CMC-based nanofiltration membranes for treatment of dye-contaminated wastewater

Eco-friendly carboxymethyl cellulose (CMC)-based membranes were fabricated on polyethersulfone (PES) support membranes by incorporating a lactic acid (LA) coating layer as a non-toxic and sustainable surface modification strategy. The separation performance of the fabricated membranes was evaluated for the treatment of dye-contaminated wastewater using a laboratory-scale cross-flow nanofiltration (NF) system. The membranes demonstrated effective removal of Congo red (CR), crystal violet (CV), and methylene blue (MB), with rejection efficiencies exceeding 95% for CR, approximately 90% for CV, and approximately 86% for MB. The fabricated membranes were comprehensively characterized by field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and contact angle measurements. Correlation of the physicochemical characteristics with the permeation flux and separation performance revealed that the membrane containing 0.2 wt% CMC and coated with 0.25 wt% LA exhibited the optimum overall performance. In addition to excellent dye rejection, the optimized membrane demonstrated effective separation of divalent salts, achieving rejection efficiencies of approximately 57% for MgSO₄ and 26% for Na₂SO₄ at an applied pressure of 3 bar. The rejection of dyes and salts was primarily attributed to size exclusion and Donnan exclusion mechanisms. Furthermore, antifouling evaluation demonstrated a relatively low fouling tendency of the CMC-based membranes, with the optimized membrane exhibiting a high flux recovery ratio (FRR) of approximately 88.6%. Overall, the results demonstrate that LA-modified CMC-based membranes provide a promising, environmentally friendly, and sustainable alternative for the efficient treatment of dye- and salt-contaminated wastewater.