The Central Pollution Control Board's Zero Liquid Discharge notification has been on the books since 2016. But in 2025, enforcement is a different matter. The National Green Tribunal has issued closure orders to over 400 textile units in Gujarat and Tamil Nadu. PCBs are conducting surprise inspections. The days of ignoring ZLD compliance are over.
What is Zero Liquid Discharge?
Zero Liquid Discharge is not a single technology — it is a treatment outcome. A ZLD plant eliminates all liquid effluent discharge from an industrial site by treating wastewater to recover usable water and converting residual waste to a dry solid (typically salt). The plant boundary has no liquid outlet.
In practice, a ZLD train for a textile unit looks like this: raw effluent → ETP (biological + chemical) → RO concentration → Multiple Effect Evaporator (MEE) → Agitated Thin Film Dryer (ATFD) → dry salt. The recovered RO permeate (70–80% of the feed) returns to your process.
Which industries are affected by the ZLD mandate?
- Textile processing units in notified clusters (Tirupur, Surat, Panipat, Ludhiana)
- Pharmaceutical manufacturers classified as "Red" category
- Tanneries and leather processing units
- Dye and dye-intermediate manufacturers
- Caustic soda, soda ash, and chlor-alkali plants
- Sugar mills with attached distilleries
- Large hotels (>100 rooms) in some states per SPCB consent conditions
Penalties and enforcement actions
The Environment Protection Act (1986) empowers the CPCB and State PCBs to issue closure directions, environmental compensation orders, and FIRs under Section 15 of the Act (which carries imprisonment up to 7 years). The NGT has additionally imposed environmental penalties of ₹5 lakh to ₹2 crore per non-compliant unit in recent orders.
Technical requirements for a compliant ZLD plant
| Stage | Technology | Key Output Parameter |
|---|---|---|
| Pre-treatment | Primary ETP | TSS <50 mg/L, COD <500 mg/L (RO feed) |
| Secondary treatment | Biological (MBBR/SBR) | BOD <30 mg/L |
| RO concentration | High-rejection RO | Permeate TDS <100 mg/L; reject TDS 15,000–30,000 mg/L |
| Thermal evaporation | MEE (3-effect) | Condensate TDS <50 mg/L; concentrate 25–30% solids |
| Final drying | ATFD | Dry salt >98% purity |
What does ZLD cost?
Capital cost for a 500 KLD ZLD plant (ETP + RO + MEE + ATFD) typically ranges from ₹3.5 Cr to ₹5.5 Cr depending on inlet water quality, technology selection, and site constraints. Operating costs are ₹80–120 per KL treated, of which power is the largest component (MEE is thermally intensive).
Against this, a 500 KLD plant recovering 450 KLD of usable water saves ₹18–36 lakh/year in freshwater purchase costs (at ₹40–80/KL municipal tariff). With salt resale at ₹3–5/kg, payback periods of 4–6 years are common for self-financed plants. BOOT models eliminate the CAPEX consideration entirely.
How long does it take to commission a ZLD plant?
For a 500 KLD system: detailed engineering 6 weeks, procurement 8 weeks (overlapping), civil construction 10–12 weeks (overlapping), erection and commissioning 4–6 weeks. Total: 22–28 weeks from order placement to operation. PCB consent application should run in parallel — allow 8–12 weeks for consent processing.
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