Treatment Methods for Leather Wastewater

Leather manufacturing generates complex wastewater containing high levels of organic pollutants, heavy metals (especially chromium), sulfides, salts, and suspended solids. Effective treatment requires multi-stage processes:

1. Primary Treatment:

Screening & Equalization: Removal of solid debris and flow/load balancing.

Chemical Coagulation/Flocculation: Aluminum or iron salts precipitate suspended solids and colloids.

Sedimentation: Sludge separation via clarifiers.

2. Secondary Treatment:

Biological Processes:

Aerobic Treatment (e.g., activated sludge): Degrades organic matter using bacteria.

Anaerobic Treatment (e.g., UASB reactors): Breaks down high-COD load and recovers biogas.

Sulfide Oxidation: Air injection converts toxic sulfides to less harmful sulfates.

3. Tertiary/Advanced Treatment:

Chromium Recovery: Alkaline precipitation (pH 8–9) isolates chromium as Cr(OH)? sludge for reuse.

Membrane Filtration: Reverse osmosis (RO) or nanofiltration (NF) removes dissolved salts and residual metals.

Advanced Oxidation Processes (AOPs): Ozone/UV or Fenton’s reagent degrades persistent organics.

4. Sludge Management:

Dewatering (centrifuges/filter presses) and safe disposal (landfill) or thermal drying for energy recovery.

Modern plants prioritize water recycling (e.g., membrane-treated water for rinsing) and chromium reuse. Zero-liquid discharge (ZLD) systems, though costly, eliminate effluent by crystallizing salts.

Combining these methods ensures compliance with discharge standards (e.g., COD < 200 mg/L, Cr < 1 mg/L) while minimizing environmental impact.