Treatment of water from the textile industry contaminated with indigo dye: A hybrid approach combining bioremediation and nanofiltration for sustainable reuse

In recent decades, the extensive use of synthetic dyes in dye-based industries, particularly the textile sector, has led to environmental contamination, raising concerns about water quality and human health. This study aimed to develop a sustainable approach for treating wastewater contaminated with indigo dye through a hybrid approach combining bioremediation and nanofiltration for reuse. In the first stage, two bioaugmentation strategies were compared: using native microorganisms in the wastewater (R-1) and activated sludge from a municipal wastewater treatment plant (R-2). Both strategies effectively reduced chemical oxygen demand (COD) to 200 mg/L and eliminated over 90% of the color. Statistical analysis showed no significant difference in COD removal efficiencies between R-1 and R-2. Correlation analysis revealed a strong association (>99%) between COD, suspended solids (SS) concentration, and color in the reactors, providing insights into sustainable monitoring for wastewater treatment, with potential cost reductions and environmental benefits. In the second stage, nanofiltration (NF) with organic membranes was employed to obtain high-quality permeate for reuse in denim washing. Permeability measurements for R-1 demonstrated similar membrane behavior (NF 270 and Alfa Laval NF) at various transmembrane pressures (TMPs). Both membranes achieved color rejection rates exceeding 96% and COD removal efficiency over 80% for all TMPs. NF tests with R-2 effluent revealed higher permeate flux of 23.71 L·h−1·m−2 at a TMP of 5 bar, with Alfa Laval NF membrane exhibiting superior COD and color rejection compared to NF 270 membrane. The techno-economic analysis showed the hybrid approach of biological treatment/NF to have a mean unit cost of 0.97 USD/m3, indicating economic feasibility and competitiveness against commercial purification processes for sustainable water reuse.