Synthesis Arsenic Fluoride Lead
BLARD
ECOLE NATIONALE DU GENIE RURAL DES EAUX ET DES FORETS
ENGREF
TECHNICAL SYNTHESIS
MITIGATION TECHNIQUES FOR DRINKING WATER
CONTAMINATED BY ARSENIC, FLUORIDE OR LEAD
BLARD Sébastien
E-mail:
blard@engref.fr
December 2005
Office International de l’Eau
15 rue Edouard Chamberland
87 650 LIMOGES
Tél. (33) 05 55 11 47 47
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ENGREF Centre de Montpellier
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ORIGINAL TITLE
LES TECHNIQUES DE TRAITEMENT DES EAUX CHARGEES EN ARSENIC, FLUOR ET PLOMB
SUMMARY IN FRENCH
Le renforcement des normes de qualité de l’eau destinée à la consommation humaine entraîne le
développement de nouveaux procédés. L’arsenic, le fluor et plus rarement le plomb peuvent être
naturellement en concentration supérieure à la norme. Pour chacun de ces trois éléments, les
procédés de traitements seront détaillés en insistant sur les avantages, les inconvénients, les
coûts et les dimensionnements. Les procédés peuvent être classiques, membranaires,
biologiques ou encore basés sur l’échange ionique ou l’adsorption sélective. Des exemples de
pilotes et d’usines seront mentionnés.
FRENCH KEY WORDS
ARSENIC, FLUOR, PLOMB, EAU POTABLE, TRAITEMENT
SUMMARY
Local and international guidelines have been reinforced for drinking water quality. Therefore, new
mitigation technologies are under development. Arsenic, fluoride and more rarely lead can be
found naturally in underground water in levels higher than the new guidelines. For each of these
compounds mitigation techniques are presented, focusing on the advantages, disadvantages,
costs and capacity. Methods presented can be basic, membranes, biological or based on ion
exchange or selective adsorption. Examples of pilots and water treatment plants are provided.
KEY WORDS
ARSENIC, FLUORIDE, LEAD, DRINKING WATER, MITIGATION
TABLE OF CONTENTS
NATURAL ORIGIN, EFFECTS ON HEALTH AND AFFECTED ZONES ....................................... 3
o ARSENIC ............................................................................................................................... 3
o FLUORIDE ............................................................................................................................. 4
o LEAD ..................................................................................................................................... 4
MITIGATION TECHNIQUES FOR ARSENIC................................................................................ 5
o BASIC TREATMENTS ........................................................................................................... 5
o SELECTIVE ADSORPTION ................................................................................................... 6
o MEMBRANE TECHNOLOGIES ............................................................................................. 9
o BIOLOGICAL TECHNIQUES ................................................................................................10
MITIGATION TECHNIQUES FOR FLUORIDE ............................................................................11
o PRECIPITATION...................................................................................................................11
o ADSORPTION ......................................................................................................................11
o ION EXCHANGE...................................................................................................................11
o MEMBRANE TECHNIQUES .................................................................................................11
o OTHER TECHNIQUES .........................................................................................................12
MITIGATION TECHNIQUES FOR LEAD .....................................................................................12
MITIGATION TECHNIQUES FOR ARSENIC, FLUORIDE AND LEAD ........................................13
o COMPATIBLE TREATMENTS ..............................................................................................13
o TABLE OF MITIGATION TECHNIQUES FOR ARSENIC ......................................................14
o TABLE OF MITIGATION TECHNIQUES FOR FLUORIDE ....................................................16
o EXAMPLES...........................................................................................................................16
REFERENCES ............................................................................................................................17
APPENDICIES .............................................................................................................................21
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INTRODUCTION
Arsenic, fluoride and lead are rarely naturally present at the same time. In the Nièvre, the water
table of the Bazois area is affected by pollution from these three elements. This water table
regroups 10 administrative entities, 80 local authorities and six CAPTAGES grouped two by two.
The three resulting water resources provide water to 3000 to 5000 subscribers each ( Kayser,
2005 ). Evolution in standards for arsenic, lead and fluoride implies research and development of
mitigation techniques available for small structures. After an overview of the origins of the
contamination and affected zones, mitigation techniques found in the literature will be presented
for each of these compounds, taken separately then together.
NATURAL ORIGIN, EFFECTS ON HEALTH AND AFFECTED ZONES
o ARSENIC
Origin of high levels of arsenic and predominant forms
The presence of arsenic in groundwater is linked to geological and geochemical characteristics
( Raihane, 1999 ). Arsenic is present in eruptive and metamorphic rocks. This compound is then
spread during changes in rock structures ( AFSSA, 2004 ). It is the twentieth most abundant
compound in the Earth’s crust and is often associated with sulphurized minerals : arsenopyrite
(FeAsS), realgar (As2S2) and orpinet (As2S3) ( Pedron, 2004 ). Arsenic has a strong affinity for iron
hydroxides. High levels of arsenic can be associated to the dissolution of iron hydroxides
containing some arsenic ( Welch, et al., 2000 ). 90 % of arsenic is inorganic ( Raihane, 1999 ).
The two main forms are arsenate, As (V) with the formula H2AsO4- or HAsO3 and arsenite, As
(III), with the formula H3AsO3. The neutral form of arsenic, As (III), is more toxic and more mobile.
Effects on health of high levels of arsenic and legislation
Effects due to arsenic are many and varied: skin troubles, gangrene, cardiovascular or pulmonary
diseases, high blood pressure and cancers. High concentrations can induce arsenicose ( MAGC
Technologies Limited). The French standard for arsenic in drinking water is 10 micrograms
per liter (µg/l) ( Décret n°2001-1220, 2001 ). The same standard is enforced by the United States
Environmental Protection Agency (US EPA) and the World Health Organization ( WHO, 2004 ). In
France, water containing more than 100 µg/l of arsenic cannot be treated to reach the
standard. ( Décret n°2001-1220, 2001 ). Between 10 and 13 µg/l, it is possible to bypass the
standard but only for a short time and with restrictions of usage ( Direction Générale de la Santé,
2005 ).
Affected zones by high level of arsenic
In France, the areas concerned have special geological characteristics. These zones are cold
“base” like the Hautes-Pyrénées, the Vosges, the Allier, the west part of the Morvan or the Puy de
Dôme ( Pedron, 2004 ). In this latter department, several levels of arsenic above the standard
have been monitored: 17 to 20 µg/l at Goulet de Volvic, 50 µg/l at Charbonnière les Varennes and
20 to 40 µg/l at Cunlhat. In the Vosges, the town of Ambacourt considered a pilot scale
experiment using biological removal of iron that could also remove arsenic ( Pedron, 2004 ). In the
Savoie department, contaminated zones are linked with the geological structure of the ground
beneath ( Cadic, 2002 ). The level of arsenic reaches 32 µg/l for the intake Dienne (town of
Châtillon-en-Bazois in the Nièvre department).
France is not the only European country with high levels of arsenic. The United Kingdom ( MAGC
Technologies Limited), Italy and Greece ( Robin, 2005 ) are also affected, especially in
mountainous areas. In Hungary and Romania, arsenicosis cases have been reported ( WHO,
2004 ).
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In Bangladesh and West Bengal, 35 million inhabitants are exposed to concentrations above 50
µg/l. 20 to 25 million more live in areas with more than 10 µg/l arsenic in their drinking water. In
these countries, 90 percent of drinking water comes from wells and half are contaminated by
arsenic ( Raihane, 1999 ). Other countries facing high concentration of arsenic are Argentina,
Mongolia, China, Thailand and the state of California in the United States ( MAGC Technologies
Limited).
o FLUORIDE
Origin of high levels of fluoride and predominant forms
The natural occurrence of fluoride comes from the dissolution of some rocks into water. Important
factors are geology, contact time with fluorinated minerals, the chemical composition of
underground water or climate ( British Geological Survey and WaterAid, 2002 ). Fluoride is not
very abundant in the Earth’s crust (0.028 % of its weight) but it is widely spread. Fluoride is
present in Calcium Fluoride, CaF2, in fluorspar (also called spathfluor), in cryolite and fluorapatite
Ca5[F Cl (PO4)3] (Tierra Toxic, Donald O’ Leary 2000).
Effects on health of fluoride and legislation
If the level of fluoride in tap water is below 0.5 mg/l, a nutritional contribution is required to prevent
dental decay (20, 000 persons are on prescription in the Nièvre department). Between 0.5 and 1.5
mg/l, good dental health favoured. From 1.5 to 4 mg/l, there is a risk of dental fluorosis. Between
4 and 10 mg/l, fluorosis affects teeth and bones. Above 10 mg/l, an advanced stage called
crippling fluorosis is reached ( British Geological Survey and WaterAid, 2002 ). The World Health
Organization (WHO) defines two standards for fluoride. In areas where the weather is rather
warm, fluoride in drinking water must be below 1 mg/l. In colder areas, the limit changes to 1.2
mg/l. The difference is explained by a higher consumption of water in warmer zones, due to sweat
and respiration. At concentrations above 1.5 mg/l, adverse effects of fluoride are stronger than the
positive effect on dental health. The standard for fluoride in drinking water is fixed to 1.5 mg/l
( Décret n°2001-1220, 2001, WHO, 2004 ). Between 1.5 and 2 mg/l, it may be possible to bypass
the standard but only for a short time and with restriction of usage ( Direction Générale de la
Santé, 2005 ).
Zones affected by high levels of fluoride
At a local level, there are concentrations of fluoride above the standard in England, France and
Italy. Cases of fluorosis are reported in other European countries such as Spain, Germany and
Norway ( WHO, 2004 ). In the United States, the pollution is at a larger scale. In India, 66 million
people are exposed to high fluoride levels, including 7 million children. There is no treatment
available against fluorosis except drinking water with less fluoride ( MAGC Technologies Limited).
The highest levels of fluoride are monitored in water with very low levels of calcium ( AFSSA,
2004, Mazet, 2002 ) as in East Africa, where alkaline granite poor in calcium is present ( British
Geological Survey and WaterAid, 2002 ).
o LEAD
Contamination of drinking water is generally linked to the dissolution of lead pipes by corrosive
water. The natural occurrence of lead in water is rare ( Robin, 2005 ). For instance, at Monceauxle-Comte in the Nièvre department, high levels of lead are reported (26 µg/l on average). The
French standard is 25 µg/l since December 25th 2003 and the next goal is 10 µg/l by
December, 26th 2013. Ground water containing more than 50 µg/l cannot be treated to become
drinking water. If the water is only to be disinfected, the highest concentration of lead allowed is
10 µg/l.
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Lead is usually present at unimportant levels in surface or ground water. Lead is in fact trapped in
sediment or rock. In France, between 1999 and 2002, 1.5 % of water resources tested positive to
a level of lead higher than 10 µg/L (0,4 % above 25 µg/L) ( Direction Générale de la Santé,
2003 ). There is no way to bypass the standard for a natural contamination ( Direction
Générale de la Santé, 2005 ).
MITIGATION TECHNIQUES FOR ARSENIC
There are at least fifty techniques to remove arsenic from water ( Clayton, 2005 ). In France,
authorized treatments are listed in an official document : set out in a circular of 28th March 2000
( Direction Générale de la Santé, 2000 ). To be up to date, the GEH® process from Degrémont
must be added to the list. The efficiency of this treatment depends on the pH. The list is not
closed because all treatments also based on ferric oxyhdroxide could listed ( Robin, 2005 ).
Several theses and syntheses have summarised the available treatments to remove arsenic from
drinking water ( CIRSEE, 2002, Dictor, et al., 2004, Lenoble, 2003, Simeonova, 2004 ).
If no treatment is applied, options are to search for new resources or to mixi with water resources
of better quality ( US EPA, 2002 ).
Several aspects of these processes have been studied: description, costs, advantages and
disadvantages, by-products, efficiencies and examples. The main results are shown in charts at
the end of this synthesis. The processes were divided into 4 categories: basic treatments,
selective adsorption or ion exchange, membrane techniques and biological processes. Oxidation
and adsorption are often preferred in rural areas (flow rate below 10 m3/h) ( Lenoble, 2003 ).
Phosphates have a similar configuration to arsenic and could compete with arsenic removal
( Meng, et al., 2001 ). Sulphates and carbonates have little effect on arsenic removal despite their
close structure ( Laperche, et al., 2003 )
o BASIC TREATMENTS
These treatments are sometimes already implemented in a treatment plant for other quality
problems. This is the case for instance for iron or manganese removal treatments.
Oxidation
Oxidation transforms As (III) into a less soluble form As (V). Several oxidants can be used :
hydrogen peroxide (H2O2), sodium hypochlorite (NaOCl) and potassium permanganate (KMnO4)
( Meng, et al., 2001 ). Other reagents are possible such as ferric chloride (FeCl3) or manganese
dioxide (MnO2) ( Lenoble, 2003 ). Potassium permanganate and ferric chloride tuned out to be
most to use.
H2O2 NaOCl FeCl3 KMnO4
Stability
No
No
Yes
Yes
Risk
No
Yes
No
No
Increase of waste
No
No
Yes
Yes
Cost
High
low
low
low
Reagents capable of arsenite As (III) oxidation ( Lenoble, 2003 )
Hydrogen peroxide requires a large excess. Sodium hypochlorite and ferric chloride are studied in
Lenoble’s thesis because further experiments were required. Potassium permanganate is a good
choice because a quantity smaller than the stoechiometry is actually required. Chlorine (Cl2) can
also be used ( US EPA, 2002 ).
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Precipitation / Co-precipitation ( Meng, et al., 2001 )
 Lime softening
Direct precipitation of As (V) is possible in presence of calcium. The conditions required are the
use of lime at a pH of 10.5 ( Dictor, et al., 2004 ). Decarbonatation is effective to remove arsenic
with lime or sodium hydroxide. A co-precipation is possible between As (V) and calcium carbonate
CaCO3. Arsenic removal is very effective if magnesium is present ( AFSSA, 2004 ) and barium
could also play a role. This process requires skilled workers and sludge is produced. This
technique is not relevant if the water is little mineralized or poor in calcium. On the other hand, it is
an interesting choice if a softening process is already implemented.
 Use of ferric or aluminium salts
Arsenic interferes with ferric cations (III) to produce a ferric arsenate. After this reaction, a coprecipitation takes place between ferric hydroxide and ferric arsenate. Only arsenate As (V) is
effectively removed, an oxidation is therefore required to transform As (III) into As (V). Results are
better in acid conditions and pH must be below 7.5 ( AFSSA, 2004 ). Efficiency rates are better
with ferric salts than aluminium salts (removal rate of 90 to 98 % versus 80 to 85 %). Reagents
used are ferric chloride, aluminium chloride (PAC), ferric sulphate or aluminium sulphate ( Dictor,
et al., 2004 ). Lime is sometimes used to control the pH. This process required skilled workers
and produces sludge. Removal rate is proportional to the amount of iron added. High manganese
concentrations ([Mn] > 1500 mg/l) and a pH between 5 and 6 can increase the efficiency of the
process ( Dictor, et al., 2004 ). Coagulation with ferric chloride FeCl3 requires a concentration of
reagents between 1 and 3 g/m3.
Final concentration As
6 µg/l
< 4 µg/l
Concentration Fe needed
1 mg/l
2 mg/l
Concentration PAC needed
15 mg/l
25 mg/l
Example of reagents concentration to remove arsenic ( US EPA, 2002 )
Initial concentration of As 14.3 µg/l
Ferric chloride is far more effective than aluminium chloride at low concentrations. A mix of
aluminium and iron salts is possible, it is the case for instance in Billings Water Treatment Plant in
Montana in the United States. 2 g/m3 ferric chloride and aluminium chloride are combined to
reduce arsenic levels from 15 µg/l to 2 µg/l. In France, the water treatment plant in Baudricourt in
the Vosges department uses ferric chloride. This plant built in 1996 by OTV is designed for 100
m3/h (20h/24h) ( Hydroland, 2005 ). After an oxidation by chlorine, 10 to 15 g/m3 FeCl3 is added to
the water containing 50 to 100 µg/l arsenic. Sludge produced is collected during the washing of
the two sand filters. They are then thickened and dried. Sludge production is between 15 and 20
kg/day. After treatment, the arsenic level is between 2 and 4 µg/l.
o SELECTIVE ADSORPTION
Selective adsorption can take place on several materials : activated clay, metallic oxides (hydrous
iron, Al, Ti, Si), hydroxides (iron, aluminium or manganese) or cellulose based compounds
( Simeonova, 2004 ). The most commonly used products are oxides, iron oxide or manganese
coated sands, minerals containing iron, aluminium or manganese (bauxite, feldspar…) and clays
( Simeonova, 2004 ). Non-renewable systems can be used on low flow rates and levels of arsenic
below 25 µg/l. The disadvantage is the production of high quantities of contaminated solids that
have to be disposed of. To reduce volumes in landfills (class I in France), materials with the best
efficiency are selected (Volume of treated water per volume of material V/V).
Activated Alumina Al2O3 ( Sarvinder, et al., 2004 )
Only As (V) is removed and an oxidation is needed. Fluorides compete for this process, as well as
sulphates, chlorides and humic acids ( Welté and Montiel, 2004 ). This process changes ionic
equilibrium and produces liquid waste during regeneration and sludge.
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Several activated alumina units can be installed in series. Operating costs are between 0.1 to 0.3
€ per m3 after an investment of 5000 € per m3/h. Modifications of alumina can increase efficiency.
There exists Iron modified or high porosity alumina ( US EPA, 2002 ).
Example 1: Vieux Ferrette in the Haut Rhin department
15 m3/h, 25000 m3/year, 10 to 20 µg/l As
In 2001, the SAUR company proposed a price of 32000 € without taxes for the treatment unit
which represents 0.10 €/m3. Alumina is renewed every year and a half for an average cost of
1200 €/year. Disposal of activated alumina costs 1400 €/year. Therefore, reagent costs are
around 0.10 €/m3. Investment and operating costs included, the bill is around 0.20 €/m3.
Example 2: A pilot unit has been designed near Boston (MA, USA) ( US EPA, 2002 )
For 60 inhabitants, arsenic levels were reduced from 150 - 1100 µg/l to 5 µg/l.
Example 3 : In Bangladesh, Alcan enhanced activated alumina is the most used material ( NGO
Forum for Drinking Water Supply & Sanitation, 2002 ).
Collective unit
Individual unit
Flow rate
> 300 l/h
< 100 l/h
Price
$170
$34
Lifetime
20 years
Material costs
$220
$14
Capacity of treatment
80 m3
11 m3
Manufacturer
( MAGC Technologies Limited)
( NGO Forum for Drinking Water Supply & Sanitation, 2002 )
GFH ( Moles, et al., 2004, Thirunavukkarasu, et al., 2003 )
Ferric oxyhydroxides have a strong affinity for arsenic. This compound can be found under
several names: GEH® or GFH® (Granular Ferric Hydroxide). This process is the most used coprecipitation technique ( Pedron, 2004 ). At a pH below 8, As (III) and As (V) are both removed,
As (III) twice less than As (V).
This technique does not require skilled workers and can be with or without renewal of the media.
The adsorption potential is huge, it can reach 100 000 volumes of treated water per volume of
filtration media. The life cycle of this compound can be longer than one year due to this high
capacity. Backwashing with water is required every two weeks ( Moles, et al., 2004 ).
Backwashing prevents filling of the filter but arsenic is still adsorbed. Media is disposed of in class
I landfills.
Examples:
GEH®, developed by ONDEO DEGREMONT ( AFSSA, 2000 ) is the only approved process in
France ( Direction Générale de la Santé, 2000 ). La Lyonnaise des Eaux (Suez Environnement) is
designing its own granules ( Kayser, 2005 ).
In developing countries, a tea bag of bottom ash coated by ferric hydroxide car reduce arsenic
levels from 2400 µg/l to 10 µg/l ( Clayton, 2005 ).
Hydrous ferric oxides (HFO) can be used on goethite to remove arsenic for instance ( Lenoble,
2003 ). Best results are reported with HFO in acid conditions than with ferric oxides such as
Fe2O3. It is also possible to use ferric hydroxide coated polymers. This combination is more
profitable because it creates less sludge ( Katsoyiannis and Zouboulis, 2002 ). With polyHIPE
used as polymers, it is possible to get below 10µg/l.
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Manganese oxide MnO2 ( Driehaus, et al., 1995 )
At a pH below 8, both As (III) and As (V) are removed. There is no use for an oxidation
beforehand. This process requires skilled workers. The media can be ore or coated sand.
Filtration on manganese oxide coated sand is used for instance to remove arsenic before bottling
water: « Clairvic » Volvic ( AFSSA, 2000 ), « Bonne source » et « Source des Frères » Vittel
( AFSSA, 2000 ). Danone customer service confirmed the use of this process for Vittel mineral
bottled water.
Ferruginous manganese ore also works for arsenic removal ( Chakravarty, et al., 2002 ). This
compound has the advantage of its low price: $50 – 56 per ton of ore.
Innovative techniques are under development ( Lenoble, 2003 ) such as manganese oxide coated
polystyrene. In one-step, there is oxidation and adsorption. Another kind of media, anionic resins
could remove As (V) from water. At most, 53 mg As (III) (0.7 mmol) and 22 mg As (V) (0.3 mmol)
were trapped per gram of resin ( Lenoble, 2003 ). The precipitate formed between As (V) and Mn
(II) is Mn3(AsO4)2. There is a strong capacity of adsorption and no competitor has been
discovered yet. These compounds have little possibility of regeneration.
Ferric oxide Fe2O3 ( Roberts, et al., 2004 )
Ferric ores are sometimes used to remove arsenic. This process is easy to operate and not costly
but it is sometimes not sufficiently effective to get below 10 µg/l ( Zhang, et al., 2004 ). Several
media can be used as support for Fe2O3:
 Goethite, haematite or sand ( Welté and Montiel, 2004 )
 Anthracite or granular activated carbon (GAC)
Yields for arsenic removal are ( Simeonova, 2004 ) :
 60 % for a combination of anthracite and Fe2O3
 50 % for Fe2O3 coated sand
 Granular activated carbon gives better yields with ferrous oxides Fe (II) than ferric oxides
Fe (III)
Other ores and oxides
Two compounds, kutnahorite and chabazite, have been studied for their ability to remove arsenic
but also to create a suitable media for biological removal ( Lievremont, et al., 2003 ).
Kutnahorite is a manganese and calcium carbonate (CaMn(CO3)2) and chabazite is a porous
zeolite aluminosilicate (CaAl2Si4O12, 6H20). This process has been used only on a bench ( Dictor,
et al., 2004 ).
Other media and innovative compounds
 Iron sulphide
This reaction takes place in anoxic conditions ( Simeonova, 2004 ). Arsenic can also be adsorbed
on triolite (FeS) or pyrite (FeS2) ( Bostick and Fendorf, 2003 ) and arsenopyrite is formed
(FeAsS). Triolite (FeS) gives better yields than alumina (Al2O3). The United States Environmental
Protection Agency also considers sulphur-modified iron (SMI) as a possible innovation ( US EPA,
2002 ).
 Activated carbon
Activated carbon can be found in two forms: granular and solid block. This media can remove
arsenic if it is especially designed. It can also be used in combination with ferric oxides.
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 Activated clays ( Lenoble, 2003 )
Clays are among the most used media ( Simeonova, 2004 ) : kaolinite, bentonite, bijoypur clay,
zeolite, khabazite… Clays are chemically modified with iron, titanium or aluminium. Clay layers
are pushed aside by insertion of metal pillars. The number of sites for adsorption is increased by
reaction of a chemical on cleansed bentonite (montmorillonitic fraction). Oxyhydroxides give better
results than clays, however, iron activated clays are the only media which can be regenerated at
100 %. Yields are higher in acid conditions.
 Organic materials containing cellulose ( Simeonova, 2004 )
Sawdust or paper pulp can be used to remove arsenic. Chitin structure is close to cellulose one.
Chitin and chitosan are polymers formed by saccharides, containing respectively more than 5000
units of glucosoamine or acetylglucosoamine ( Dambies, et al., 2000, Dambies, et al., 2002 ). The
authors tested arsenic removal by passage on a chitosan bed soaked with molybdates ( Dictor, et
al., 2004 ). With a pH between 2 and 3, arsenic adsorption is maximum and molybdates leakage
minimum.
Permeable barrier
It is an in situ passive treatment ( Dictor, et al., 2004 ). Permeable barriers are not suitable for
every application ( Dictor, et al., 2004 ) : pollution is rarely due to only one compound and other
pollutants can be released at high concentrations. No maintenance is possible and mechanical,
geochemical or biological filling in of cracks are likely.
Iron or aluminium oxyhydroxides can also remove arsenic in oxidizing conditions. Zero-valent iron
also allows an oxido-reduction and adsorption of arsenic and can remove both As (III) and As (V)
( Dictor, et al., 2004 ). Tommy Ngai, working at the MIT, designed a rustic remediation solution for
developing countries. Contaminated water is transferred in a plastic bucket containing sand,
crushed brick, small stones and nails ( Clayton, 2005 ). In this process, iron fixes arsenic for a
cost of $16 per treatment unit. One disadvantage of this technique is the likely leakage of ferrous
iron into the treated water ( Simeonova, 2004 ). This is a one-step process.
Ion exchange
This technique is sometimes listed among membrane techniques. Ion exchange works with anion,
a preliminary oxidation of As (III) into As (V) is required. Holding of anions is difficult if levels are
already very low. There are moreover difficulties in dealing with solutions containing arsenic. This
process is convenient for large scale systems ( Simeonova, 2004 ). Sulphate specific resins
remove arsenic also because of the similar structure between the two chemicals. Magnetic Ion
Exchange (MIEX) is a possible enhancement ( US EPA, 2002 ).
o MEMBRANE TECHNOLOGIES
These techniques are effective but expensive ( Lenoble, 2003, Simeonova, 2004, Zhang, et al.,
2004 ). Arsenic is not easily removed by other technologies, this explains why this technology is
sometimes selected ( Simeonova, 2004 ). Membranes are usually used as a last stage removal of
arsenic. It is possible to get as low as 2 ng/l arsenic ( Dictor, et al., 2004 ). The main disadvantage
of membrane technologies is cost. The ratio between volumes of incoming and outgoing water
through the system can be low, which can be a handicap if water is scarce in the area ( Dictor, et
al., 2004 ). Small structures may not be able to cope with the strong professional skills required
( Pedron, 2004 ). Precautions must be taken to avoid confusion between contaminated water,
treated water and concentrated solution. In other more basic solutions, concentrated by-products
are sludges or solids, which prevent any bad use.
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Coagulation assisted membrane filtration
After coagulation and flocculation, microfiltration is more effective than settling. Ultrafiltration can
be used after oxidation and flocculation.
Nanofiltration ( Sato, et al., 2002 )
This process is effective with a cut-off below 200 Daltons. Effectiveness depends on arsenic
oxidizing state (III or V) and recovery yields ( Welté and Montiel, 2004 ). Usually, other removed
compounds are required to justify this technique.
Reverse osmosis ( Ning, 2002 )
This process holds As (III) and As (V) but without specificity. Re-mineralization is generally
necessary after treatment. This solution is expensive and technical. Moreover, concentrated
solutions produced have to be disposed of ( Welté and Montiel, 2004 ). Costs for an individual unit
producing 100 l/day are between 10 and 15 €/m3 ( Cadic, 2002 ).
Electrodialysis ( Welté and Montiel, 2004 )
This process only holds ions. It is expensive and special professional skills are required. Treated
water could need mineralization and concentrated solutions are produced.
o BIOLOGICAL TECHNIQUES
Arsenic can encounter several modifications: biological oxidation, bio-methylation, biosorption or
modified by sulphate reducing process ( Simeonova, 2004 ). These processes can be
implemented in different ways - for instance sand filtration. It also works with any other media on
which a biofilm of arsenic oxidizing bacteria can develop ( Simeonova, 2004 ). Such a process
was initially designed for biological removal of iron and arsenic is in fact removed at the same
time ( Pedron, 2004 ).
Bacteria are present in sludges trapped in the filter. They are able to oxidize As (III) into As (V). In
Ambacourt, in the Vosges department, IRH Environnement designed a pilot as part of a RITEAU
program ( Dictor, et al., 2004 ). Both iron and arsenic were present in high levels in the water. An
addition of ferrous anions may be required ( Grapin, et al., 2002 ). Arsenic level was between 50
and 200 µg/l before treatment. This technique has many advantages. Sludges are easily
dehydrated and the filtration speed is high, which allows high flow rate. Moreover savings are
made on energy required for filter washing ( Katsoyiannis and Zouboulis, 2004 ).
Example 1: As (III) is oxidized by Thiobacillus ferroxidans ( AFSSA, 2004 )
Example 2: A few facts about biological removal of arsenic ( Pedron, 2004 )
50 m3/h and 600 m3/d (120 to 150 liters per day and per inhabitant, 4000 to 5000 inhabitants)
After an oxygenation of the raw water, the flow circulates in a sand column (100 cm long).
Filtration speed is 10 m/h, which makes 6 minutes to get through. A wash takes place every 3
weeks. Modifications were made to add ferrous ions Fe (II) to go through a second column. The
reaction takes place in the first half of the column, so that an addition of Fe (II) is possible in the
middle of the column. Fe (II) is oxidized in these conditions 20 times faster than As (III).
Example 3: Biological removal of both iron and arsenic is implemented in Wattwiller, in the HautRhin department. This treatment received approval from the AFFSA, the French agency for food
safety. It did not affect fluoride levels. ( AFSSA, 2002 ).
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Synthesis Arsenic Fluoride Lead
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MITIGATION TECHNIQUES FOR FLUORIDE
Most of basic techniques rely on precipitation, adsorption or ion exchange ( British Geological
Survey and WaterAid, 2002 ). Some authors think that there is no way to remove fluoride from
water at a reasonable price ( Fourcade and Sobole, 2003 ), if concentrations of fluoride in water
are too high, the best solution is to use another source or to try to dilute.
o PRECIPITATION
Aluminium or calcium salts can effectively precipitate fluoride ( Kayser, 2005 ). Reagents used are
lime Ca(OH)2, calcium sulphate CaSO4 or calcium chloride CaCl2. For instance, a treatment unit
creates hydroxides from aluminium sulphate. Solid matter aggregates to form flocs. These flocs
trap fluoride and they are removed together by filtration. This process is used in India in a
defluoridation plant ( Balaji). Decarbonatation also works.
The most famous technique is the Nalgonda technique, widely used in India: aluminium and lime
are added with calcium hypochlorite to disinfect. After flocculation and settling, the solution is
filtered. This technique can be used at a domestic level (in buckets) or at a larger scale in a water
treatment plant able to process several m3 ( British Geological Survey and WaterAid, 2002,
Nawlakhe and Bulusu, 1989 ). Costs for this technique are medium.
o ADSORPTION
The most effective treatments based on adsorption are activated alumina or bone charcoal
(activated charcoal produced by bone incineration). This last treatment is also effective on lead or
arsenic but is not always locally acceptable. It is also possible to use gypsum, dolomite or calcium
chloride to get treated water to conform with the standards (gypsum not tested). In South Africa,
gypsum reduces fluoride levels from 160 to 40 mg/l in water treated for irrigation ( Mazet, 2002 ).
Like activated charcoal and activated alumina, tricalcic phosphates can remove fluoride from
water ( Mazet, 2002 ). Decarbonatation with phosphates produces fluoroapatite providing a way to
remove fluoride. pH adjustment is important during decarbonatation.
o ION EXCHANGE
Water can be cycled through the ion exchange resin to remove almost all fluoride ( Simonnot). It
is possible only if another anion is predominant. The process is selective with a 100 % yield for
fluoride removal and a 90 % yield for restitution of other main ions. Tests were carried out at a
bench level but also at a pilot scale.
o MEMBRANE TECHNIQUES
In the presence of calcium, calcium fluoride CaF2 is formed and can be removed by nanofiltration.
Nanofiltration can be compared to a reverse osmosis at low pressure.
Reverse osmosis is a treatment for brackish water and can remove fluoride. A hydrostatic
pressure higher than 30 bar is applied on the side of the membrane where the concentrate is.
This pressure is greater than the osmotic pressure and water will go from the concentrated part to
the diluted part, on the other side of the membrane.
Electrodialysis is a separation involving an electrical field and selective membranes. With this
method, it is possible to reduce fluoride concentration.
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Synthesis Arsenic Fluoride Lead
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o OTHER TECHNIQUES
A biological cleanup of water is possible ( Latha, et al., 1999 ). The table below gives some
examples of Point-of-Use treatments ( Mariappan and Vasudevan, 2002 ).
Adsorption
Carbon materials
Wood, Lignite
Coal, Bone
Petroleum residues
Nut shells
Coffee husk, tea waste
Coconut shell
Carbion, Defluoron-1
Defluoron-2
Activated alumina
Bauxite
Clay minerals
Calcite
Bio-mass
Ion Exchange
NCL poly anion resin
Tulsion A27
Lewatit-MIH-59
Amberlite IRA-400
Deacedodite FF-IP
Waso resin-14
Polystyrene
hydroxisulphate
(PAHS)
Precipitation
Lime
Alum
Lime and Alum
(Nalgonda Technique)
Polyaluminium chloride
(PAC)
Others
Electrochemical
(Aluminium
electrode)
Electrodialysis
Reverse osmosis
MITIGATION TECHNIQUES FOR LEAD
There are fewer mitigation techniques for lead because it is rarely of natural origin. Treatments
usually mentioned consist in reducing water agressiveness or in protecting pipes. Replacement of
lead pipes or joins is also an option.
Point-of-Use units have been developed using adsorption and filtration.
The Générale des Eaux (Veolia Environnement) and the Department of
Hygiene and Research in Public Health (now IRH Environnement) in
Nancy (54) designed a filter ( Simonnot). The media is made of
activated carbon on synthetic zeolite. This process was tested on a
bench and at a pilot scale with 20 households in the Lorraine region.
(Picture by Générale des Eaux)
Many individual filters can be found and are not necessarily specially
designed to remove lead. For instance, Doulton filters for instance
remove
lead
and
other
metals
at
a
yield
better
than
98
%
(http://www.ideesmaison.com/eco/vel/eautraite.htm). Replacement cartridges cost 55 € every
2500 liters with an average price of 20 €/m3. This price should be compared with average price of
water in France (2.8 €/m3) and bottled water price (300 €/m3 on average for mineral or spring
water).
Activated charcoal exists under two forms: granular and solid block. For instance, a cartridge to
treat 120 to 150 liters costs between 4 and 8 euros, with an average of 40 €/m3 ( Johnson). The
flow rate is between 1 and 2 liters per minute ( IANR, 1997 ).
Individual reverse osmosis can remove up to 85 % lead and costs between 10 and 15 €/m3.
Distillation can remove up to 99 % lead ( IANR, 1997 ).
Page 12 out of 21
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MITIGATION TECHNIQUES FOR ARSENIC, FLUORIDE AND LEAD
o COMPATIBLE TREATMENTS
Combination of treatments to remove arsenic, fluoride and lead
The table above is a compilation of data from mitigation techniques of arsenic, fluoride and lead
taken individually. To remove both lead and fluoride, three techniques emerge: coagulation,
adsorption on activated alumina and reverse osmosis. To remove lead, individual filters exist and
they can sometimes remove fluoride or arsenic. These methods can be implemented in parallel or
series after pilot scale tests.
Page 13 out of 21
Synthesis Arsenic Fluoride Lead
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o TABLE OF MITIGATION TECHNIQUES FOR ARSENIC
Mitigation techniques for arsenic are presented in the two tables below ( CIRSEE, 2002, US EPA,
2000, US EPA, 2002 ). Some information also comes from a report from SOGEST (Vieux Ferrette
(68)).
Synthesis of mitigation techniques for arsenic (1st out of 2)
Page 14 out of 21
Synthesis Arsenic Fluoride Lead
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Synthesis of mitigation techniques for arsenic (2nd out of 2)
Page 15 out of 21
Synthesis Arsenic Fluoride Lead
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o TABLE OF MITIGATION TECHNIQUES FOR FLUORIDE
Synthesis of mitigation techniques for fluoride
( British Geological Survey and WaterAid, 2002 )
o EXAMPLES
Water characteristics have an influence on treatment effectiveness, especially pH or turbidity. The
pilot considered in the Nièvre department will monitor turbidity and eventually activate a bypass.
Tested processes are activated alumina and Granular Ferric Hydroxides. Ranking between these
two treatments is not yet defined (which one to use first). Arsenic reacts slower than fluoride. The
experiment is a long-term one, 3 to 6 months, to evaluate the impact of regeneration for activated
alumina or renewal for granular ferric hydroxide. A delay might be required after maintenance for
the system to be fully effective again. Lead mitigation is considered as a minor issue since only
one water resource among 6 contaminated is concerned ( Kayser, 2005 ). The contract has been
signed with IRH environnement and results are expected by September 2006.
There are Point-of-Use filters than can remove fluoride and lead ( Johnson). For instance, KDF
filters are made of a matrix containing an alloy of zinc and cupper. These filters also work with hot
water.
The CNRS and la société Européenne de Traitement des Eaux (ETE www.etefrance.com)
developed together a filter to remove arsenic and lead from drinking water ( CNRS, 2000 ). The
media is made of feldspath activated by heating. With this filter, lead levels dropped from 50 µg/l
to a few micrograms per liter. Two loads of 1 kg feldspath can clean 300 m3 of water, the average
consumption of a household per year. ETE centralizes regeneration or vitrification of the media.
The process is patented at a French and European level.
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Pilots removing arsenic and fluoride were tested at Three Forks (Montana, USA). Water
composition was less than 0.03 mg/l iron, 2.5 mg/l fluoride and 72 µg/l arsenic. An outsider won
the contest between four columns tested (see below): coagulation followed by membrane
filtration. Granular ferric hydroxides gave the best results of the four tested.
Volume treated per bed volume
Aquabind XP 2 : contains metallic oxides
1760 V/V
(Apyran technologies)
Alcan CPN (granular activated alumina)
2230 V/V
Alcan AA FS 50
2480 V/V
(iron coated activated alumina)
Granular ferric hydroxide
6370 V/V
Adsorption capacity of four materials ( US EPA, 2002 )
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Page 20 out of 21
APPENDICIES