Use of CaO Loaded Mesoporous Alumina for Defluoridation of Potable Groundwater Containing Elevated Calcium Levels

Buddhika Gunawardana,Jagath Manatunge,Madhusha Sudasinghe,Achini Peiris,Mahesh Jayaweera

doi:10.3390/environments6060066

Abstract

Defluoridation in the presence of high calcium levels in potable groundwater is paramount, as the consumption of groundwater enriched with fluoride, and calcium has been implicated in causing chronic kidney disease of unknown etiology (CKDu) in Sri Lanka. CaO loaded mesoporous alumina (COMA) offers a great potential for defluoridation of potable water, but the effectiveness of COMA in the presence of calcium has not been investigated. This study, therefore, focuses on the investigation of the suitability of COMA for the defluoridation of potable water with high calcium levels. Mesoporous alumina was successfully functionalized with CaO to synthesize nano-level COMA with an optimum dosage for defluoridation being 2 g L−1. The amount of fluoride adsorbed increased (2.4–19.5 mg g−1) with the increase of the initial fluoride concentration (5–40 mg L−1), and the residual fluoride levels (0.8–1.47 mg L−1) were within the range specified by the WHO for drinking water. The amount of fluoride adsorbed by COMA varied between 6.50 and 7.97 mg g−1 with initial calcium levels between 0 and 1500 mg L−1, indicating that defluoridation was effective in the presence of high calcium levels. The fluoride adsorption was best fitted with the Langmuir model with a maximum monolayer capacity of COMA being 17.83 mg g−1, and adsorption kinetics fitted with the pseudo-2nd order model indicating strong covalent bonding by way of chemisorption. Thus, COMA can be effectively utilized as an adsorbent material in defluoridation efforts in areas prevalent with CKDu in the presence of high fluoride (15 mg L−1) and calcium (1500 mg L−1) levels.

Highlights

Fluoride in groundwater often occurs naturally by the dissolution of minerals in the soil
The peak intensities corresponding to the mesoporous alumina phase were found to decrease in the XRD pattern developed for CaO loaded mesoporous alumina (COMA) probably because of CaO loading
The amount of fluoride adsorbed by COMA varied between 6.50 and 7.97 mg g−1 with initial calcium levels between 0 and 1500 mg L−1 and higher percentages of removal

Summary

Introduction

Fluoride in groundwater often occurs naturally by the dissolution of minerals in the soil. Elevated fluoride levels in groundwater have been reported in many countries (in India, 48 mg L−1 [1]; in Mexico >6 mg L−1 [2]; in China >6 mg L−1 [3]; in Sri Lanka >13 mg L−1 [4]). Fluoride in groundwater combined with hardness has been implicated in causing a synergistic effect on chronic kidney disease of unknown etiology (CKDu). Fluoride levels of groundwater in areas prevalent with CKDu in Sri Lanka are in the range of 0.7 to 13.7 mg L−1 [4] along with average and maximum hardness levels of 293.4 to 1733.3 mg L−1 as CaCO3 , respectively [9]

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Conclusion