Tannery Wastewater Treatment — India
Multi-stage effluent treatment systems for tanneries and leather processing industries — chromium recovery and recycling, sulphide oxidation, biological treatment, and ZLD for Kanpur, Unnao, Ambur, Ranipet, Kolkata, and export leather clusters
Industry Overview
Tannery Wastewater Treatment — India
India's leather and tannery industry is one of the largest in the world — processing hides and skins from cattle, buffalo, sheep, and goat to produce finished leather for footwear, garments, accessories, and automotive upholstery. Major tannery clusters are located in Kanpur and Unnao (Uttar Pradesh), Ambur and Ranipet (Tamil Nadu), Kolkata (West Bengal), and Jalandhar (Punjab). The industry generates some of the most complex and environmentally hazardous industrial wastewater in India — requiring multi-stage treatment systems that go well beyond what standard ETPs for food or pharmaceutical clients require.
Tannery wastewater contains a cocktail of pollutants: Trivalent Chromium from chrome tanning (50–500 mg/L in concentrated chrome tan liquor; 20–100 mg/L in mixed effluent), Sulphides from beamhouse liming and dehairing operations (50–200 mg/L), high BOD from organic matter (hide proteins, fat, blood), TDS 20,000–80,000 mg/L from salt curing and tanning chemicals, and colour from vegetable tannins and synthetic dyes. Each of these requires specific treatment — and in most cases, the sequence of treatment is as critical as the treatment technology itself.
Spans Envirotech designs and supplies multi-stage tannery ETPs with integrated chrome recovery systems — recovering valuable Cr(OH)₃ for recycling back to the tanning process, which simultaneously reduces pollution load and operating costs. Our tannery ETP designs incorporate stream segregation at source (chrome streams, sulphide streams, vegetable tannin streams), targeted pre-treatment for each stream, combined biological treatment, and ZLD where mandated by state PCBs in Kanpur-Unnao and Ambur-Ranipet clusters.
Industry Challenges
Key Environmental Challenges
Total Chromium Removal to <2 mg/L
CPCB mandates Total Chromium <2 mg/L in treated effluent — requiring complete chromium removal from mixed tannery wastewater that may carry 20–100 mg/L Cr in combined streams. Chrome-bearing streams must be segregated at source and subjected to alkaline precipitation (pH 8.5–9.0) to precipitate Cr(OH)₃ before mixing with other streams. Residual chromium in biological treatment must be controlled below 5 mg/L to prevent inhibition of biological treatment microorganisms.
Sulphide Toxicity
Sulphide (S²⁻) at concentrations above 1–2 mg/L is toxic to aerobic biological treatment microorganisms and can completely crash an aeration basin. Beamhouse effluent carries 50–200 mg/L S²⁻ and must be segregated and pre-treated by sulphide oxidation (air sparging, H₂O₂ addition, or ozone) before mixing with the main biological treatment stream. Sulphide also produces H₂S gas — creating odour problems and occupational health risks that require proper enclosure and ventilation of pre-treatment areas.
Extremely High TDS — Biological Treatment Inhibition
TDS in combined tannery effluent typically ranges 5,000–20,000 mg/L after preliminary treatment, driven by sodium chloride from hide curing, sodium sulphate from dehairing chemicals, and tanning salts. High TDS above 3,000 mg/L inhibits biological treatment by raising osmotic stress on microorganisms. Dilution or TDS reduction through RO upstream of biological treatment is required for high-TDS tannery streams. CPCB's TDS discharge standard of <2,100 mg/L is frequently the most challenging parameter to achieve in tannery ETPs.
Sludge Volume and Hazardous Waste Disposal
Tannery ETPs generate very high sludge volumes: chrome sludge from precipitation (classified as Hazardous Waste under Schedule I, Category 34 under HWM Rules 2016), chemical sludge from physico-chemical treatment, and biological sludge from aerobic treatment. Combined sludge volumes of 5–15% of influent flow are typical. Chrome sludge must be disposed of at TSDF (Treatment, Storage, and Disposal Facility) — a significant ongoing OPEX cost. Chrome recovery reduces chrome sludge quantity by 80–90%, dramatically cutting hazardous waste disposal costs.
Colour Removal
Colour in tannery effluent comes from vegetable tannins (brown/yellow), synthetic dyes used in leather finishing (various colours), and melanoidin-type condensation products. While CPCB does not specify a numerical colour limit for tannery discharge, state PCBs increasingly require colour <200 ADMI in treated effluent. Colour removal requires supplementary treatment beyond biological processes — typically activated carbon adsorption, electrocoagulation, or ozone polishing at the tertiary stage.
ZLD Mandate in Key Clusters
State PCBs in Uttar Pradesh (Kanpur-Unnao) and Tamil Nadu (Ambur-Ranipet) are progressively mandating ZLD for tanneries in water-stressed areas. ZLD for tannery effluent is exceptionally challenging due to high TDS — downstream RO systems face rapid fouling and scaling from high-TDS, high-chloride, and high-sulphate brine. System design must include aggressive pre-RO softening, antiscalant dosing, and RO cleaning protocols. Concentrate from RO must be handled by MEE/MVR evaporation for final ZLD compliance.
Our Solutions
Tailored Wastewater Treatment Solutions
Chromium Recovery and Recycling System
Dedicated chrome recovery systems for segregated chrome tan liquor (Cr 2,000–8,000 mg/L): alkaline precipitation tank with caustic dosing to pH 8.5–9.0 → lamella clarifier → thickening → filter press → Cr(OH)₃ cake to re-dissolution tank with H₂SO₄ → reconstituted chrome tan liquor recycled to tanning drum. Typical chrome recovery >90%. Dramatically reduces chromium load in mixed effluent, hazardous chrome sludge generation, and chemical cost for downstream neutralisation.
Beamhouse Effluent Treatment
Segregated treatment for beamhouse (liming and dehairing) effluent: sulphide oxidation tank (air sparging or H₂O₂ dosing to reduce S²⁻ from 50–200 mg/L to <1 mg/L), hair recovery screen (hair collected for keratin recovery or disposal), pH correction (neutralisation of pH 12–14 alkaline beamhouse effluent), before combining with main ETP stream. Enclosed and ventilated design to prevent H₂S exposure.
Physico-Chemical Primary Treatment
Flash mixer, flocculation tank, and dissolved air flotation (DAF) for removal of suspended solids, residual fats and proteins, and remaining colloidal chromium from combined tannery effluent after stream-specific pre-treatments. Coagulant (alum or FeCl₃) and anionic polyelectrolyte dosing. DAF achieves TSS removal >80% and significant BOD reduction, protecting downstream biological treatment from overloading.
Extended Aeration / MBBR Biological Treatment
Aerobic biological treatment for dissolved BOD/COD reduction to CPCB discharge standards: BOD <30 mg/L, COD <250 mg/L. For tannery effluent with TDS <5,000 mg/L: extended aeration or MBBR. For higher TDS streams: MBBR with acclimatised halotolerant biomass. Aeration tank HRT 24–36 hours for tannery effluent (vs. 8–12 hours for food industry), reflecting the slower biodegradation of tannery-specific organics.
TDS Reduction and ZLD
For tanneries in ZLD-mandated zones: nano-filtration (NF) or RO for TDS reduction after secondary biological treatment. NF removes divalent ions (SO₄²⁻, Ca²⁺) selectively, reducing scaling potential for subsequent RO. RO permeate (TDS <500 mg/L) recycled to process. High-TDS RO/NF reject concentrated by MEE/MVR evaporation to 50–60% total solids for disposal. Salt recovery from evaporation concentrate for agricultural or industrial use where feasible.
Sludge Management
Integrated sludge management for tannery ETP: chrome sludge dewatered by filter press to 40–50% dry solids → stored in lined bay → transported to TSDF. Biological sludge dewatered by volute screw press to 18–22% DS. Separate sludge streams managed to avoid contaminating non-hazardous biological sludge with hazardous chrome sludge. Complete sludge characterisation, HWM Rule compliance, and disposal documentation.
Technologies
Proven Technologies for Your Industry
Benefits
Why Choose Spans for Your Industry
- Specialist tannery ETP expertise — one of India's most complex effluent profiles
- Chrome recovery system reducing hazardous waste disposal cost by 80–90%
- CPCB compliance: Total Chromium <2 mg/L, BOD <30 mg/L, TDS <2,100 mg/L
- Sulphide oxidation protecting biological treatment stability
- ZLD capability for Kanpur-Unnao and Ambur-Ranipet regulated clusters
- HWM Rule compliant sludge management design built into every project
- Turnkey EPC — process design, equipment, civil coordination, commissioning
- State PCB compliance support and environmental consent documentation
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