Treatment of Leather Industry Wastewater Using Coagulation, Ultraviolet/Persulfate Processing and Nanofiltration for Water Recovery

This study investigated water recovery with the treatment of leather industry processes wastewater (washing, pickling, and degreasing units) using coagulation, ultraviolet/persulfate (UV/PS) treatment, and nanofiltration processes. Coagulation studies were carried out using alum as the coagulant, and the highest chemical oxygen demand (COD) removal efficiency was obtained at pH 7 for all the wastewater. The highest COD and total organic carbon (TOC) removal were 80.9 and 50.5% in the wastewater washing unit (\({{{\text{S}}}_{{\text{2}}}}{\text{O}}_{8}^{{2 - }}\) : 8 g/L, pH 7) and 76.5 and 96.1% in the wastewater degreasing unit (\({{{\text{S}}}_{{\text{2}}}}{\text{O}}_{8}^{{2 - }}\) : 16 g/L, pH 6) using UV/PS oxidation, respectively. High COD and TOC removal could not be achieved with UV/PS oxidation in the wastewater pickling unit. In the studies performed with NP030 nanofiltration membrane after UV/PS oxidation, the highest permeability and COD removal was achieved at pH 7 under 4 × 10⁵ Pa pressure in wastewater washing and degreasing units. After 75 min of nanofiltration at pH 7 in washing and degreasing units, the total filtrate amount was 39.8 and 42.3 L/m² h, respectively. COD concentration in the wastewater washing unit decreased from 4434 to 138 mg/L, while it decreased from 5833 to 212 mg/L in the wastewater degreasing unit with coagulation, UV/PS processing, and nanofiltration. As a result, the treatment of leather industry wastewater through separate streams with coagulation, UV/PS, and nanofiltration, washing, and degreasing unit wastewater provides very high COD removal. Also, it has been shown impossible to treat the pickling unit wastewater by UV/PS oxidation.