters. COD must typically be <100 mg/L for membrane feed.
Two-pass or high-recovery RO concentrates feed TDS by 3–7× while producing high-purity permeate for reuse. Antiscalant dosing and pH adjustment prevent carbonate and sulphate scaling. See our RO skid systems. RO concentrate typically contains 20,000–80,000 mg/L TDS at this stage.
MVR evaporation further concentrates RO reject to near-saturation (150,000–250,000 mg/L TDS). Steam generated by evaporation is mechanically recompressed and reused, making MVR substantially more energy-efficient than multi-effect evaporation at this scale. Condensate (distillate) is reuse-quality water. See our ZLD evaporation systems.
Forced-circulation or draft-tube-baffle (DTB) crystallisers operate at or near saturation to precipitate dissolved salts as recoverable crystals. Crystal slurry is dewatered in a centrifuge or filter press. Vapour condensate returns to the water recovery loop. See our ZLD crystalliser systems.
Dewatered salt cake is bagged for disposal or sale. Crystal purity determines value — a dedicated NaCl crystalliser followed by a Na&sub2;SO&sub4; crystalliser can produce two separate saleable products from a mixed brine. Residual mother liquor is returned to the crystalliser loop.
| Industry | Typical Feed TDS | Primary Driver | Key Challenge |
|---|---|---|---|
| Textile & Dyeing | 5,000–30,000 mg/L | CPCB mandate (India), colour discharge prohibition | High colour, reactive dyes resist conventional treatment |
| Petrochemical & Refinery | 10,000–50,000 mg/L | Produced water reinjection limits; arid locations | Hydrocarbons and H&sub2;S fouling of membrane stages |
| Power Generation (FGD blowdown) | 15,000–60,000 mg/L | US EPA ELG rule; EU IED BAT Conclusions | High sulphate, chloride, selenium, mercury |
| Pharmaceutical API | 2,000–15,000 mg/L | API containment; zero environmental release mandate | Trace pharmaceutical compounds in brine |
| Mining (acid mine drainage) | 5,000–40,000 mg/L | Water reuse in arid regions; discharge prohibition | Gypsum scaling; mixed sulphate/heavy metal brine |
| Chemical Manufacturing | Highly variable | Permit renewal; waste minimisation | Complex mixed salt streams; corrosive species |
Mechanical vapour recompression and multi-effect evaporation for brine concentration.
View EvaporationForced-circulation and DTB crystallisers for salt recovery and dry solid production.
View CrystallisationIndustry-specific ZLD case examples: textile, power, petrochemical, pharmaceutical.
View ApplicationsRO systems designed for 80–90% recovery as the primary concentration stage in ZLD trains.
View RO SystemsOur engineers are available to review your site conditions and recommend the most appropriate treatment solution.
Mechanical vapour recompression, thermal evaporators, and forced-circulation crystallisers for brine concentration.
View guide →Forced-circulation, draft-tube-baffle, and oslo crystallisers for salt harvest from concentrated brines.
View guide →ZLD case references across power, mining, textile, and pharma — feasibility, drivers, and technology selection.
View applications →Our expertise spans multiple industries with sector-specific water treatment solutions.