Sustainable treatment of textile wastewater using spent tea waste adsorbent: Optimization, isotherm and kinetics modelling

This study demonstrates the valorization of spent tea waste into a low-cost biochar adsorbent for the treatment of real textile industry wastewater. In contrast to conventional studies that focus on synthetic dyes, this work addresses complex, real-world industrial effluents, offering a practical and scalable solution for mitigating water pollution. Comprehensive characterization using FTIR, SEM, and EDX indicated the presence of key functional groups (–OH, C=C, C–O) and a porous, heterogeneous surface morphology, which facilitate dye adsorption primarily through physisorption mechanisms such as electrostatic attractions, hydrogen bonding, and π–π stacking with minor contributions from ion exchange. Process optimization via Response Surface Methodology (RSM) identified adsorbent dosage as the most influential operational parameter. Under optimal conditions 3.54 g of biochar, 30 minutes of contact time, and agitation at 510 rpm, the model predicted a dye removal efficiency of 81.35%, which was experimentally validated at 90.19%. The treatment significantly enhanced wastewater quality, achieving 85.75% color reduction, 62.88% COD removal, and 90.55% zinc removal. Nevertheless, certain effluent parameters remained above national discharge limits, indicating the need for complementary treatment stages. Adsorption isotherm and kinetic analyses revealed multilayer physisorption on a heterogeneous surface, best represented by the Freundlich model (R 2 = 0.941), and a rate-controlling mechanism consistent with pseudo-second-order kinetics (R 2 = 0.998). Reusability tests demonstrated a gradual decline in adsorption efficiency over three cycles, underscoring the necessity for more robust regeneration strategies. Overall, biochar derived from spent tea waste presents a sustainable, low-cost, and environmentally sound option for primary treatment of textile wastewater, effectively integrating waste valorization with pollution control particularly in regions where tea waste is abundantly available. • The influence of fire outbreaks from sugar refinery industry has been investigated on nearby river water quality. • The degree of contamination using various water quality parameters and indices was utilized to evaluate corresponding risks to aquatic life. • Different pollution indices, including MI, HPI, RPI, OPI, and ROPI, showed serious contamination of the river. • The elevated level of contamination poses severe risks to aquatic life and the surrounding ecosystem.