Wastewater Discharge Standards for Leather Tanning

Leather tanning generates highly polluted wastewater containing organic matter, chromium, sulfides, salts, and suspended solids. Before discharge into the environment or municipal sewer systems, this wastewater must be treated to meet stringent regulatory limits. Different jurisdictions have established their own standards, with China's GB 30486-2013 representing one of the most comprehensive frameworks.

China's GB 30486-2013 Standards

China's mandatory national standard for leather and fur making industry water pollutant discharge specifies limits for both conventional and characteristic pollutants.

Conventional pollutants: Chemical Oxygen Demand (COD) must be ≤80 mg/L for direct discharge (existing enterprises) and ≤200 mg/L for indirect discharge; Biochemical Oxygen Demand (BOD₅) ≤20 mg/L; Suspended Solids (SS) ≤50 mg/L; Ammonia Nitrogen ≤12 mg/L; Total Nitrogen ≤20 mg/L; Total Phosphorus ≤0.5 mg/L; pH within 6-9; Color ≤50 times; Oil and Grease ≤5 mg/L.

Characteristic pollutants: Total Chromium must be strictly controlled at <1.0 mg/L at the workshop discharge point and ≤1.5 mg/L at the final discharge point; Hexavalent Chromium (Cr⁶⁺) must be kept below detection limit (<0.1 mg/L); Sulfides ≤1.0 mg/L.

U.S. and International Standards

In the United States, the Environmental Protection Agency (EPA) has established BPT (Best Practicable Control Technology) limitations for leather tanning facilities, including BOD₅ ≤8.0 kg/kkg (daily maximum), TSS ≤11.6 kg/kkg, and Total Chromium ≤0.21 kg/kkg, with pH maintained between 6.0 and 9.0.

The EU's Best Available Techniques (BAT) conclusions for tanning recommend total chromium levels below 0.3-1 mg/L and sulfides below 1 mg/L for indirect discharges into urban wastewater treatment plants, achieved through chromium precipitation and sulfide oxidation techniques.

Compliance requires regular monitoring at designated sampling points — both workshop-level for characteristic pollutants like chromium and sulfides, and final discharge points for overall effluent quality. Zero Liquid Discharge (ZLD) systems are increasingly adopted by tanneries worldwide to fully recycle water and eliminate pollutant discharge. The ZDHC Wastewater Guidelines also provide unified requirements for the leather and footwear industry, covering sampling and testing protocols for direct, indirect, and zero liquid discharge scenarios.

Meeting these discharge standards protects aquatic ecosystems, prevents soil salinization, and safeguards public health from toxic heavy metal exposure.