This document discusses techniques for defluoridation of water, including adsorption using materials like activated carbon, bone charcoal, and alumina. It also discusses ion exchange resins and precipitation techniques like the Nalgonda method using lime and alum. The Nalgonda technique is effective at removing fluoride from 1.5-20 mg/L and has benefits like low cost, simple design, and simultaneous removal of other contaminants without regeneration requirements. Defluoridation is important for treating drinking water to prevent dental fluorosis from high fluoride levels.

1. Water deflouridation

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Contents
 INTRODUCTION
 DEFINITION
 CHARACTERISTICS OF DEFLUORIDATION PROCESS
 TECHNIQUES
 CONCLUSION
 REFERENCES

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Introduction
 Fluorine is the 13th most abundant naturally occurring
element in the Earth’s crust.
 It is the most electronegative and reactive of all the
elements and as a result, elemental fluorine does not
occur in nature but found as a fluoride mineral
complexes.

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 Water is frequently referred to as a universal solvent,
because it has the ability to dissolve almost all
substance; that comes in its contact. Some elements are
essential in trace amount for human being while higher
concentration of the same can cause toxic effects.
Fluoride is one of them.

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 Due to rapid urbanization and growth of modern
industries as well as geo chemical dissolution of
fluoride bearing minerals, fluoride concentration is
increasing in the environment including water
resources. The high concentration in the drinking
water leads to destruction of enamel of teeth and
causes a number of conditions referred to
collectively as fluorosis.

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 The process of water treatment that reduce the
concentration of fluoride in the water, in order to
make it safe for human consumption is
DEFLUORIDATION.
 Defluoridation is used to characterize methods
that reduce the fluoride ion specifically, without
major other changes to the quality of the treated
water.

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DEFINITION
 Community Water Defluoridation is defined as
The downward adjustment of fluoride ion
concentration in public drinking water supply so
that the level of fluoride is maintained at the normal
physiological limit of 1 ppm to prevent dental
caries with minimum possibility of causing dental
fluorosis.

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characteristics of defluoridation
process:
 1) Cost effective
 2) Easy to handle or operate by the people.
 3) Independent of input fluoride concentration
alkalinity, pH, temperature.
 4) Not affect taste of water.
 5) Not add other undesirable substances (eg.
Aluminium) to treated water.

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History
 Practical experience in defluoridation
1) Britton, South Dakota, USA :
 This community of 1430 persons received water
containing on average, 6.7 ppm F.
 On 20 November 1948 a defluoridation plant became
operational using synthetic hydroxyapatite.

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 However it was only partially effective, reducing
the water fluoride level to 3.6 ppm instead of the
target level of 1.5 ppm , and because of this and
because of excessive loss of material , the plant
was closed after 4 years use.
 Bone char replaced hydroxyapatite and the
defluoridation recommenced in January 1953.

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2) Bartlett , Texas USA :
 Bartlett is a small community with a population of less
than 2000 in 1952 when it was decided to defluoridate
the public water supply which had one of the highest
fluoride levels in the USA (8.0 ppm) .
 The defluoridation plant was installed by the US
Public Health Service and used activated alumina , in
an insoluble granular form.

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 It was designed to reduce the fluoride level from
8.0 to 1.0 ppm .The alumina was periodically
reactivated.
 The plant functioned well during the first 11 years
( 1952 – 1963) more than 6500 water samples were
obtained from the distribution system indicating
an average fluoride level of 1.1 ppm.

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3) India :
 Much development work has been undertaken by NEERI
at Nagpur.
 A pilot plant using the ion exchange resins carbion and
defluoron – 1 commenced at Gangapur (Rajasthan).
Aluminium solution was used as regenerant, but the
system was unsuccessful as most of the defluoron – 1 was
washed out.

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 To overcome these problems, defluoron – 2 was
developed in 1968. It is a sulphonated coal using
aluminium solution as regenerant .Two plants,
each of 20000 Imp.gal capacity per regeneration,
have been installed.
 But the regeneration and maintenance of the plant
required skilled operation.

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 In response to this drawback, NEERI developed
the Nalgonda technique.
 A defluoridation plant using the Nalgonda
technique was commissioned in the town of Kadiri
in Andhra Pradesh in 1980 to treat water
containing 4.1 – 4.8 mg F/l. It had a capacity of
2270 m3/ day and served the population of 34000.

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 The inclusive cost of treating the water was
calculated at 1 rupee /L.
 Subsequently visitors reported that the operation
and maintenance of the plant had declined, and
this was confirmed by NEERI during two visits in
1984 – 1986.

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Techniques
 Adsorption
 Ion-exchange
 Precipitation
 Others

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Adsorption
 Carbon materials,
 Activated Alumina,
 Magnesia,
 Wood,
 Tricalcium phosphate, Calcite, Hydroxy apatite
 Activated charcoal, Fish bone char,
 Processed bone,
 Nut shells,
 Paddy husk, Coffee husk,
 Tea waste, Jute waste, Fly ash.

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Ion-exchange
 Anion exchange
resins:
 NCL poly anion resin
 Tulsion A27,
 Deacedodite FF-IP
 Waso resin-14
 Polystyrene.
 Cation exchange
resins:
 Defluoron-1
 Defluoron-2
 Carbion

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Precipitation
 Lime
 Alum
 Lime & Alum (Nalgonda technique)
 Alum flock blanket method
 Poly Aluminium Chloride (PAC)
 Poly Aluminium Hydroxy Sulphate (PAHS)
 Brushite.

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Others
 Electrochemical method (Aluminium electrode)
 Electro dialysis
 Electrolysis
 Reverse Osmosis.

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1) BASED ON ADSORPTION PROCESS:
 These include several bone formulation, synthetic
tri-calcium phosphate & hydroxy appatite and a
variety of Adsorbent materials.

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A) ACTIVATED CARBON
 Prepared from :- Paddy Husk
 Has high defluoridation capacity
 Similarly activated carbon prepared from cotton waste.

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B) BONE CHARCOAL
 Method for preparation:
 Dried & crushed bone is heated to 600 0C for 20 min.
 Efficient fluoride renewer (fluoride renewal capacity
1000mg/l)
 Bone charcoal is preferred over natural bone because:-
 Bacterial Contamination is reduced.
 Taste is improved
 Bone charcoal can be regenerated with caustic soda.
 Disadvantage:-
 Use of bone is unacceptable to some religious groups.

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ANIMAL BONE FOR DEFLUORIDATION

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C) PROCESSED BONE
 Bone contains calcium phosphate and has a great
affinity for fluoride.
 Bone is dried & powdered.
 Powered Bone can be used as a contact bed for
removal of fluoride in drinking water.
 Advantage:- Exhausted bed can be regenerated
with sodium hydroxide solution.

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D) TRI – CALCIUM PHOSPHATE
NATURAL SYNTHETIC
Prepared synthetically by reacting
milk of lime & Phosphoric Acid
E) ACTIVATED MAGNESIA:
 It is a good adsorbent among several substances.
 It has better fluoride removal capacity at high
temperature.
F) TAMARIND GEL:
 - Concentration of fluoride from solution of
sodium fluoride of 10mg/L can be reduced up to-
 a) 2mg/L by addition of tamarind gel alone and.
 b) 0.5mg/L by addition of small quantity of chlorine
with tamarind gel .

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G) SERPENTINE:
 It is the name which suggest or that applies to the
mineral containing one or both the minerals-
 Chrysolite.
 Antigorite.
 Yellow mineral was found to have better fluoride
removal capacity than green minerals.
 Drawback- medium can not be regenerated and has
to be discarded after use.

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H) ACTIVATED ALUMINA-
 - Method of choice in developed countries.
 - Its affinity for fluoride is very high.
 - It is a porous material with a surface comprised
largely of active site.
 METHOD OF PREPARATION
 Aluminum hydroxide [ Al(OH)3].
[ dehydration 300-600 0c]
Activated alumina
 - Excellent method for fluoride removal.

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Defluoridation Activated
Alumina

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ADVANTAGE &DISADVANTAGE
 Exhausted material is regenerated by washing with
alkali, followed by acid & finally with distilled water.
 It requires minimum contact therefore maximum
defluoridation.
 Cost effective.
 Defluoridation capacity at natural PH is appreciable.
 Its defluoridation capacity is independent of
temperature.

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 The effect of other ions present in drinking water, like
chlorides, sulphates, carbonates is minimum over
defluoridation efficiency of activated alumina,in spite of the
presence of bicarbonate ions which show considerable
influence in process of defluoridation.
 BUT
 Control of PH & alkalinity is crucial when activated alumina
used.

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I) BURNT CLAY-
Obtained from -: Brick chula.
Prepared by -: Burning a mixture of 70% clay + 30%
red sail clay with particle size = 500 micron exhibited
maximum defluoridation efficiency.
At low PH range defluoridation efficiency was more
compared to that at high PH range.

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BURNT CLAY FILTER

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II) BASED ON ION EXCANGE MECHANISM
A) ANION EXCHANGE B) CATION
EXCHANGE
RESINS RESINS
 A) ANION EXCHANGE RESINS-:
 Removes fluorides either by hydroxyl cycle or
chlorine cycle along with other anions.Eg :-
 Polyanion exchange resin.
 Tulsion A-27
 Deacodite FF
 Lawatit MH-5a

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B) CATION EXCHANGE RESINS:-
1) DEFLUORON-1
 A sulphonated saw dust impregnated with 2% alum solution.
2) CARBION
 It is a cation exchange resin of good durability and can be used
on sodium & hydrogen cycles.
3) MAGNESIA
 It removes the excess Fluoride but PH of treated water is beyond
10 & its correction by acidification or recarbonation is necessary.

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4) DEFLUORON -2
 This was developed in 1968.
 It is a sulphonated coal & works on the aluminum
cycles.
 Cation exchange resins impregnable with alum
solution acts as “ Defluoridating Agents”
“AVARAM BARK”
 Based on cation exchange resin works effectively in
removing fluoride from water.

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Avaram Bark Filter.

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III) BASED ON CHEMICAL REACTION
1) LIME:-
 Lime has affinity with fluoride & can be used for
removal of excess fluoride from water.
MECHANISM:-
 Lime + Water containing Mg. salts.
 Fluoride is adsorbed on magnesium hydroxide flocs
 Results in fluoride removal.
DISADVANTAGE
 Control of PH is crucial.
 Method is only reasonable when removal of both
hardness & fluoride is required.

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2) NALGONDA TECHINQUE:-
Nalgonda technique was named after the village in India
where the method was pioneered.
 Principle Employed:- Flocculation principle.
 Developed at:- National Environmental Engineering
Research Institute [NEERI] at Nagpur in 1974.

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MECHANISM OF DEFLURIDATION BY
NALGONDA TECHNIQUE :-
1) RAPID MIXING:-
 Carried out at 10-20 r.p.m for 30 sec.
 The coagulant is rapidly and uniformly dispersed through out
single or multiple phase system.
 This help in formation of microflocs and results in proper
utilization of chemical coagulant
2) CHEMICAL INTERACTION:-
► In this sodium aluminates or lime, bleaching powder are added
in sequence and the alum is filtered to fluoride water.

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3) FLOCCULATION
► It is the stage of formation of settable particles (flocs) from
destabilized colloidal size particles.
► Achieved by gentle and prolonged mixing for 10-15 min at 2-4
r.p.m.
4) SEDIMENTATION:-
In this the suspended particles [ Heavier than water] are
separated from water by gravitational setting.

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5) FILTRATION:-
 It is a process for separating suspended & colloidal impurities
from water by passage through porous media.
6) DISINFECTIONS:-
 Done by – Halogens [ chlorination– most
efficient method.]
- Ozone
- UV rays
7) SLUDGE CONCENTRATION:-
 To recover water & aluminum salts.

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SALIENT FEATURES OF NALGONDA TECHNIQUE
 No regeneration of Media
 No handling of caustic soda and alkalies
 Readily available chemicals used in conventional
municipal water treatment are only required.
 Adaptable to domestic use.
 Simplicity of design, construction ,operation and
maintenance.

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 Highly efficient, removal of fluoride from 1.5 to 20 mg
fluoride /l to desirable levels.
 Simultaneous removal of color, odour, turbidity,
bacteria and organic contaminants.
 Sludge generated in convertible from can be used else
where.
 Little wastage of water & least disposal problem.
 Needs minimum of Mechanical & Electrical Equipment.
 No energy except muscle power for domestic
equipment.

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INDICATIONS FOR ADOPTING NALGONDA
TECHNIQUE
 Absence of acceptable, alternate low fluoride
source within transportable distance.
 Total dissolved solids are below 1500 mg/l ;
desalination may be necessary when the total
dissolved solids exceeds 1500 mg/l.
 Raw water fluoride ranging from 1.5 mg. to 2 mg
fluoride/l.
 Nalgonda technique is effective even when the
dissolved solids are above 1500 mg/l and hardness
above 600mg /l.

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DOMESTIC TECHNIQUE
 A container of 20-50 liters of water is treated with lime
water + Bleaching Powder
Mixed well
 Alum is poured & stirred for 10 min.
 Contents are allowed to settle for 1 hr and clean water is
withdrawn without disturbing the sediment.
FILL AND DRAW TYPE DEFLUORIDATION PLANT
 For small communities.
 Procedure and materials are same as that for domestic
technique only the quality of water is more.
By Sparkling

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PRACTICAL EXPERIENCE IN
DEFLUORIDATION
 India has extensive areas of endemic fluorosis and
there is a need of comprehensive mapping of
fluoride level in drinking water.
 Much development has been undertaken by NEERI at
Nagpur.
 Systems which looked promising were investigated
in pilot studies.
 A pilot plan using ion exchange resins carbion and
defluoron -1[8:1Proportion] was commenced at
Gangapur (Rajasthan)
 Aluminum solution was used as a regenerant there,
but the system was unsuccessful, as most of the
defluoron -1 was washed out.

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 To over comes these problems defluoron-2 was
developed. No details of effectiveness or cost have
been obtained although, defluoron – 2 was reported
to be successful in removing fluorides but the
regeneration and maintenance of plant required
skilled operation which was not readily available.

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 Problem of cost & availability of equipment and materials and
the lack of trained personnel for plant maintenance in some
areas have seemingly prevented widespread introduction of
water defluoridation.
 In response to this drawback, NEERI developed the Nalgonda
technique.
 Cost of water defluoridation using Nalgonda technique is about
1.5 to 3 times the cost of untreated water, although it is likely to
be much cheaper than transporting water over long distance.

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Dengaon Defluoridation Plant in Karbi Anglong

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CONCLUSION
 Drinking water is the main source of ingestion of fluoride.
 Defluoridation should be taken up where there is no alternate
source of safe drinking water.
 Governments should establish the community defluoridation
plants and sanction sufficient funds for their maintenance.
 The advantage of the community defluoridation over
domestic defluoridation is uniformity of the procedure and
hence, better quality control.
 Where community defluoridation is not feasible, the residents
of the endemic fluorosis areas should be educated and
motivated to adopt domestic defluoridation techniques.

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REFERENCES
Guide line for drinking water quality
- Second Edition (Vol.- 3) WHO Geneva.
Renuka P et al. review on water deflouridation. The
International Journal Of Engineering And Science
2013;2 (3): 86-94.
Eswar P . Water Deflouridation. IJDA 2011; 3(2)
Essentials of Preventive & community dentistry
- 3rd Edition – Soben Peter
Textbook of community dentistry
- Staish Chandra
- Shaleen Chandra

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