liquid into support layer (i.e. salt in liquid state immobilized into metal porous layer
or ceramic supports). Gold nickel, stable zirconia, palladium and its alloys are
examples of thick membranes. Non-porous membrane separation efficiency depends
on the type of material, chemical and physical strength between pollutant and
membrane and nature of the pollutant to be separated. Non-porous membranes
exhibited high water purification efficiency and remove most contaminants
(1–10 nm) from wastewater, such as metal ion, acidic and basic salts, organic
particles and microbes (bacteria, virus). The general types of inorganic membranes
are liquid and fluidic membrane, glass, zeolite, iron, synthetic (inorganic)
membranes, silica (SiO 2 ), alumina (Al 2 O 3 ), titanium (TiO 2 ) and zirconia (ZrO 2 ).
Carbon-based membranes (graphene, carbon nanotubes) are used mainly for water
treatment. Various methods are available for the synthesis of inorganic membranes,
e.g. chemical vapour deposition (CVD), sol-gel method, slip casting, pyrolysis
technique, etc. (Fard et al. 2018). Ceramic membrane: The most commonly used
materials for membrane synthesis are aluminium (Al 2 O 3 ), titanium (TiO 2 ), zirconia
(ZrO 2 ), glass (SiO 2 ), silicon carbide (SiC) or a composite of these metal oxides.
Other materials include suitable non-oxide (carbide, nitrides, boride), oxides and
non-oxide composites. Ceramic membranes have different porosity layers and
asymmetrical structure. Multichannel monolith ceramic, flat and tubular membranes
are commercially available in markets. Compared to other membrane structures
tubular membranes have a high surface ratio. Tabular ceramic membrane synthesis
includes three primary phases: (a) paste or suspension preparation from ceramic
powder, (b) paste or suspension converted into flat or tubular geometry and
(c) calcination and sintering heat treatment (Li 2007).
6.4.2.3 Hybrid Membrane
Inorganic-organic hybrid membranes are typically turned into a polymeric matrix
structure by adding inorganic materials (metals, metal oxide or carbon-based
materials) shown in Table 6.5. Hybrid membranes have fewer drawbacks as compared to polymeric membrane. Incorporate inorganic material into polymeric matrix
to form multipurpose use and improve antifouling, water permeability, mechanical
strength and rejection rate. Membrane surface structure and pore structure are
modified by inorganic material (CNT). Several methods are available for hybrid
membrane synthesis, such as blending (properly combining nanomaterial and polymer matrix), interfacial polymerization, surface coating with nanocomposite material, layer by layer deposition and surface grafting of nanoparticles (Wang et al.
2012).
6.5
Membrane-Based Techniques for Fluoride Removal
Most utilizing membrane-based techniques for fluoride removal are reverse osmosis
(RO), nanofiltration (NF) and electrodialysis (ED).
The RO membrane cycle reverses the normal osmosis arising from the hydraulic
pressure applied to the high concentration side of the solution. Through
6 Fluoride Remediation Using Membrane Processes
187
or ceramic supports). Gold nickel, stable zirconia, palladium and its alloys are
examples of thick membranes. Non-porous membrane separation efficiency depends
on the type of material, chemical and physical strength between pollutant and
membrane and nature of the pollutant to be separated. Non-porous membranes
exhibited high water purification efficiency and remove most contaminants
(1–10 nm) from wastewater, such as metal ion, acidic and basic salts, organic
particles and microbes (bacteria, virus). The general types of inorganic membranes
are liquid and fluidic membrane, glass, zeolite, iron, synthetic (inorganic)
membranes, silica (SiO 2 ), alumina (Al 2 O 3 ), titanium (TiO 2 ) and zirconia (ZrO 2 ).
Carbon-based membranes (graphene, carbon nanotubes) are used mainly for water
treatment. Various methods are available for the synthesis of inorganic membranes,
e.g. chemical vapour deposition (CVD), sol-gel method, slip casting, pyrolysis
technique, etc. (Fard et al. 2018). Ceramic membrane: The most commonly used
materials for membrane synthesis are aluminium (Al 2 O 3 ), titanium (TiO 2 ), zirconia
(ZrO 2 ), glass (SiO 2 ), silicon carbide (SiC) or a composite of these metal oxides.
Other materials include suitable non-oxide (carbide, nitrides, boride), oxides and
non-oxide composites. Ceramic membranes have different porosity layers and
asymmetrical structure. Multichannel monolith ceramic, flat and tubular membranes
are commercially available in markets. Compared to other membrane structures
tubular membranes have a high surface ratio. Tabular ceramic membrane synthesis
includes three primary phases: (a) paste or suspension preparation from ceramic
powder, (b) paste or suspension converted into flat or tubular geometry and
(c) calcination and sintering heat treatment (Li 2007).
6.4.2.3 Hybrid Membrane
Inorganic-organic hybrid membranes are typically turned into a polymeric matrix
structure by adding inorganic materials (metals, metal oxide or carbon-based
materials) shown in Table 6.5. Hybrid membranes have fewer drawbacks as compared to polymeric membrane. Incorporate inorganic material into polymeric matrix
to form multipurpose use and improve antifouling, water permeability, mechanical
strength and rejection rate. Membrane surface structure and pore structure are
modified by inorganic material (CNT). Several methods are available for hybrid
membrane synthesis, such as blending (properly combining nanomaterial and polymer matrix), interfacial polymerization, surface coating with nanocomposite material, layer by layer deposition and surface grafting of nanoparticles (Wang et al.
2012).
6.5
Membrane-Based Techniques for Fluoride Removal
Most utilizing membrane-based techniques for fluoride removal are reverse osmosis
(RO), nanofiltration (NF) and electrodialysis (ED).
The RO membrane cycle reverses the normal osmosis arising from the hydraulic
pressure applied to the high concentration side of the solution. Through
6 Fluoride Remediation Using Membrane Processes
187