Mitigation options - Fluoride treatment technologies - Revision history

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152.88.7.199: /* Membrane methods */

‎Membrane methods

← Older revision		Revision as of 08:40, 10 August 2026
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	==References==		==References==
	For references, please visit the page [[References - Geogenic Contamination Handbook]].		For references, please visit the page [[References - Geogenic Contamination Handbook]].
		+
		+	==Related articles on GAP Wiki==
		+	*[[Mitigation options]]
		+	*[[Mitigation options - Exploiting alternative water resources]]
		+	*[[Mitigation options - Arsenic treatment technologies]]

@@ Line 79: / Line 79: @@
 [[File:Figure_7.9.jpg|400px|thumb|right | Fig. 7.9 Calcium phosphate pellets that are used in combination with bone char in fluoride removal filters (“Nakuru Technique”)''(Terms of use: Cite original source from Handbook)'']]
-[[File:Figure_7.10.jpg|400px|thumb|right | Fig. 7.10 Design of a Nakuru Technique filter implemented in the Ethiopian Rift Valley by Eawag and Oromia Self-Help Organisation (OSHO)''(Terms of use: Cite original source from Handbook)'']][[File:Figure_7.11.jpg|400px|thumb|right | Fig. 7.11 Fluoride uptake as a function from field tests in Ethiopia and Kenya. Shaded areas show ranges for BC and CP obtained from laboratory tests done at NDC (Kenya) and Eawag (Switzerland) (Johnson et al., 2011)''(Terms of use: Cite original source from Handbook)'']]
+[[File:Figure_7.10.jpg|400px|thumb|right | Fig. 7.10 Design of a Nakuru Technique filter implemented in the Ethiopian Rift Valley by Eawag and Oromia Self-Help Organisation (OSHO)'' (Terms of use: Cite original source from Handbook)'']][[File:Figure_7.11.jpg|400px|thumb|right | Fig. 7.11 Fluoride uptake as a function from field tests in Ethiopia and Kenya. Shaded areas show ranges for BC and CP obtained from laboratory tests done at NDC (Kenya) and Eawag (Switzerland) (Johnson et al., 2011)'' (Terms of use: Cite original source from Handbook)'']]
 ===Contact precipitation (the Nakuru Technique)===
@@ Line 99: / Line 99: @@
 *'''Disadvantages:''' Regeneration of the filter medium is not possible; Fluoride removal efficiency is highly dependent on the flow rate, which makes its application in household filters difficult; Pellets used in the Nakuru Technique are not widely available commercially, as they are currently produced only by NDC in Kenya; Skill and experience are needed for pellet and bone char production; Kynofos21 (calcium phosphate raw material) might not be available locally and would have to be imported, or a local alternative found
-[[File:Figure_7.12.jpg|400px|thumb|right | Fig. 7.12 Left: Principle of Nalgonda technique (left): Alum and lime are added to the high fluoride water, the mixture is stirred and precipitates containing fluoride settle as sludge to the bottom of the solution Right: Community Nalgonda Unit installed by the Catholic Relief Service in the Ethiopian Rift Valley''(Terms of use: Cite original source from Handbook)'']]
+[[File:Figure_7.12.jpg|400px|thumb|right | Fig. 7.12 Left: Principle of Nalgonda technique (left): Alum and lime are added to the high fluoride water, the mixture is stirred and precipitates containing fluoride settle as sludge to the bottom of the solution Right: Community Nalgonda Unit installed by the Catholic Relief Service in the Ethiopian Rift Valley'' (Terms of use: Cite original source from Handbook)'']]
 ===Nalgonda technique===
 The removal of fluoride using alum as a coagulant was first proposed in the United States in the 1930s. It was later adapted by the National Environmental Engineering Research Institute (NEERI) in India in the 1970s and named the “Nalgonda Technique” (Nawlakhe et al., 1975, Fig. 7.12). It is an alum-based coagulation-flocculation method that requires alum (aluminium sulphate, Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>) and lime (calcium hydroxide, Ca(OH)<sub>2</sub>): Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> + 3Ca(OH)<sub>2</sub> -> 2Al(OH)<sub>3</sub> + 3Ca<sup>2</sup>+ + 3SO<sub>4</sub><sup>2-</sup>

@@ Line 15: / Line 15: @@
 A widely used method for the removal of fluoride is to pass the contaminated water through a filter bed that retains the fluoride. The binding of fluoride to the surface of granular filter materials is an adsorptive process. In developing countries, most filter materials that have a high affinity for fluoride are aluminium- or calcium-phosphate-based. On the following pages, we describe two commonly used materials: activated alumina and bone char.
-[[File:Figure_7.6.jpg|400px|thumb|right | Fig. 7.6 One type of activated alumina: Compalox (Albemarle®)]]
+[[File:Figure_7.6.jpg|400px|thumb|right | Fig. 7.6 One type of activated alumina: Compalox (Albemarle®) ''(Terms of use: Cite original source from Handbook)'']]
 ===Activated alumina===
 Activated alumina (AA) is a commercially available granular form of aluminium oxide (Al<sub>2</sub>O<sub>3</sub>) that can be used as a filter medium to remove a range of contaminants, including fluoride, from water (Fig. 7.6). In contact with water, the surface of the AA becomes hydrated and forms Al(OH)<sub>3</sub> with surface hydroxide groups (≡Al-OH). Negatively charged ions can replace the hydroxide (OH<sup>-</sup>) ion, as shown for fluoride:≡Al-OH + F<sup>-</sup> -> ≡Al-F + OH<sup>-</sup>
@@ Line 40: / Line 40: @@
 Bone char filters can be implemented at both the community and household scales (Fig. 7.7). Raw water is fed into columns or filters and is allowed to percolate through the system. Once the 1.5 mg/L fluoride threshold has been reached, the material needs to be regenerated or replaced.
-[[File:Figure_7.7.jpg|400px|thumb|right | Fig. 7.7 Community BC filter used in Kenya by the Nakuru Defluoridation Company (NDC)]]
+[[File:Figure_7.7.jpg|400px|thumb|right | Fig. 7.7 Community BC filter used in Kenya by the Nakuru Defluoridation Company (NDC)''(Terms of use: Cite original source from Handbook)'']]
 *'''Filter Material Production:''' The bone material needs to be largely free of flesh before it is charred. The charring is carried out in a kiln in a low-oxygen atmosphere at a temperature of 300 to 500°C for approximately 10 days, to produce bone char with the highest fluoride removal capacity with no organic remains (CDN, 2007). If the temperature is too high, the hydroxyapatite contained in bones changes to another mineral, and the resulting bone char has a significantly reduced uptake capacity. The desired product should be grey in colour. A soot-coloured product indicates the presence of organic material, and a white-coloured product indicates that the temperature was too high. After charring, the bones are crushed to size fractions between 0.4 and 4 mm, which are washed with solution a solution of sodium hydroxide (6 g/L, pH 13) to remove remaining organic substances. The bones are then rinsed with water and acidified with CO2 gas. In Ethiopia and Kenya, large kilns capable of charring several tonnes of bone per batch are used. In Thailand, small household furnaces have been tested in which householders can produce their own bone char (Smittakorn et al., 2010). Generally, in small-scale production, it may be harder to maintain quality control of the bone char produced than in larger, standardised processes. Note: Production requires skill and may take some time to perfect. Should a faulty batch containing residual organic substances that taint the water be used, it is probable that the trust of users will be irrevocably destroyed.
@@ Line 55: / Line 55: @@
 '''Synthetic “bone char”: HAP''' Bone char essentially consists of hydroxyapatite (“HAP”, Ca<sub>5</sub>(PO<sub>4</sub>)3OH). This material can also be produced synthetically using simple raw materials (lime and phosphoric acid). Laboratory studies have shown that synthetic HAP can have a clearly higher fluoride uptake capacity than BC. Synthetic HAP is already used for fluoride removal in Germany and Italy and was used in the past in the USA. Recently, the Nakuru Defluoridation Company in Kenya has also started producing HAP and is now testing the material in the field.
-[[File:Figure_7.8.jpg|400px|thumb|right|Fig. 7.8 An adsorption isotherm for fluoride]]
+[[File:Figure_7.8.jpg|400px|thumb|right|Fig. 7.8 An adsorption isotherm for fluoride''(Terms of use: Cite original source from Handbook)'']]
 '''Uptake capacities of filter materials:''' The uptake capacity of a filter material is important, because it provides information on how long a filter material will last. The maximum uptake capacity is attained when all available sites are occupied and occurs only at high dissolved arsenic or fluoride concentrations. At lower dissolved concentrations, the amount that is sorbed is proportional to the amount in solution:
 K<sub>d</sub> = C<sub>solid</sub>/C<sub>solution</sub>
@@ Line 78: / Line 78: @@
 Fluoride can be removed from solution by precipitation and coagulation processes, followed by the settling (or flotation) of the precipitates. This usually involves the addition of chemicals that act as precipitating agents. Established techniques involving precipitation or coagulation include the Nakuru technique, the Nalgonda technique and electrocoagulation.
-[[File:Figure_7.9.jpg|400px|thumb|right | Fig. 7.9 Calcium phosphate pellets that are used in combination with bone char in fluoride removal filters (“Nakuru Technique”)]]
+[[File:Figure_7.9.jpg|400px|thumb|right | Fig. 7.9 Calcium phosphate pellets that are used in combination with bone char in fluoride removal filters (“Nakuru Technique”)''(Terms of use: Cite original source from Handbook)'']]
-[[File:Figure_7.10.jpg|400px|thumb|right | Fig. 7.10 Design of a Nakuru Technique filter implemented in the Ethiopian Rift Valley by Eawag and Oromia Self-Help Organisation (OSHO)]][[File:Figure_7.11.jpg|400px|thumb|right | Fig. 7.11 Fluoride uptake as a function from field tests in Ethiopia and Kenya. Shaded areas show ranges for BC and CP obtained from laboratory tests done at NDC (Kenya) and Eawag (Switzerland) (Johnson et al., 2011)]]
+[[File:Figure_7.10.jpg|400px|thumb|right | Fig. 7.10 Design of a Nakuru Technique filter implemented in the Ethiopian Rift Valley by Eawag and Oromia Self-Help Organisation (OSHO)''(Terms of use: Cite original source from Handbook)'']][[File:Figure_7.11.jpg|400px|thumb|right | Fig. 7.11 Fluoride uptake as a function from field tests in Ethiopia and Kenya. Shaded areas show ranges for BC and CP obtained from laboratory tests done at NDC (Kenya) and Eawag (Switzerland) (Johnson et al., 2011)''(Terms of use: Cite original source from Handbook)'']]
 ===Contact precipitation (the Nakuru Technique)===
@@ Line 99: / Line 99: @@
 *'''Disadvantages:''' Regeneration of the filter medium is not possible; Fluoride removal efficiency is highly dependent on the flow rate, which makes its application in household filters difficult; Pellets used in the Nakuru Technique are not widely available commercially, as they are currently produced only by NDC in Kenya; Skill and experience are needed for pellet and bone char production; Kynofos21 (calcium phosphate raw material) might not be available locally and would have to be imported, or a local alternative found
-[[File:Figure_7.12.jpg|400px|thumb|right | Fig. 7.12 Left: Principle of Nalgonda technique (left): Alum and lime are added to the high fluoride water, the mixture is stirred and precipitates containing fluoride settle as sludge to the bottom of the solution Right: Community Nalgonda Unit installed by the Catholic Relief Service in the Ethiopian Rift Valley]]
+[[File:Figure_7.12.jpg|400px|thumb|right | Fig. 7.12 Left: Principle of Nalgonda technique (left): Alum and lime are added to the high fluoride water, the mixture is stirred and precipitates containing fluoride settle as sludge to the bottom of the solution Right: Community Nalgonda Unit installed by the Catholic Relief Service in the Ethiopian Rift Valley''(Terms of use: Cite original source from Handbook)'']]
 ===Nalgonda technique===
 The removal of fluoride using alum as a coagulant was first proposed in the United States in the 1930s. It was later adapted by the National Environmental Engineering Research Institute (NEERI) in India in the 1970s and named the “Nalgonda Technique” (Nawlakhe et al., 1975, Fig. 7.12). It is an alum-based coagulation-flocculation method that requires alum (aluminium sulphate, Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>) and lime (calcium hydroxide, Ca(OH)<sub>2</sub>): Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> + 3Ca(OH)<sub>2</sub> -> 2Al(OH)<sub>3</sub> + 3Ca<sup>2</sup>+ + 3SO<sub>4</sub><sup>2-</sup>
@@ Line 114: / Line 114: @@
 *'''Disadvantages:''' Insufficient fluoride removal efficiency when concentrations in raw water are high; The method is labour intensive and requires rigorous and time-consuming operation and maintenance; Some community filter units require power for the electrical stirrer; Electrical stirrers include movable parts, which are prone to mechanical failure; Perceived taste of the treated water may be affected by high sulphate concentrations (~ 600 mg/L); Large amounts of waste are produced that are often deposited onsite
-[[File:Figure_7.13.jpg|400px|thumb|right | Fig. 7.13 Schematic principle of electrocoagulation (left) and EC community plant operated by NEERI, India (right)]]
+[[File:Figure_7.13.jpg|400px|thumb|right | Fig. 7.13 Schematic principle of electrocoagulation (left) and EC community plant operated by NEERI, India (right)''(Terms of use: Cite original source from Handbook)'']]
 ===Electrocoagulation===
 The electrocoagulation (EC) method has been used to remove fluoride and other ions from industrial wastewaters for some time (e.g. Shen et al., 2003; Hu et al., 2008) and is now increasingly receiving attention as a suitable technology for fluoride removal from drinking water in developing countries. This technology lies at the intersection of three more fundamental technologies: electrochemistry, coagulation and precipitation. The method utilises metal (e.g. aluminium) plates that act as anode and cathode. When a potential is applied to the electrodes, a current flows and Al3+ is released at the anode and reacts with water at neutral pH to form precipitate of Al(OH)3, a compound which has a high affinity for fluoride (Fig. 7.13). The resulting Al(OH)<sub>3-</sub>F flocs settle at the bottom of the solution and can be removed as sludge.
@@ Line 129: / Line 129: @@
 ==Membrane methods==
 Membranes with fine pores can be used to separate contaminants from water physically. As the fluoride ion is very small, most membranes are not fine enough to retain it. Reverse osmosis is a technique utilising very fine membranes coupled with high pressures to remove fluoride from drinking water efficiently.
-[[File:Figure_7.14.jpg|400px|thumb|right | Fig. 7.14 Principle of reverse osmosis]]
+[[File:Figure_7.14.jpg|400px|thumb|right | Fig. 7.14 Principle of reverse osmosis''(Terms of use: Cite original source from Handbook)'']]
 ===Reverse osmosis===

← Older revision		Revision as of 08:40, 10 August 2026
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		+	''NOTE: Article from the Geogenic Contamination Handbook''
		+
		+
	A range of technologies are available for the removal of fluoride from drinking water. These can be divided into three categories based on the underlying fluoride-removal process:		A range of technologies are available for the removal of fluoride from drinking water. These can be divided into three categories based on the underlying fluoride-removal process:
	<br>		<br>

← Older revision		Revision as of 08:40, 10 August 2026
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	*'''Advantages''': Efficient fluoride removal; Reduction in salinity; Additional removal of chemical contaminants and pathogens		*'''Advantages''': Efficient fluoride removal; Reduction in salinity; Additional removal of chemical contaminants and pathogens
	*'''Disadvantages''': Complex and high maintenance process; Membrane fouling needing pre-treatment and chemical cleaning; High energy consumption; High water use; Cost-intensive		*'''Disadvantages''': Complex and high maintenance process; Membrane fouling needing pre-treatment and chemical cleaning; High energy consumption; High water use; Cost-intensive
		+
		+	==References==
		+	For references, please visit the page [[References - Geogenic Contamination Handbook]].

← Older revision	Revision as of 11:07, 10 May 2018
(No difference)

@@ Line 44: / Line 44: @@
 *'''Regeneration:''' Once the WHO drinking-water standard for fluoride (1.5 mg/L) or a national standard has been reached in the treated water, the filter material needs to be replaced or regenerated. Regeneration is typically done by passing a sodium hydroxide solution (0.25%–1%) through the BC bed, followed by rinsing with clean water. This results in caustic waste water rich in total dissolved solids and fluoride, which needs either to be neutralised or strongly diluted. The filter is then reactivated using CO<sub>2</sub> gas followed by flushing with water until the effluent has a pH of ~6. The fluoride removal capacity is lower after each regeneration cycle. The caustic waste can be treated with CaCl<sub>2</sub> or Ca(OH)<sub>2</sub> (lime) to produce a highly insoluble solid CaF<sub>2</sub> precipitate, which needs to be disposed of safely.
-*'''Costs:''' <br> Production of bone char is intensive in terms of infrastructure and labour. These costs and the cost of raw bones are the main contributors to the total costs. Charcoal for starting the charring process, electricity for crushing and sieving the charred bones, caustic soda for washing the bone char and bags for packing the final material are of comparatively minor importance.
+*'''Costs:''' Production of bone char is intensive in terms of infrastructure and labour. These costs and the cost of raw bones are the main contributors to the total costs. Charcoal for starting the charring process, electricity for crushing and sieving the charred bones, caustic soda for washing the bone char and bags for packing the final material are of comparatively minor importance.
 *'''Advantages:''' Bones as raw material are locally available at relatively low cost; Filtered water is neutral in taste and colour (if the BC has been correctly produced); Relatively short contact time required (around 30 minutes)
@@ Line 112: / Line 112: @@
 [[File:Figure_7.13.jpg|400px|thumb|right | Fig. 7.13 Schematic principle of electrocoagulation (left) and EC community plant operated by NEERI, India (right)]]
-===Electrocoagulation===<br>
+===Electrocoagulation===
 The electrocoagulation (EC) method has been used to remove fluoride and other ions from industrial wastewaters for some time (e.g. Shen et al., 2003; Hu et al., 2008) and is now increasingly receiving attention as a suitable technology for fluoride removal from drinking water in developing countries. This technology lies at the intersection of three more fundamental technologies: electrochemistry, coagulation and precipitation. The method utilises metal (e.g. aluminium) plates that act as anode and cathode. When a potential is applied to the electrodes, a current flows and Al3+ is released at the anode and reacts with water at neutral pH to form precipitate of Al(OH)3, a compound which has a high affinity for fluoride (Fig. 7.13). The resulting Al(OH)<sub>3-</sub>F flocs settle at the bottom of the solution and can be removed as sludge.
@@ Line 121: / Line 121: @@
 *'''Costs:''' Electrocoagulation uses simple and readily available materials (e.g. aluminium plating). An electricity source is needed (solar panels or a generator), which can result in high initial costs and, in the case of a generator, high operational costs as well.
-*'''Advantages:''' High fluoride removal efficiency (at pH 6–7); Simple system, no moving parts, + No hazardous chemicals used (unless pH adjustment with acid needed); Relatively small amounts of sludge generated
+*'''Advantages:''' High fluoride removal efficiency (at pH 6–7); Simple system, no moving parts, No hazardous chemicals used (unless pH adjustment with acid needed); Relatively small amounts of sludge generated
-*'''Advantages/Disadvantages:''' High SO<sub>4</sub><sup>2-</sup> concentrations in raw water can inhibit fluoride removal; Aluminium levels in treated water may exceed the level recommended by WHO level (200 μg/L); Energy source needed (e.g. solar energy); pH may need to be controlled; Requires relatively skilled staff
+*'''Disadvantages:''' High SO<sub>4</sub><sup>2-</sup> concentrations in raw water can inhibit fluoride removal; Aluminium levels in treated water may exceed the level recommended by WHO level (200 μg/L); Energy source needed (e.g. solar energy); pH may need to be controlled; Requires relatively skilled staff
 ==Membrane methods==

@@ Line 122: / Line 122: @@
 ==Membrane methods==
 Membranes with fine pores can be used to separate contaminants from water physically. As the fluoride ion is very small, most membranes are not fine enough to retain it. Reverse osmosis is a technique utilising very fine membranes coupled with high pressures to remove fluoride from drinking water efficiently.
+[[File:Figure_7.14.jpg|400px|thumb|right | Fig. 7.14 Principle of reverse osmosis]]
-'''Reverse osmosis'''
+'''Reverse osmosis'''<br>
 Reverse osmosis utilises a synthetic, semipermeable membrane, which allows the passage of water but not of ions or larger molecules. In principle, during the process of osmosis, water molecules move through the membrane along a concentration gradient from a high to a low dissolved salt concentration. The opposite effect is desired in the reverse osmosis process: pressure is applied on the membrane to overcome the osmotic pressure and to force water molecules from the concentrated solution to the fresh water side (Fig. 7.14). Reverse osmosis is widely applied for desalination and water purification purposes, including the removal of fluoride. More information on the principle of reverse osmosis and other membrane methods can be found in a range of documents, including Elimelech and Phillip (2011), Greenlee et al. (2009), Mulder (2000), Pontié et al. (2006) and Shannon et al. (2008).
@@ Line 132: / Line 132: @@
 Membrane fouling occurs when suspended particulate matter, colloids, bacteria and organic material are deposited on the surface of the membrane. To control fouling, a pre-filtration step or conventional pre-treatment (e.g. coagulation and disinfection) may be needed to remove the particulate, colloidal and dissolved organic matter causing the fouling. Chemical cleaning is used to restore the permeability of the fouled membranes. During reverse osmosis filtration, feed water is recirculated, and only a certain percentage (around 20–50%, depending on the system used) of the raw water ends up as treated water (permeate), the rest being waste. Reverse osmosis therefore has a high water demand and should not be used in areas of known water scarcity.
-Fluoride Removal Efficiency: Reverse osmosis can remove fluoride almost completely. Treated water can be deficient in minerals serving as essential micronutrients to humans and generally needs to undergo remineralisation before distribution.
+*'''Fluoride Removal Efficiency:''' Reverse osmosis can remove fluoride almost completely. Treated water can be deficient in minerals serving as essential micronutrients to humans and generally needs to undergo remineralisation before distribution.
-Costs: Reverse osmosis is a high-tech process needing skilled operators. Capital and operational costs are high. It is an energy-intensive technology, requiring the generation of high pressures. Electricity costs can therefore be substantial.
+*'''Costs:''' Reverse osmosis is a high-tech process needing skilled operators. Capital and operational costs are high. It is an energy-intensive technology, requiring the generation of high pressures. Electricity costs can therefore be substantial.
-'''Advantages'''
+*'''Advantages/Disadvantages''': + Efficient fluoride removal, + Reduction in salinity, + Additional removal of chemical contaminants and pathogens, - Complex and high maintenance process, - Membrane fouling needing pre-treatment and chemical cleaning, - High energy consumption, - High water use, - Cost-intensive