Simplified Batch and Fixed-Bed Design System for Efficient and Sustainable Fluoride Removal from Water Using Slow Pyrolyzed Okra Stem and Black Gram Straw Biochars

[Image: see text] Okra stem biochar (OSBC) and black gram straw biochar (BGSBC) were prepared by slow pyrolysis at 500 and 600 °C, respectively. OSBC and BGSBC were characterized using S(BET), Fourier transform infrared, X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, SEM–energy dispersive X-ray, and energy dispersive X-ray fluorescence. High carbon contents (dry basis) of 66.2 and 67.3% were recorded in OSBC and BGSBC, respectively. The OSBC surface area (23.52 m(2)/g) was higher than BGSBC (9.27 m(2)/g). The developed biochars successfully remediate fluoride contaminated water. Fluoride sorption experiments were accomplished at 25, 35, and 45 °C. Biochar-fluoride adsorption equilibrium data were fitted to Langmuir, Freundlich, Sips, Temkin, Koble–Corrigan, Radke and Prausnitz, Redlich–Peterson, and Toth isotherm models. The sorption dynamic data was better fitted to the pseudo-second order rate equation versus the pseudo-first order rate equation. The Langmuir sorption capacities of Q(OSBC)(0) = 20 mg/g and Q(BGSBC)(0) = 16 mg/g were obtained. Biochar fixed-bed dynamic studies were accomplished to ascertain the design parameters for developing an efficient and sustainable fluoride water treatment system. A column capacity of 6.0 mg/g for OSBC was achieved. OSBC and BGSBC satisfactorily remediated fluoride from contaminated ground water and may be considered as a sustainable solution for drinking water purification.