Bench-scale integrated bone and biochar bed treatment of geogenic fluoride contaminated groundwater from Bongo in Ghana

Abstract

The article explores the adsorption of fluoride in groundwater and the synergistic properties of a mixture of bone char and biochar. The bone char and biochar were produced using cattle bones and coconut husks, bamboo, neem tree and palm kernel in a locally constructed double-barrel retort with particle size ranging from 0.05 to 0.315 mm. The morphology of the char was examined using a scanning electron microscope and energy dispersive spectroscopy for elements. The surface functional groups were assessed by Fourier-transform infrared spectroscopy. Almost all the fluoride was removed from the groundwater within 15–27 min of column treatment. Cattle bone char standalone treatment was the most effective adsorbent, with a removal rate of 91.4%, which is almost identical to the integrated removal rate of 91.1% for bone char and coconut husk biochar. The presence of the hydroxyapatite groups in the bone char together with the high surface areas of the chars increased the integrated bed's effectiveness in lowering fluoride concentrations in contaminated groundwater from 3.6 mg/L to 1.5 mg/L with an adsorption capacity of 0.084 mg/g. The breakthrough curves were predicted with the bed depth service time model under the same operational conditions. The integrated bed showed almost 100% efficacy in removing fluoride from contaminated groundwater with a 3.6 mg/L fluoride concentration within a breakthrough time of 15–27 min. This was due to the interplay between the chars' high surface areas and the hydroxyapatite groups in the bone char, which enhance adsorption and the synergistic effect of the integrated char.