Optimization, Characterization and Modeling of Functionalized Macadamia Nutshell Derived-Biochar for Drinking Water Defluoridation

Abstract

Fluoride contamination in drinking water is a serious global environmental concern owing to its irreversible health effects. This study synthesized Zr(IV)-impregnated macadamia nutshell biochar (Zr-MNSB) by the surface modification of macadamia nutshell biochar (MNSB) and investigated its fluoride removal efficiency and biosorption capacity. Surface modification significantly enhanced the specific surface area and pore size. FE-SEM results exhibited increased porosity with Zr(IV)-impregnation and EDX confirmed Zr(IV) existence on the MNSB surface which enhanced fluoride removal performance. The effect of pH, co-existing ions, biosorbent dosage, contact time, and initial fluoride concentration were investigated using batch experiments. Zr-MNSB showed stable and excellent fluoride removal efficiency (78–99%) with initial fluoride concentration of 10 mg L–1 at a pH range of 2–8 compared to MNSB with 77.78% removal efficiency at pH 2 which declined significantly with pH increase. Zr-MNSB defluorinated naturally contaminated water below the WHO standard (1.5 mg L–1). The Langmuir isotherm fitted well the experimental results with high R2 (0.98) compared to the investigated isotherms and it exhibited maximum fluoride biosorption capacity of 11.97 mg g–1. The pseudo-second-order kinetic model best suited the experimental results with high R2 (≈1.0). The thermodynamic parameters viz., ΔH°, ΔS° and ΔG° revealed that the fluoride removal process was endothermic, irreversible, random, spontaneous, rapid, and chemisorption in nature. Regenerated Zr-MNSB exhibited stable removal efficiency of 72–89% for three cycles but dropped significantly to 47% after the 4th cycle. Thus, this study developed a simple, affordable and efficient biosorbent that’s potential for drinking water treatment.