Leather industry wastewater treatment addresses the highly complex effluent generated during hide processing. Tanneries produce concentrated pollutant loads from salting, liming, deliming, chrome tanning and dyeing operations.
Leather wastewater BOD reaches 1,500-6,000 mg/L, COD 3,000-12,000 mg/L and TDS 10,000-40,000 mg/L. Chromium (Cr+3) content is 50-500 mg/L and sulfide 200-3,000 mg/L. These levels make standard biological treatment impossible.
Arsistek leather industry solutions integrate chrome recovery unit, sulfide stripping column, chemical coagulation, equalization tank and activated sludge. Recovered chrome is returned to production — a major cost and environmental win.
Tannery Wastewater Characterization
Tannery effluent comes from three streams: wet operations (liming/deliming), tanning (chrome) and finishing (dyeing/oiling). Each stage has a distinct pollutant profile.
Wet operations effluent has high pH (10-12) and sulfide. Tanning effluent is low pH (3-4) and chrome-loaded. Dyeing effluent is colored, solvent-bearing and neutral pH.
Therefore stream segregation is mandatory: each is pretreated separately, then combined for biological treatment. Sulfide + acid generates explosive H2S — segregation is a safety requirement.
Chrome Recovery System
Chrome tanning effluent is collected separately and routed to the chrome recovery unit. pH is raised to 8-9 with MgO to precipitate Cr(OH)3.
The sludge is redissolved with H2SO4 and returned to production as chrome sulfate. Recovery efficiency is 80-95%.
Sulfide Oxidation
Liming wastewater is sulfide-rich. Catalytic air oxidation converts S²⁻ to SO₄²⁻.
Manganese or iron salts catalyze the reaction. 2-6 hours contact time removes 95%+ sulfide, preventing downstream H2S formation.
Multi-Stage Process Design
Tannery WWTP has 5 main stages:
- Stream segregation: Chrome, sulfide and general streams collected separately
- Pretreatment: Chrome recovery, sulfide oxidation, screening, grit chamber
- Chemical: Coagulation-flocculation, primary clarification
- Biological: Activated sludge or MBR with halophile adaptation
- Tertiary: Sand filter, activated carbon, ozone if needed
Leather Sector Solution Advantages
Leather Industry References
Our tannery WWTP reference projects.
Frequently Asked Questions
Not legally required in Turkey but strongly recommended due to chromium cost and toxicity. 80-95% recovery efficiency achievable.
Mixing sulfide-rich liming and acidic chrome tanning effluents produces toxic, explosive H2S. Segregation is a safety requirement.
Standard activated sludge loses efficiency above 5,000 mg/L. We use halophilic culture or MBR with high MLSS. Salt dilution is an alternative.
Direct discharge with chrome/sulfide is prohibited. Pretreatment to meet zone inlet limits is required.
COD < 800, BOD < 250, TSS < 200, Cr < 1, S < 1 mg/L per Turkish leather industry discharge regulation (SKKY Table 9).
0.5-1.2 kg DS/m³ daily. Dewatered to 20-30% solids with belt-press/decanter and sent to licensed disposal. Post-chrome-recovery sludge is less hazardous.