Optimization studies for water defluoridation by adsorption: application of a design of experiments

Abstract

Fluoride in groundwater is a worldwide problem. In Tunisia, it is one of the most abundant constituents occurring in groundwater, creating a major problem in safe drinking water supply. This paper aims to examine the fluoride removal from aqueous solutions by adsorption on activated alumina (AA) using a two-level full factorial design. For this sake, four operating parameters supposed to affect the removal efficiency were chosen: initial fluoride concentration, pH of the solution, adsorbent dose, and temperature. Factors that influence the fluoride removal efficiency were evaluated statistically by using factorial plots: the Pareto chart, main effect, interaction effect, normal probability plots, and the cube plot. Analysis of variance and P-value significant levels were used to check the significance of the effect on percentage removal. The statistical analysis allowed verifying that the four studied parameters have an influence on the fluoride elimination (P-values ≤0.05 and F-values >4.49). It was found that increasing adsorbent dose enhances significantly the fluoride removal efficiency (from 62.3 to 98.4%). In the second part of the study, suitability of AA for natural waters defluoridation was investigated. The technical viability of the process was verified in the case of groundwater sample as the percentage removal reached 76.3% at optimal conditions.

Keywords:

• Fluoride removal
• Adsorption
• Water treatment
• Alumina
• ANOVA
• Factorial design