Fabrication of Metal Oxide-Biopolymer Nanocomposite for Water Defluoridation

Fabrication of Metal Oxide-Biopolymer Nanocomposite for Water Defluoridation

Dickson Mubera Andala (Multimedia University of Kenya, Kenya), Erick Mobegi (Kenyatta University, Kenya), Mildred Nawiri (Kenyatta University, Kenya) and Geoffrey Otieno (Technical University of Kenya, Kenya)
DOI: 10.4018/978-1-7998-1871-7.ch013

Abstract

Fluoride contamination in groundwater affects about 150 million people worldwide. In this study, the authors focused on synthesizing biopolymer metal oxide nanocomposite for fluoride removal. Nanocomposite material was done using SEM. As(V), Al, Ti, Zr, and Fe water samples were analysed by ICP-MS (inductively coupled plasma-mass spectrometry). Fluoride level was determined using the standard method – Ion-Selective Electrode method. Preliminary results indicate arsenic (V) removal was below the 10 ppb and fluoride less than 1.5 ppm as prescribed by WHO. The removal efficiency was after 60-70 minutes with recyclability of 11 cycles. The nanocomposite worked well in all pH ranges 6.5-8.5. A filter cartridge biopolymer metal oxide nanocomposite constituting of template aluminium homogenized in the aggregated network of chitosan was developed as an adsorbent for fluoride from the water with better adsorption limit.
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Introduction

Fluoride is beneficial to human health. However, levels exceeding 1.5 mg/L in drinking water is detrimental to human health. For example, occurrence of fluorosis. In addition, exposure to high concentration of fluoride for a long period of time may lead to kidney, brain and liver damage. Drinking water with elevated levels of fluoride exceeding 1.5 ppm is a serious health challenge globally. Fluoride has been associated with fluorosis and bone diseases.

Interventions such as reverse osmosis and adsorption have been made to reduce fluoride contamination in drinking water. However, some of these solutions are expensive for the poor and cannot be used in areas with no electrical power. With the emerging field of nanotechnology, nano-adsorbents have received considerable attention as an alternative solution to water purification. However, some of the nanomaterials are either powders or fine particles that render separation difficult due to blockage in columns, poor chemical and mechanical stability. This renders their application in point-of-use devices ineffective.

Therefore, the main aims of this study was to synthesize and investigate the potential of a nano-sized granulated biopolymer-mixed metal oxide nanocomposite in reduction of fluoride in drinking water and fabricate a point-of-use water filter device for house-hold and commercial scale. The specific objectives of this study were:

  • i.

    To synthesize and characterize chitosan – Aluminum, iron and titanium and zirconium nanocomposite.

  • ii.

    To evaluate the reduction efficiency of the nanocomposite for fluoride in drinking water.

  • iii.

    To investigate the influence of pH, competing ions, adsorbent dose, initial concentration contact time on the nanocomposite performance.

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Background

Occurrence of Fluoride

Fluoride is a compound derived from fluorine. Fluorine does not exist in elemental form but acquires the negative charge to form fluoride, which exists in many rocks and minerals (Jadhav and Jadhav, 2014). It is the 13th most abundant element in the earth’s crust and in the halogen family, it is the most electronegative and reactive (Waghmare et al, 2015). Fluoride in the earth’s crust exists in granite, limestone and sandstone rocks. Fluorspar (CaF2), sellaite (MgF2), fluoroapatite (Ca5(PO4)3F) and cryolite (Na3AlF6) are the main forms in which fluoride occurs (Tomar and Kumar, 2013). In cryolite form it is present in igneous rock whereas in fluorspar it is mainly found in sedimentary rocks (Mohapatra et al., 2009). Other forms in which fluoride can exist are topaz (Al2F2SiO4), amblygonite (Li(F, OH) AlPO4) and apophylite (KFCa4(Si8O20) 8H2O (Dongre et al.,2012). Table 1 below summarizes percentage fluorine in different fluoride bearing minerals.

Table 1.
Fluoride Bearing Minerals
MineralChemical Formula% Fluorine
SellaiteMgF261
VilliamiteNaF55
Fluorite (Fluorspar)CaF249
CryoliteNa3AlF645
Fluoroapatite[3Ca3(PO4)2Ca(F,Cl2)]34

Source: (Awasti et al., 2002)

Key Terms in this Chapter

Defluoridation: The process of removing fluoride from water.

Fluorosis: Permanent demineralization of bones and teeth.

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