A practical approach on reuse of drinking water treatment plant residuals for fluoride removal.

The sustainable management of the voluminous waste from drinking water treatment plants has motivated environmental researchers towards several reuse options. Water treatment residues (WTR) are proven adsorbent for remediation of many water- and soil-borne anions (perchlorate, selenium and arsenic), and may be able to remove fluoride from contaminated water. In this study, the sustainable reuse of the freely available waste of the drinking water treatment plants, namely WTR, was explored for their fluoride removal potential to meet drinking water standards. WTR was characterized by specific surface area, Fourier transform infrared (FT-IR), scanning electron microscopy and X-ray powder diffraction (XRD). Batch adsorption experiments were conducted as a function of WTR dose, contact time, agitation speed, initial fluoride concentration, initial temperature and water pH to get best adsorption capacity. About 90% fluoride removal (from initial 5.0 mg/L) was observed within 2 h contact time at WTR dose of 28 g/L. Also, WTR effectively removed fluoride in the pH range of 5-8, whereas removal efficiency decreased at pH 9 or higher. The adsorption equilibrium was established within 120-150 min. Adsorption isotherm data were best fit to Langmuir (R2 = 0.984) and Freundlich models (R2 = 0.983), while adsorption kinetic study exhibited that second-order kinetic model was followed with rate constant of 0.038 g/mg min. The FT-IR and XRD analyses affirmed that the metal hydroxyl and metal oxide groups contributed to the fluoride removal. The experimental results show the promising potential of WTR as an adsorbent in fluoride removal from real contaminated groundwater.