CPCB Effluent Discharge Standards for Tanneries — Explained

About This CPCB Standard

Tanneries are one of the 17 Grossly Polluting Industries (GPI) identified by CPCB. Effluent discharge standards for tanneries are prescribed under the Environment (Protection) Rules 1986, Schedule I, notified by the Ministry of Environment, Forest and Climate Change through GSR notifications under the Environment Protection Act 1986.

CPCB has specific standards for individual tanneries discharging independently, and separate standards applicable to Common Effluent Treatment Plant Operators (CETPOs) serving tannery clusters. Tannery clusters in Kanpur (Uttar Pradesh), Vellore and Ambur (Tamil Nadu), Kolkata (West Bengal), and Jalandhar (Punjab) are subject to CETP mandates under directions from CPCB and respective State Pollution Control Boards.

Why Tanneries Face India's Strictest Effluent Rules

Tannery wastewater is among the most complex and hazardous industrial effluents in India. The combination of chemical pollutants, high organic load, and sheer volume of salt-bearing water creates a treatment challenge that very few other industries match. There are four primary reasons tanneries face such strict regulation:

• Chromium from chrome tanning — Chrome tanning uses chromium sulphate (Cr₂(SO₄)₃) as the tanning agent. Residual trivalent chromium in effluent, and any Cr⁶⁺ formed under oxidising conditions, is extremely toxic to aquatic ecosystems and is a known human carcinogen at hexavalent form. Even small carryover from spent chrome liquors causes Cr⁶⁺ exceedances in final effluent.
• Sulphide from unhairing and liming — Sodium sulphide (Na₂S) and lime are used in the beamhouse for unhairing and de-fleshing. Sulphides in effluent cause hydrogen sulphide (H₂S) gas odour at low pH and are acutely toxic to aquatic organisms even at low concentrations. Sulphide treatment must precede biological treatment or the biology collapses.
• TDS from sodium chloride (NaCl) — Common salt is used for hide preservation before tanning. NaCl contributes 5,000–15,000 mg/L TDS to raw tannery effluent, creating severe Zero Liquid Discharge (ZLD) challenges. Standard ETP cannot remove dissolved salts — membrane systems or evaporation are required.
• High BOD and COD from organic matter — Flesh, hair, fat, and protein residues from hides drive extremely high organic load. BOD of 1,500–4,000 mg/L in raw effluent is common, requiring multiple stages of biological treatment to reach the discharge standard of ≤30 mg/L.

The combination of these four streams — chrome, sulphide, salt, and organics — is why tannery wastewater is classified among the most complex in Indian industry, and why CPCB treats tanneries as Grossly Polluting Industries requiring the highest level of oversight.

Tannery Effluent Discharge Limits at a Glance

The following table summarises CPCB's prescribed effluent discharge standards for tanneries under the Environment (Protection) Rules 1986. Two disposal routes are covered: discharge to inland surface water (rivers, canals, lakes) and land disposal (irrigation or land application).

The Cr⁶⁺ limit of 0.1 mg/L and the TDS limit of 2,100 mg/L are consistently the two most difficult parameters for tanneries to achieve. They drive the most significant process design decisions in tannery ETP and CETP systems.

Chromium Rules — Cr⁶⁺ vs Total Chromium

Chrome tanning accounts for approximately 80–85% of leather production in India. The process uses chromium sulphate (Cr₂(SO₄)₃) — trivalent chromium — which is far less toxic than hexavalent chromium (Cr⁶⁺). However, CPCB regulates both forms because trivalent chromium can oxidise to Cr⁶⁺ in certain conditions.

The Cr⁶⁺ limit of 0.1 mg/L is extremely strict. This is a known carcinogen classification limit — at this concentration, even small amounts of chrome carryover from spent tanning baths cause exceedances. Key compliance requirements for chrome management:

• Chrome recovery tanks are mandatory — spent chrome liquor from tanning drums must be collected in dedicated recovery tanks and not discharged with general effluent. Chrome precipitation is carried out by raising pH to 8.5–9.0 with NaOH or lime, which precipitates chromium as Cr(OH)₃ sludge (chrome cake).
• Chrome cake is hazardous waste — Cr(OH)₃ sludge is classified as hazardous waste under the Hazardous and Other Wastes (Management and Transboundary Movement) Rules 2016. It must be sent to an authorised Treatment, Storage and Disposal Facility (TSDF) with a hazardous waste manifest. Landfilling chrome cake on-site is illegal.
• Total Chromium ≤2.0 mg/L is achievable — with a well-operated chrome precipitation unit and pH control, total chromium in final effluent can be brought well below 2.0 mg/L. The challenge is Cr⁶⁺ at the 0.1 mg/L threshold, which requires complete segregation of chrome streams.
• Segregation of chrome and vegetable tanning streams — tanneries using both chrome and vegetable tanning must maintain completely separate drain systems for the two streams. Cross-contamination of vegetable tanning liquors (which may contain oxidising agents) with chrome streams is a route to Cr⁶⁺ formation.
• Regular chrome bath monitoring — spent chrome bath concentration must be measured before reuse or discharge. Maintaining a chrome bath log is good practice and increasingly expected by SPCBs during inspections.

Sulphide and TDS — The Hidden Compliance Challenges

While chromium receives the most regulatory attention, sulphide and TDS create the most persistent day-to-day compliance problems for tannery ETPs.

Sulphide from liming: Sodium sulphide (Na₂S) used in the unhairing and liming stage produces effluent with sulphide concentrations of 200–500 mg/L — 100 times the CPCB discharge limit of ≤2.0 mg/L. At low pH, dissolved sulphide converts to H₂S gas, which is toxic, corrosive to concrete, and creates serious odour complaints from surrounding communities. The treatment sequence requires:

• H₂S stripping under controlled alkaline conditions (not at low pH, which would volatilise H₂S directly to atmosphere)
• Chemical oxidation using aeration combined with iron salts (FeSO₄ or FeCl₃) to convert sulphide to sulphate before the effluent enters the biological treatment stage
• Biological treatment cannot function properly with high sulphide — it inhibits aerobic microorganisms. Sulphide pre-treatment is a prerequisite for effective biological oxidation of BOD.

TDS from NaCl: The 2,100 mg/L TDS limit is the most capital-intensive compliance challenge in tannery treatment. Raw effluent TDS from hide curing salt typically falls in the range of 5,000–15,000 mg/L — three to seven times the limit. Biological treatment and conventional clarification cannot remove dissolved salts. Achieving the TDS limit requires:

• Nanofiltration (NF) or reverse osmosis (RO) membranes to physically reject dissolved salts from the treated effluent stream
• In CETP schemes, multi-effect evaporators (MEE) or mechanical vapour recompression (MVR) units for NaCl recovery are being mandated in some states, particularly under ZLD requirements imposed by Tamil Nadu SPCB and UP SPCB
• NaCl recovered from MEE can in principle be recycled for hide curing, reducing raw material costs — though quality and logistics constraints limit this in practice

The TDS compliance requirement is one of the primary drivers pushing tannery clusters toward CETP-based ZLD systems rather than individual ETPs, since the capital cost of NF/RO or MEE is more efficiently shared across multiple tanneries in a cluster.

CETP Obligation for Tannery Clusters

CPCB and state SPCBs require individual tanneries in notified clusters to connect to a Common Effluent Treatment Plant (CETP). This is a regulatory direction, not merely a recommendation — individual tanneries in cluster zones may not be permitted to discharge independently even if they operate a technically adequate individual ETP.

The following clusters are under CETP mandates with active SPCB monitoring of inlet quality and discharge performance:

• Kanpur — Jajmau cluster (Uttar Pradesh) — One of India's largest tannery concentrations, discharging to the Ganga river basin. Under NGT scrutiny following chromium contamination incidents. UP SPCB monitors CETP inlet quality from individual tanneries.
• Vellore, Ambur, and Ranipet (Tamil Nadu) — Tamil Nadu SPCB has imposed strict CETP connectivity requirements. TNPCB monitoring of individual tannery inlet contributions is stringent, with units found contributing excess chrome or sulphide facing individual closure action even within a CETP framework.
• Kolkata — Tangra and Tiljala (West Bengal) — Leather processing units connected to CETP under West Bengal PCB directions.
• Jalandhar (Punjab) — Cluster under Punjab PCB oversight.

CETPOs are required to achieve the same discharge limits as individual tanneries. They are additionally required to monitor and control the quality of effluent received from member tanneries — an inlet quality standard is effectively imposed on each contributing tannery by the CETPO.

Tanneries considering new investment in an individual ETP in a notified cluster area should verify current SPCB directions before committing capital. In several cluster zones, individual ETP discharge permits are no longer being granted irrespective of treatment performance.

Monitoring, OCEMS and Testing Requirements

Tanneries are classified as Red Category industries under CPCB's industry categorisation. This classification carries the highest level of monitoring obligation:

• OCEMS mandatory — Online Continuous Effluent Monitoring Systems must be installed and connected to SPCB and CPCB servers. Minimum parameters monitored continuously: pH, flow rate, COD, and total chromium — at both the inlet and outlet of the ETP. Real-time data transmission to the SPCB server is a consent condition for Red Category units. Failure to maintain OCEMS connectivity is itself a compliance violation.
• Quarterly NABL lab testing — Quarterly testing by a NABL-accredited laboratory is the minimum frequency for comprehensive effluent characterisation, covering all consent parameters including sulphides, TDS, ammoniacal nitrogen, and heavy metals beyond chromium if relevant.
• Annual sludge characterisation — Chrome cake sludge and other ETP sludges must be characterised annually for chromium content and other hazardous constituents. This drives the TSDF disposal requirement and manifest documentation.
• TSDF disposal with manifest — All chrome cake and metal-bearing sludges must be disposed of at an authorised TSDF. Each consignment requires a hazardous waste manifest under the HW Rules 2016. Records of all manifest transactions must be maintained and available for SPCB inspection.
• Form V annual return — Environmental compliance annual return (Form V under the Environment Protection Act) must be submitted to the SPCB by 31 January each year, covering the previous calendar year's effluent monitoring data, hazardous waste generation, and disposal records.

Penalties for Non-Compliance

Non-compliance with tannery effluent standards has resulted in some of the most severe regulatory enforcement actions in Indian environmental law:

• Kanpur Jajmau — NGT closure orders — Chromium discharge from tanneries to the Ganga river basin has resulted in National Green Tribunal directions for closure of non-compliant tanneries. Multiple Kanpur tanneries have faced closure notices following CPCB inspection findings.
• Vellore — blanket closure orders in 2024 — Chrome contamination of groundwater in Vellore and surrounding districts led to blanket closure orders affecting multiple tanneries. Groundwater chromium contamination is treated as an acute environmental emergency by both NGT and TNPCB.
• Environment Protection Act Section 15 penalties — Discharge in violation of CPCB/SPCB consent limits is an offence under Section 15 of the Environment Protection Act 1986, carrying penalties of up to 5 years imprisonment and a fine of ₹1 lakh for a first offence, plus a continuing daily fine for each day the violation persists after conviction. Directors and responsible officers of companies are personally liable under these provisions.
• Consent suspension and closure direction — State PCBs can issue directions under Section 5 of the EPA 1986 to close, prohibit, or regulate any industrial operation found in violation. Consent to Operate (CTO) suspension effectively halts production until compliance is demonstrated.

The tannery sector has been a priority enforcement target for CPCB and the NGT since the 2010s, driven by Ganga basin pollution and groundwater contamination concerns in Tamil Nadu. The regulatory risk of chromium non-compliance for tanneries is therefore not theoretical — it is demonstrated by actual enforcement action resulting in unit closures and criminal proceedings.