Sustainable wastewater treatment by banana peel/layered double hydroxide composite under ideal conditions using the Taguchi method

The present study investigates the removal of the cationic dye crystal violet (CV) from aqueous solutions using low-cost adsorbents derived from agricultural waste. Banana peels (BP) were activated, and a Ni–Ca–Fe layered double hydroxide (LDH) as well as a BP/LDH composite were synthesized and applied as adsorbents. The Taguchi experimental design was employed to optimize the adsorption process parameters, including pH, adsorbent dose, contact time, and initial dye concentration. Among the studied factors, pH, adsorbent dose, and initial concentration exhibited the most significant influence on CV removal efficiency. Under optimal conditions (pH 9, adsorbent dosage 0.1 g/L, and contact time 120 min), removal efficiencies of 66.0, 82.4, and 95.2% were achieved for BP, LDH, and BP/LDH, respectively. Analysis of variance (ANOVA) revealed that pH was the most influential parameter for CV adsorption onto BP and BP/LDH, whereas contact time played the dominant role for LDH. Equilibrium data were well described by the Freundlich, Langmuir, and Temkin isotherm models, with maximum adsorption capacities of 39.16, 81.10, and 187.40 mg/g for BP, LDH, and BP/LDH, respectively. Kinetic studies showed that the adsorption process followed the pseudo-second-order model, indicating chemisorption as the dominant mechanism. Reusability tests demonstrated that the BP/LDH composite retained a high removal efficiency of 80.0% after four adsorption – desorption cycles. These findings confirm that the BP/LDH composite is an efficient, sustainable, and reusable adsorbent with strong potential for practical wastewater treatment applications.