Deflouridation: Importance and Techniques

7/29/2019 Deflouridation: Importance and Techniques

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IMPORTANCE ANDTECHNIQUES

DEFLUORIDATION

PRESENTED BY:

SANKET AGRAWAL

M.TECH 1ST YEAR, ENVIRONMENT ENGG.

ADVANCED WATER AND WASTEWATER TREATMENT


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DEFLUORIDATION: IMPORTANCE

Though water is regarded as a human right rather than a human need,the access to closer and cleaner drinking water is still a distant dream forabout one-sixth of humanity on this planet.


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CHEMICAL PROFILE

One Electron short to Inert gas configuration.

Most Electronegative and Reactive of all elements.Pale Yellow-Green Irritating gas.

0.3g/kg of Earths crust.

GEOCHEMISTRYRAIN WATER

CO2 FROM SOIL &AIR

LEACH SALTS (NaCl,NaHCO3)

FLOURIDE-BEARINGCOMPOUNDS via

FERTILIZERS

The alkaline water can mobilize F from soil ,

weathered rocks and CaF2.CaF2 + 2HCO3 CaCO3 + 2F + H2O + CO2

CaF2 has solubility product ofKsp= [F]2[Ca2+] = 4.0 1011

Waters with low content of calcium should have

high fluoride concentration.


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SOURCES OF FLUORIDE

NATURAL

CHIEF SOURCE: PARENT ROCK

(GRANITE ROCK 20-3600ppm)

SOIL

200-300ppm

FERTILISERS

FOOD

HIGH IN TEA PLANTS

1000 TIMES THAT OFSOIL

WATERHIGHEST: 2800ppm

SURFACE: 0.1-0.3

SEA WATER: 1.2-1.5

OTHER

INDUSTRIES

POWER PLANTS

CIGARATTES:236ppm

TEFLON-LINEDCOOKWARES:

3ppm

Average dietary intake of fluoride for adults living in area with 1.0ppm

fluoride in water is b/w 0.02-0.048mg/kg/day.

The presence of diet rich in calcium reduces the fluoride absorption in

human.


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GLOBAL SCENARIO

Affected (poisoned) morethan 25 nations across the

world.

More than 200 million

people across the globe are atrisk of fluorosis.

China more than 1/10th of population affected by fluorosis.

In Mexico, 5 million people(6% population) affected. In Ethiopian Rift Valley fluoride conc. in range of1.5 to 177 ppm

encountered.

Tanzania (8-12.7ppm) most severely affected country. (Acc. to

WHO (1-1.5ppm)standards nearly 30% water sources are unfit.)


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INDIAN SCENARIO

20 States affected.

Affecting more than 66 million peopleincluding 6 million children

under 14 years age.

One of the most alarming public health

problem of the country.

Rajasthan, Andhra Pradesh and Assam

are most endemic.

People of Rajasthan and Assam are

forced to consume water with fluorideconcentration up to 44ppm and 23ppm,

resp.

Delhi has natural maximum fluoride concentration of

32ppm.


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EFFECTS

Dental Effects

DENTAL CARIES

DENTALFLUOROSIS

Skeletal

Effects

SKELETALFLUOROSIS

Other AdverseEffects

CARCINOGENICITY

GASTROINTESTINALEFFECTS

EFFECTS OF FLUORIDE

Fluoride has both beneficial and detrimental effects on human health with

only a narrow range between intakes that are associated with these

effects.


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DENTAL CARIES(Tooth Decay)

Dental caries is an infectious and multifactorial

disease causing demineralization of inorganiccomponents of teeth. Untreated caries can lead to:

Incapacitating pain

Bacterial infection

Tooth extraction

Loss of dental function.

WHO permissible limits for preventing Dental Caries is 0.5-1.2ppm.

CDC hails water fluoridation as one of the ten most important public health

measures currently available.

Globally, the population consuming fluoridated drinking water were estimated as

about 355 million in 2005.

Fluoride aids the calcium and phosphate ions chemical reaction producing

a crystal surface much less soluble in acid enhancing remineralization.


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DENTAL FLUOROSIS

Irreversible toxic effect on the tooth

forming cells

It ranges from barely visible whitestriations on the teeth through to gross

defects and staining of the enamel.

The calcium rich constituents of teeth, viz. enamel and dentin, have strong affinity

for fluoride during the formation of teeth.

Fluoride combines with calcium forming calcium fluoroapatite crystals during

mineralization.

So, as fluoride accumulates, calcium is lost from the teeth.

Due to loss of calcium, enamel becomes more porous, discolored and prone to wear.

MECHANISM

EFFECTS

unfavorable effects on individuals personality.

It is hard to smile for a person with dental fluorosis.

Inferiority complex, likely to experience embarrassment, isolation and discrimination.

Can lead to deep psychological depression.


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SKELETAL FLUOROSIS

Fluoride replaces the hydroxyl ion from hydroxyapatite, a mineral phase during formation

of bone forming hydroxyfluorapatite, altering the mineral structure of bones this leads

to the formation of denser bones which are more fragile and brittle.

Occurrence of fluorosis depends upon many factors like nutritional status and diet, climate,

amount of exposure, source of fluoride intake, etc. (observed even in range of0.4-1.4ppm)

Physical Effects: kyphosis, scoliosis, paralysis, deafness, Genu vaum (bow legs),

etc.

Social Effects: loss of work & livelihoods, psychological trauma, impaired

marriage possibilities for girls, inability to meet high medical costs and above

all, the loss of will to live.


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DEFLUORIDATION TECHNIQUES

The lack of excess to clean water denies the most essential of allrights, the right to life


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CLASSIFICATION

COAGULATIONTECHNIQUES

PRECIPITATION

(LIME , CaSO4)

COPRECIPITATION

(BY ALUM & LIME)

ADSORPTION/ION EXCHANGE

BY BONE, BONECHAR,CLAYS

ACTIVATEDALUMINA

ELECTROCHEMICALMETHODS

ELECROCOAGULA-TION

ELECTROSORPTION

MEMBRANEMETHODS

REVERSEOSMOSIS

ELECTRODIALYSIS

NANO FILTRATION

DEFLUORIDATION TECHNIQUES


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NALGONDA TECHNIQUE

(Alum-lime Co-precipitation)

It involves addition of alum, lime, and bleaching

powder to raw water.Sodium aluminates or lime hastens the

settlement of precipitate and bleaching powder

insures disinfection.

Fluoride get adsorbed on sticky gelatinous

Al(OH)3 flocs during sweep coagulation.

Al+3 +H2O Polynuclear-Hydroxo Complexes + H+

H+ ions will neutralize the alkalinity.

If initial alkalinity is low there will be further

reduction buffering capacity destroyed pH

drop rapidly.

But alkalinity is must for hydroxide floc

formation.

Hence artificial alkalinity in the form of lime or

soda ash is added with the alum.Fig. Domestic Treatment

Precipitation Settling Filtration


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ADVANTAGES

The absence of regeneration of media

Use of readily available chemicals.

Easy operation and maintenance.

Low cost chemicals used.

Simultaneous removal of color, odor, turbidity, bacteria, and organic

contaminants.

DISADVANTAGES

Did not achieve a great degree of success in field applications both as

hand-pump-based units and as smaller domestic units.

Medium efficiency (

70%).Large dose requirement of aluminum sulfate (7001200 mg/L).

Difficulty in controlling alum and lime dosages for different sources.

High hardness of the treated water.

Increased pH.


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ELECTRODIALYSIS

The removal of ionic components from aqueous solution through ion

exchange membranes is carried out under the driving force of anelectrical field.

C(-) A(+) A(+)

CONCENTRATECONCENTRATE


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SELECTION OF ELECTRODIALYSIS MEMBRANE

Permselectivity,A low water transport number,

Reasonably good electrical conductivity,

Good chemical resistance especially to oxidation,

Adequate mechanical strength,

Dimensional stability.

Perfluorosulfonic acid polymer: Nonporous ,Isotropic, 50500 Poly(styrene-co-divinylbenzene ): Nonporous, Isotropic, 100500

ACS-CMX membranes: Monovalent Anion Permselective

MEMBRANES USED


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EFFICIENCY

Current efficiency is a measure of how effective ions are transported

across the ion exchange membranes for a given applied current.

5000 mg/L TDS and fluoride up to 15 mg/L can be reduced to600 mg/L

TDS and


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ADVANTAGES

Simultaneous defluoridation and desalination of brackish water.

Commercially established.More economical than pressure driven processes.

More resistant to fouling ( Electrodialysis Reversal Systems).

High capacity.

Less space requirement.

LIMITATIONS

Require high degree ofpretreatment.

Ineffective in removing low-molecular-mass non-charged compounds.Not suitable for waters oflow salinity (conductivity < 0.5 Ms).

Disposal of concentrate: (Dilution in saline water, deep well storage,

combustion, industrial reuse, etc.)


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REFERENCES

Ayoob, S. & Gupta, A.K. (2006) Fluoride in Drinking Water: A Review on

the Status and Stress Effects. Critical Rev. Environ. Sci. Technol.

Ayoob, S., Gupta, A.K. & Venugopal, T.B. (2008)A conceptual overview

on sustainable technologies for defluoridation of drinking water, Critical

Rev. Environ. Sci. Technol.

Frederick B. &Daniel E.(2009) Defining the concentrate disposal problemand identifying potential solutions. Critical Rev. Environ. Sci. Technol.

Turnbull S., Benning F., G. W. Feldmann, Linch L., Mc Harness, &

Richards S.Analysis and disposal of fluorine. Industrial and engineering

chemistry. Vol.39, No.3.

Adhikary, S.K., Tipnis, U.K., Harkare, W.P., and Govindan, K.P. 1989.

Defluoridation During Desalination of Brackish Water by Electrodialysis.

Desalination,71, 301312

Electrodialysis Source: http://en.wikipedia.org/w/index.php?

oldid=498361104.


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Deflouridation: Importance and Techniques