Sustainable valorization of waste-derived adsorbents for textile RO brine pre-treatment via adsorption and UF hybrid systems

Reverse osmosis (RO) is widely employed for advanced treatment of textile wastewater, typically achieving around 80% water recovery, while the remaining brine still poses management challenges. This study explores the use of waste-derived adsorbents, sawdust-based activated carbon (ACs), calcined eggshells (CES), and commercial activated carbon (CAC), for the removal of dyes and chemical oxygen demand (COD) from textile RO brine. Material characterization using BET, XRD, FTIR, and surface charge analysis revealed that ACs and CAC have high surface areas, porous structures, and abundant surface functionalities, which account for their superior adsorption performance, whereas CES was less effective under high salinity conditions. Batch experiments demonstrated that ACs achieved the highest removal efficiencies, with 92% dye and 62% COD reduction at 400 mg/L. Integrating ACs with ultrafiltration (UF) in a hybrid system further improved treatment performance, achieving complete dye removal and 82% COD reduction with only 150 mg/L of adsorbent. The dynamic AC layer formed on the membrane stabilized permeate flux (>80 L/m 2 /h 1 ) and shifted fouling toward a predominantly reversible regime, easily mitigated by water rinsing. This hybrid ACs/UF approach enhances treatment efficiency, prolongs membrane lifespan, and demonstrates a sustainable strategy for valorizing waste-derived materials in water recycling within the textile industry.