Abstract
This study investigated the removal of fluoride from water using a calcium-modified dairy manure-derived biochar (Ca-DM500). The Ca-DM500 showed a 3.82 - 8.86 times higher removal of fluoride from water than the original (uncoated) manure-derived biochar (DM500). This is primarily attributed to strong precipitation/complexation between fluoride and calcium. The Freundlich and Redlich-Peterson sorption isotherm models better described the experimental data than the Langmuir model. Additionally, the removal kinetics were well described by the intraparticle diffusion model. The Ca-DM500 showed high reactivity per unit surface area [0.0001, 0.03, 0.16 mg F per m2 for Douglas fir-derived biochar (DF-BC), DM500. and Ca-DM500, respectively] for retention of fluoride reflecting the importance of surface complexation. The copresence of anions reduced removal by Ca-DM500 in the order SO2−4≈PO3−4>NO−3SO42-≈PO43->NO3-<math> <mrow> <msubsup><mrow><mtext>SO</mtext></mrow> <mn>4</mn> <mrow><mn>2</mn> <mo>-</mo></mrow> </msubsup> <mo>≈</mo> <msubsup><mrow><mtext>PO</mtext></mrow> <mn>4</mn> <mrow><mn>3</mn> <mo>-</mo></mrow> </msubsup> <mo>></mo> <msubsup><mrow><mtext>NO</mtext></mrow> <mn>3</mn> <mo>-</mo></msubsup> </mrow> </math> . The sorption behavior of fluoride in a continuous fixed-bed column was consistent with the Thomas model. Column studies demonstrated that the Ca-DM500 shows a strong affinity for fluoride, a low release potential, and a stable (unreduced) removal capacity through regeneration and reuse cycles.