Indigo dyeing wastewater reclamation by membrane-based filtration and coagulation processes

In the present study, the possibility to reuse the indigo dyeing rinsing wastewater originating from a denim textile mill was investigated. Coagulation and filtration processes were selected as the pretreatment alternatives and applied to dyeing wastewater samples. Both physicochemical pretreatment alternatives and nanofiltration technique were optimized to produce an effluent satisfying the reuse criteria for the textile industry. The results showed that coagulation is not an effective and efficient pretreatment due to high dose of coagulant requirement. Microfiltration (MF) through 0.45 mm pore-sized membrane provided 64% removal in color and 29% removal in COD leading to a color value of 2493 Pt-Co and COD of 892 mg/L in the permeate. Furthermore, ultrafiltration (UF) applied after MF revealed additional 62% color and 4% COD removals leading to a color value of 960 Pt-Co and COD of 856 mg/L. Hence, the sequential application of MF and UF and only MF as pretreatment alternatives were found to be promising prior to the application of nanofiltration (NF). NF experiments conducted using pretreated wastewater via only MF provided 99% color and 97% COD removals leading to a color of 15 Pt-Co and a COD of 20 mg/L and hence sequential application of MF and NF was found to be the optimum treatment scheme for the reuse of the dyeing wastewater of the studied textile mill and reuse criteria was satisfied.