NF. RO has two modules which are often used such as hollow fibre and spiral
wound. RO membrane can remove 95% of fluoride from water. RO is an efficient
fluoride removal membrane process. RO membrane also separates salt ions, metal
ions, minerals, organic, inorganic and biomolecules. MF and UF separate particles
through membrane pores. MF membrane pore size (0.1–5μm) and UF (0.1–10μm)
diameter usually separates organic and biological cellular particle.
Ultrafiltration and microfiltration are similar to RO processes which are also
powered by pressure. Membrane material types, such as polysulfone, polyvinylidene
fluoride, polypropylene, polyacrylonitrile, cellulose acetate polymers and other
polymers, are commonly used. Many membrane materials have different properties
with regard to degree of hydrophobicity, antifouling, chemical and thermal resistance, pH and oxidant tolerance and surface charging. Hollow fibre membrane
module is used for water purification in both NF and MF. Both techniques are
used in water remediation and wastewater treatment (Pellegrin et al. 2013). Nanofiltration membranes are porous and consist of polyamide materials that filter both
organic and inorganic (divalent ions) and species (virus, bacteria), with a pore size of
0.001–0.01 μm. NF is widely used for softening hard water (Hilal et al. 2004).
Electrodialysis also uses the same procedure as RO, using electric current instead of
pressure to remove solute contaminants from water. Dialysis separates the solid
particles by passing the particles through a membrane instead of using a membrane
to retain the particles as water passes through it as in reverse osmosis and
nanofiltration. Ions are charged particles that move through selective membranes
(cation and anion) of the ions. Solute can be powered by either the Donnan effect or
an electric field related to it. Concentration differential factor is relevant acting as a
driving force for ion separation (Loeb 1921).
6.2
Source of Fluoride in Atmosphere
F contamination occurs in the environment due to natural activity and anthropogenic
activity shown in Fig. 6.1. F deposit in large amount in earth crust and F-rich rocks
and minerals are the main natural source of F contamination in water and soil. F-rich
minerals are fluorspar-CaF 2 (lime stones and sandstones), cryolite-Na 3 AlF 6
(granites) and fluorapatite-Ca 3 (PO 4 ) Ca(FCl 2 ), micas, sellaite MgF 2 , biotite K(Mg,
Fe) 3 AlSi 3 O 10 (OH, F) 2 , muscovite, topaz Al 2 SiO 4 (OH, F) 2 and amphiboles such as
tremolite and villiaumite NaF (Karunanithi et al. 2019). F after separation from rock
becomes mobile and enters into soil, vegetables, crops, and fruits. Other anthropogenic factors such as chemical fertilizer plants, smelting industries (metals such as
zinc, steel, etc.), glass, ceramic industries and power plants are responsible for
fluoride contamination in water, soil and air (Bhattacharya and Samal 2018). High
carbonate and bicarbonate containing water passed through these F-rich rocks; F
ions leached out and increase the F content in the groundwater (Saxena and Ahmed
2001).
6 Fluoride Remediation Using Membrane Processes
177
wound. RO membrane can remove 95% of fluoride from water. RO is an efficient
fluoride removal membrane process. RO membrane also separates salt ions, metal
ions, minerals, organic, inorganic and biomolecules. MF and UF separate particles
through membrane pores. MF membrane pore size (0.1–5μm) and UF (0.1–10μm)
diameter usually separates organic and biological cellular particle.
Ultrafiltration and microfiltration are similar to RO processes which are also
powered by pressure. Membrane material types, such as polysulfone, polyvinylidene
fluoride, polypropylene, polyacrylonitrile, cellulose acetate polymers and other
polymers, are commonly used. Many membrane materials have different properties
with regard to degree of hydrophobicity, antifouling, chemical and thermal resistance, pH and oxidant tolerance and surface charging. Hollow fibre membrane
module is used for water purification in both NF and MF. Both techniques are
used in water remediation and wastewater treatment (Pellegrin et al. 2013). Nanofiltration membranes are porous and consist of polyamide materials that filter both
organic and inorganic (divalent ions) and species (virus, bacteria), with a pore size of
0.001–0.01 μm. NF is widely used for softening hard water (Hilal et al. 2004).
Electrodialysis also uses the same procedure as RO, using electric current instead of
pressure to remove solute contaminants from water. Dialysis separates the solid
particles by passing the particles through a membrane instead of using a membrane
to retain the particles as water passes through it as in reverse osmosis and
nanofiltration. Ions are charged particles that move through selective membranes
(cation and anion) of the ions. Solute can be powered by either the Donnan effect or
an electric field related to it. Concentration differential factor is relevant acting as a
driving force for ion separation (Loeb 1921).
6.2
Source of Fluoride in Atmosphere
F contamination occurs in the environment due to natural activity and anthropogenic
activity shown in Fig. 6.1. F deposit in large amount in earth crust and F-rich rocks
and minerals are the main natural source of F contamination in water and soil. F-rich
minerals are fluorspar-CaF 2 (lime stones and sandstones), cryolite-Na 3 AlF 6
(granites) and fluorapatite-Ca 3 (PO 4 ) Ca(FCl 2 ), micas, sellaite MgF 2 , biotite K(Mg,
Fe) 3 AlSi 3 O 10 (OH, F) 2 , muscovite, topaz Al 2 SiO 4 (OH, F) 2 and amphiboles such as
tremolite and villiaumite NaF (Karunanithi et al. 2019). F after separation from rock
becomes mobile and enters into soil, vegetables, crops, and fruits. Other anthropogenic factors such as chemical fertilizer plants, smelting industries (metals such as
zinc, steel, etc.), glass, ceramic industries and power plants are responsible for
fluoride contamination in water, soil and air (Bhattacharya and Samal 2018). High
carbonate and bicarbonate containing water passed through these F-rich rocks; F
ions leached out and increase the F content in the groundwater (Saxena and Ahmed
2001).
6 Fluoride Remediation Using Membrane Processes
177