ETP for Tannery & Leather Industry
Turnkey ETP systems for tanneries handling chrome-tan, vegetable-tan, and combination-tan processes — chrome recovery units, sulphide destruction, high-TDS biological treatment, and ZLD for CPCB red category compliance in leather processing clusters
Industry Overview
ETP for Tannery & Leather Industry
India's tannery industry — concentrated in Tamil Nadu (Vellore, Chennai), West Bengal (Kolkata), Uttar Pradesh (Kanpur, Agra), Punjab (Jalandhar), Maharashtra (Dharavi), and Rajasthan (Jaipur) — is classified as a CPCB Red Category industry. Tannery wastewater is among the most complex industrial effluents: extremely high TDS (30,000–80,000 mg/L), BOD 1,500–5,000 mg/L, COD 3,000–15,000 mg/L, sulphide 100–500 mg/L, and hexavalent chromium (in chrome-tanning wastewater) 50–500 mg/L. National Green Tribunal orders and CPCB mandates require chrome recovery and ZLD or near-ZLD for large tanneries.
Tannery wastewater treatment requires a multi-stream approach. Chromium-containing liquor from chrome tanning must be separated at source and treated by chrome recovery units (alkali precipitation, chrome reuse). Sulphide-containing unhairing liquours require oxidative destruction (H₂O₂ or manganese dioxide catalytic oxidation) before entering the biological stage. Combined effluent after primary treatment has BOD 600–1,500 mg/L and TDS 15,000–30,000 mg/L, requiring salt-tolerant biological treatment — MBBR biofilm systems generally outperform activated sludge at high TDS.
Spans Envirotech designs standalone tannery ETPs and contributes technology to CETP schemes serving leather clusters. Our experience includes chrome recovery units, sulphide destruction systems, MBBR biological treatment at high TDS, and integration with RO and evaporation systems for ZLD. For CETP applications see our dedicated CETP for Tannery Clusters page. Standalone tannery ETPs typically serve individual units of 50–500 KLD capacity.
Industry Challenges
Key Environmental Challenges
Chrome Recovery and Hexavalent Chrome Risk
Chrome tanning liquor contains Cr³⁺ at 1,500–5,000 mg/L. CPCB prohibits Cr³⁺ discharge above 2 mg/L and Cr⁶⁺ above 0.1 mg/L. Chrome must be recovered and reused (alkali precipitation at pH 8.0–8.5 recovers 90–95% of chrome as basic chromium sulphate cake for reuse). Without chrome recovery, total chromium in treated effluent routinely exceeds limits, leading to SPCB closure orders.
Sulphide Destruction from Unhairing Liming
Sodium sulphide used in unhairing (lime-sulphide process) generates wastewater with sulphide 200–800 mg/L and pH 11–13. At low pH, this produces toxic H₂S gas. Sulphide must be oxidised (catalytic oxidation with MnO₂ or H₂O₂ dosing) before biological treatment. CPCB discharge limit for sulphide is 2 mg/L.
Extreme TDS Inhibiting Biological Treatment
Combined tannery wastewater TDS of 15,000–40,000 mg/L inhibits conventional activated sludge microorganisms. MBBR biofilm bacteria adapted to high salt concentrations maintain biological activity at TDS up to 20,000 mg/L with gradual acclimatisation. Above 30,000 mg/L, dilution or RO treatment before biological stage may be required.
High Ammonia from Soaking and Liming
Hide soaking and protein breakdown generates ammonia-N 100–300 mg/L. Combined with high TDS and sulphide inhibition, nitrification is challenging. Two-stage MBBR (BOD removal + dedicated nitrification) with longer HRT achieves ammonia removal even in high-TDS conditions.
ZLD Requirement for Red Category Compliance
NGT orders and CPCB mandates in several states (Tamil Nadu, West Bengal, Rajasthan) require tanneries to achieve ZLD or connect to a compliant CETP. Standalone tannery ZLD involves RO (to concentrate TDS and recover water) followed by MEE (Multi-Effect Evaporation) to crystallise the salt concentrate. ZLD capital costs are high (₹3–8 crore for a 100 KLD tannery) but mandatory for continued operation.
Our Solutions
Tailored Wastewater Treatment Solutions
Chrome Recovery Unit
Segregated chrome tanning liquors treated by alkali precipitation (NaOH or MgO at pH 8.0–8.5) recover 90–95% of chromium as basic chromium sulphate for reuse in subsequent tanning batches. Chrome recovery pays back in 18–30 months from chromium salt savings (chrome salts cost ₹80–120/kg). Recovered chrome meets leather sector quality standards for reuse.
Sulphide Destruction System
Hydrogen peroxide (H₂O₂) or manganese dioxide catalytic oxidation systems destroy sulphide from liming liquors. Target: sulphide <2 mg/L before biological stage. Sulphide oxidation also reduces BOD load entering biological treatment, improving overall performance.
High-TDS MBBR Biological Treatment
MBBR systems with 40–55% carrier filling ratio, extended HRT of 16–24 hours, and high DO (3–4 mg/L) achieve BOD removal from tannery effluent even at TDS 15,000–20,000 mg/L after acclimatisation. Two-stage MBBR design: stage 1 for BOD removal, stage 2 for nitrification.
RO and Evaporation for ZLD
After biological treatment and polishing, RO concentrates the permeate to 95–98% water recovery. The high-TDS concentrate (50,000–100,000 mg/L) is fed to a Multiple Effect Evaporator (MEE) to crystallise mixed salts. The recovered distillate is recycled to the process. Mixed salt disposal is managed under Hazardous Waste Rules.
Compliance Documentation and CPCB Reporting
SCADA monitoring with online TDS, TSS, pH, chromium, and sulphide sensors. Automated monthly reports for SPCB Form V submissions. Chrome recovery records as required under Hazardous Waste Rules. OCEMS installation for Red Category compliance.
Technologies
Proven Technologies for Your Industry
Benefits
Why Choose Spans for Your Industry
- Chrome recovery reduces chromium salt costs by ₹10–25 Lakh/year for medium tanneries
- CPCB Red Category compliance — Cr <2 mg/L, sulphide <2 mg/L, BOD <30 mg/L
- ZLD option available for NGT-mandated zero discharge tanneries
- MBBR tolerates high TDS conditions where activated sludge fails
- OCEMS-ready system meets state PCB monitoring requirements
- Integration with CETP where individual ZLD is not viable
Success Stories
Case Studies
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