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

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.