Acid‐activated water hyacinth ( Eichhornia crassipes ) from the Nile River for textile wastewater reclamation: A comparative evaluation of anionic and cationic dye adsorption

Water hyacinth ( Eichhornia crassipes ) is an extremely invasive aquatic plant with notable environmental and socioeconomic impacts; however, its unique physicochemical properties offer potential for wastewater treatment through adsorption. This study investigates the acid activation of water hyacinth using acetic, sulphuric, hydrochloric, and nitric acids to enhance its performance as an adsorbent for dye removal. The aquatic plant was harvested from the Nile River, processed, and activated with each acid, and a comparative evaluation was performed. Adsorption efficiency was assessed using Methylene Blue (cationic) and Ponceau S (anionic) dyes, with removal percentage determined by spectrophotometric analysis before and after treatment. Sulphuric acid activation produced the highest adsorption capacity, achieving 94.5% removal for Ponceau S and 98.7% for Methylene Blue, attributed to improved surface area and pore structure. Response surface methodology was applied to model the effects of adsorbent dosage, contact time, and dye concentration while maximising adsorption capacity. The adsorption data were fitted to the Langmuir, Freundlich, and Dubinin–Radushkevich isotherms, and adsorption kinetics were evaluated. Sulfonated water hyacinth showed strong conformity with the Langmuir isotherm ( R 2 = 0.99, q m = 4.275 mg g −1 ) and the Dubinin–Radushkevich model ( R 2 = 0.844, Q D = 5.09 mg g −1 ), indicating monolayer adsorption and reliable model fit. Kinetic modelling followed the pseudo‐second‐order model, suggesting that chemisorption was the dominant mechanism. Overall, the study demonstrates the high potential of water hyacinth‐derived adsorbents as sustainable materials for wastewater treatment.