ZLD for Tannery & Leather Industry
Zero liquid discharge for tanneries — chrome recovery, sulphide destruction, biological treatment, and RO + MEE in compliance with CPCB and NGT directions
Industry Overview
ZLD for Tannery & Leather Industry
Tannery and leather processing effluent is among the most complex and hazardous of all industrial wastewaters — containing Cr³⁺ from chrome tanning, sulphide from liming and unhairing, high TDS from salt curing, high BOD and COD from hide proteins, and suspended solids including hair and flesh pieces. CPCB classifies tanneries as Red Category industries, and the National Green Tribunal has issued specific directions requiring Zero Liquid Discharge for tanneries in major leather clusters including Ranipet and Vellore in Tamil Nadu, Kanpur and Agra in Uttar Pradesh, Kolkata in West Bengal, and Jalandhar in Punjab. Achieving ZLD requires a carefully sequenced multi-stream treatment approach in which chrome recovery and sulphide destruction must be completed before biological treatment can begin. For general tannery effluent treatment options, see our Tannery Wastewater Treatment page; for ZLD system details, see our Zero Liquid Discharge ZLD page.
The treatment train begins with stream segregation: chrome-bearing liquor from the tanning drum is collected separately for alkali precipitation of Cr(OH)₃, chrome cake recovery, and recycling of recovered chrome back to the tanning drum — simultaneously removing chrome toxicity from the main effluent stream and recovering the raw material. Beam house wastewater containing sulphide undergoes aeration or catalytic oxidation at elevated pH to convert sulphide to sulphate before blending with the main stream. The combined, chrome-recovered, sulphide-destroyed stream then enters biological treatment — typically MBBR — followed by secondary clarification, UF, and two-pass RO. Given the high TDS of tannery effluent (8,000–25,000 mg/L after biological treatment), achieving 75–85% water recovery requires careful RO system engineering with appropriate anti-scalant dosing and inter-stage pressure management. See our MBBR for Tannery Wastewater page for biological treatment details, and our DAF Dissolved Air Flotation page for primary separation.
Spans Envirotech has direct experience with Common Effluent Treatment Plant (CETP) design and operation for leather clusters, including the tannery CETP at Jalandhar, and brings this practical understanding of the chrome recovery, sulphide chemistry, and high-TDS RO challenges specific to the tanning sector. Our ZLD designs for tanneries integrate chrome recovery systems, sulphide management, biological treatment, and membrane concentration with the specific operational constraints of cluster and standalone tannery environments.
Industry Challenges
Key Environmental Challenges
Chrome Toxicity to Biological Treatment
Cr³⁺ from chrome tanning liquor at concentrations above 5 mg/L is toxic to aerobic bacteria; chrome recovery by alkali precipitation is a non-negotiable pre-treatment step before any biological treatment can function.
Sulphide Destruction from Liming Operations
Spent liming liquor contains sulphide at 200–500 mg/L; at pH <9 this generates toxic H₂S gas; sulphide must be destroyed by aeration or catalytic oxidation at controlled alkaline pH before blending with the main effluent stream.
Very High TDS Limiting RO Recovery
Tannery effluent TDS after biological treatment reaches 8,000–25,000 mg/L from salt-curing chemicals and tanning salts; this high osmotic pressure limits single-pass RO recovery to 55–70% and requires two-pass RO + MEE for ZLD closure.
Hazardous Sludge and Salt Cake Management
Chrome sludge (Cr(OH)₃), primary biological sludge, and MEE salt cake may be classified as hazardous waste under the Hazardous Waste Management Rules — requiring TSDF (Treatment, Storage and Disposal Facility) disposal, adding to ZLD operating cost.
Compliance with Multiple Regulatory Authorities
Tanneries must comply with CPCB directions, State PCB conditions, NGT orders, and — for exporters — with buyer and brand sustainability requirements; this multi-authority compliance landscape requires robust monitoring, record-keeping, and OCEMS installation.
Our Solutions
Tailored Wastewater Treatment Solutions
Chrome Recovery System
Dedicated chrome-bearing liquor collection, alkali precipitation with NaOH at pH 8–9 to precipitate Cr(OH)₃, chrome cake filtration and acidification with H₂SO₄ for chrome liquor reconstitution and recycling to the tanning drum — reducing both chrome discharge and raw material cost.
Sulphide Destruction Unit
Separate beam house effluent collection, aeration at pH >9.5 to convert S²⁻ to sulphate by oxidation, with pH monitoring and control to prevent H₂S emission; outlet sulphide <2 mg/L before blending with the main effluent stream.
MBBR Biological Treatment
MBBR with sufficient HRT and media volume to handle the high BOD/COD load after chrome recovery and sulphide destruction, with appropriate nutrient dosing (urea/DAP) given the nitrogen-deficient character of hide-protein organics.
Two-Pass RO Membrane System
High-pressure two-pass RO configured for tannery's high TDS inlet, with anti-scalant dosing engineered for the specific ion mix (calcium, sulphate, sodium chloride); permeate reused as process water in the tannery; brine routed to MEE.
MEE and Crystalliser for Brine Concentration
Multiple Effect Evaporator concentrates RO brine for final salt cake crystallisation; MEE condensate is polished and recirculated; salt cake — predominantly NaCl — is characterised for TSDF or industrial salt reuse depending on purity.
Technologies
Proven Technologies for Your Industry
Benefits
Why Choose Spans for Your Industry
- NGT and CPCB ZLD Compliance — achieves Zero Liquid Discharge in compliance with National Green Tribunal orders and CPCB directions targeting major Indian leather clusters
- Chrome Recovery Reduces Chemical Cost — chrome recovery and recycling reduces Cr₂(SO₄)₃ consumption by 30–40%, converting a compliance obligation into a process efficiency improvement
- Sulphide Risk Elimination — dedicated sulphide destruction eliminates H₂S toxicity risk in both the wastewater and the plant environment, protecting workers and the biological treatment system
- 75–85% Water Recovery — two-pass RO + MEE achieves high overall water recovery despite the high TDS of tannery effluent, reducing freshwater intake and groundwater extraction
- Export Market Compliance — ZLD compliance and OCEMS-monitored discharge records support sustainability requirements from international leather buyers and brand audits
- CETP Integration Capability — Spans Envirotech has direct CETP design experience for leather clusters, enabling ZLD design for both standalone tanneries and common effluent treatment facilities
Success Stories
Case Studies
Ready to Transform Your ZLD for Tannery & Leather Industry Operations?
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