Upload
dangphuc
View
219
Download
0
Embed Size (px)
Citation preview
Introduction
Page | 1
Introduction
Fluorine, the 13th most abundant element of the earth’s crust, represents
about 0.3g / kg of earth’s crust. Its molecular weight is 19 and atomic number is
9. It occurs mainly in the form of chemical compounds such as sodium fluoride or
hydrogen fluoride, which are present in minerals fluorspar fluorapatite, topaz and
cryolite. The physicochemical properties of fluorides available in the form of
sodium fluoride and hydrogen fluoride are given in Table. 1.1. In India, fluorite
and topaz are widespread and contain a high percentage of fluoride. Fluoride
pollution in the environment occurs through two channels, namely natural and
anthropogenic sources (Cengeloglu et al. 2002).
Fluoride is frequently encountered in minerals and in geochemical
deposits and is generally released into subsoil water sources by slow natural
degradation of fluorine contained in rocks. Fluorine is an important element for
human beings, as it helps in growth and prevents the enamel of the teeth from
dissolving under acidic conditions. Various dietary components influence the
absorption of fluorides from gastrointestinal tract and the absorbed fluorides are
distributed throughout the body. Drinking water and sea food are good sources of
fluoride. Fluoride is beneficial to health if the concentration (CF) of the fluoride
ion (F-) in drinking water is less than 1.5 mg/L (WHO 1994).A higher
concentration causes serious health hazards. The disease caused manifests itself in
three forms, namely, dental, skeletal, and non-skeletal fluorosis. Dental fluorosis
produces widespread brown stains on teeth and may cause pitting (Bulusu and
Nawlakhe, 1992). Skeletal fluorosis causes crippling and severe pain and stiffness
of the backbone and joints (Bulusu and Nawlakhe, 1992). Even though extensive
studies have been conducted, there seems to be no effective cure for these
diseases. Therefore, it is desirable to drink water having a fluoride concentration
Introduction
Page | 2
less than certain value. Hence, drinking water with CF > 1.5 mg/L (1 mg /L in
India) needs treatment (WHO1994).
Table1:1 Physiochemical properties of common forms of fluoride
Property Sodium Fluoride
(NaF)
Hydrogen Fluoride
(HF)
Physical state White, crystalline powder
Colour less liquid or gas with biting smell
Density (g/cm3) 2.56 _
Water solubility 42g/L at100 C Readily soluble below 200C
Acidity _ Strong acid in liquid form; weak acid when
dissolved in water
Source: (Pranab Kumar Rakshit, 2004)
1.1 Fluoride in water: An overview
Throughout many parts of the world, high concentrations of fluoride
occurring naturally in groundwater and coal have caused widespread fluorosis - a
serious bone disease - among local populations. A range of everyday products,
notably toothpaste and drinking water, the fluoride in small doses has no adverse
effects on health to offset its proven benefits in preventing dental decay. But more
and more scientists are now seriously questioning the benefits of fluoride, even in
small amounts (UNICEF Report, 1980). Since some fluoride compounds in the
earth's upper crust are soluble in water, fluoride is found in both surface waters
and groundwater. In surface freshwater, however, fluoride concentrations are
usually low - 0.01 ppm to 0.3 ppm.
In groundwater, the natural concentration of fluoride depends on the
geological, chemical and physical characteristics of the aquifer, the porosity and
acidity of the soil and rocks, the temperature, the action of other chemical
elements, and the depth of wells. Because of the large number of variables, the
Introduction
Page | 3
fluoride concentrations in groundwater can range from well under 1 ppm to more
than 35 ppm. In Kenya and South Africa, the levels can exceed 25 ppm. In India,
concentration up to 38.5 ppm has been reported in drinking water (UNICEF).
Table1:2 Permissible limit of fluoride in drinking water prescribed by
various organizations
Name of the organization Desirable limit (mg/L)
Bureau of Indian Standards (BIS) 0.6-1.2
Indian Council of Medical Research (ICMR) 1.0
The Committee on Public Health Engineering
Manual and Code of Practice, Government of India
1.0
World Health Organization (International
Standards for Drinking Water)
1.5
1.2 Basic facts about fluoride:
Fluoride exists fairly abundantly in the earth's crust and can enter
groundwater by natural processes; the soil at the foot of mountains is particularly
likely to be high in fluoride from the weathering and leaching of bedrock with
high fluoride content.
According to 1984 guidelines published by the World Health Organization
(WHO) fluoride is an effective agent for preventing dental caries if taken in
'optimal' amounts. But a single 'optimal' level for daily intake cannot be agreed
because the nutritional status of individuals, which varies greatly, influences the
rate at which fluoride is absorbed by the body. A diet poor in calcium, for
example, increases the body's retention of fluoride.
Introduction
Page | 4
Water is a major source of fluoride intake. WHO (1984, guidelines)
suggested that, areas with a warm climate, the optimal fluoride concentration in
drinking water should remain below 1 mg/liter (1ppm or part per million), while
in cooler climates it could go up to 1.2 mg/liter. The differentiation derives from
the fact that we perspire more in hot weather and consequently drink more water.
The guideline value (permissible upper limit) for fluoride in drinking water was
set at 1.5 mg/liter, considered a threshold where the benefit of resistance to tooth
decay did not yet shade into a significant risk of dental fluorosis.
In many countries, fluoride is purposely added to the water supply,
toothpaste and sometimes other products to promote dental health. It should be
noted that fluoride is also found in some foodstuffs and in the air (mostly from
production of phosphate fertilizers or burning of fluoride-containing fuels), so the
amount of fluoride people actually ingest may be higher than assumed.
It has long been known that excessive fluoride intake carries serious toxic
effects. But scientists are now debating whether fluoride confers any benefit at all.
1.3 Fluoride: good or bad for health?
Fluoride was first used to fight dental cavities in the 1940s, its
effectiveness defended on two grounds:
• Fluoride inhibits enzymes that breed acid-producing oral bacteria whose
acid eats away tooth enamel. This observation is valid, but some scientists
now believe that the harmful impact of fluoride on other useful enzymes
far outweighs the beneficial effect on caries prevention.
• Fluoride ions bind with calcium ions, strengthening tooth enamel as it
forms in children. Many researchers now consider this more of an
assumption than fact, because of conflicting evidence from studies in India
and several other countries over the past 10 to 15 years. Nevertheless,
Introduction
Page | 5
agreement is universal that excessive fluoride intake leads to loss of
calcium from the tooth matrix, aggravating cavity formation throughout
life rather than remedying it, and so causing dental fluorosis. Severe,
chronic and cumulative overexposure can cause the incurable crippling of
skeletal fluorosis (A.Tiwari et.al. 2009).
1.4 Symptoms of Fluorosis:
Dental fluorosis, which is characterized by discolored, blackened, mottled
or chalky-white teeth, is a clear indication of overexposure to fluoride during
childhood when the teeth were developing. These effects are not apparent if the
teeth were already fully grown prior to the fluoride overexposure; therefore, the
fact that an adult may show no signs of dental fluorosis does not necessarily mean
that his or her fluoride intake is within the safety limit.
Chronic intake of excessive fluoride can lead to the severe and permanent
bone and joint deformations of skeletal fluorosis. Early symptoms include
sporadic pain and stiffness of joints: headache, stomach-ache and muscle
weakness can also be warning signs. The next stage is osteosclerosis (hardening
and calcifying of the bones), and finally the spine, major joints, muscles and
nervous system are damaged.
Whether dental or skeletal, fluorosis is irreversible and no treatment exists.
The only remedy is prevention, by keeping fluoride intake within safe limits.
1.5 Fluorosis worldwide:
The latest information shows that fluorosis is endemic in at least 25
countries across the globe (Figure1.1). The total number of people affected is not
known, but a conservative estimate would number in the tens of millions. In 1993,
15 of India's 32 states were identified as endemic for fluorosis. In Mexico, 5
Introduction
Page | 6
million people (about 6% of the population) are affected by fluoride in
groundwater. Fluorosis is prevalent in some parts of central and western China
and caused not only by drinking fluoride in groundwater but also by breathing
airborne fluoride released from the burning of fluoride-laden coal. Worldwide,
such instances of industrial fluorosis are on the rise (UNICEF).
Some governments are not yet fully aware of the fluoride problem or
convinced of its adverse impact on their populations. Efforts are therefore needed
to support more research on the subject and promote systematic policy responses
by governments.
Endemic Fluorosis in different countries of the world (UNICEF)
Figure 1.1
Introduction
Page | 7
1.6 Fluoride in India:
India is among the many countries in the world, where fluoride
contaminated ground water is creating health problems. Safe drinking water in
rural areas of India is predominantly dependent on groundwater sources, which
are highly contaminated with fluoride. The concentrations in 17 States out of 32
are endemic for fluorosis being 1 to 48 mg/L. About 62 million people including
6 million children are affected with dental, skeletal and non-skeletal fluorosis.
This involves about 9000 villages affecting 30 million people (Nawlakhe
and Paramasivam, 1993). It must be noted that the problem of excess fluoride in
drinking water is of recent origin in most parts. Digging up of shallow aquifers for
irrigation has resulted in declining levels of ground water. As a result, deeper
aquifers are used, and the water in these aquifers contains a higher level of
fluoride (Gupta and Sharma, 1995).
In India, the states of Andhra Pradesh, Bihar, Chhattisgarh, Haryana,
Karnataka, Madhya Pradesh, Maharashtra, Orissa, Punjab, Rajasthan, Tamil
Nadu, Uttar Pradesh and West Bengal are affected by fluoride contamination in
water.
Worst affected: - Rajasthan and Gujarat in North India and Andhra in South
India.
Moderately affected: - Punjab, Haryana, M.P. and Maharashtra.
Mildly affected: - T.N., W.B., U.P., Bihar and Assam.
Introduction
Page | 9
1.7 Fluoride in Rajasthan:
In Rajasthan the existence of fluorides was first detected in 1964 when a
survey was under taken by state PHED in collaboration with NEERI on the basis
of reports of some peculiar diseases. The concentration in ground water varied
from as low as zero to 18.00ppm as maximum.
Fluorides make an entry in drinking water from indigenous rocks and
ground water around the mica mines (Rajasthan has rich sources of mica). In the
absence of perennial rivers, surface and canal system, groundwater remains the
main source of drinking water. It contains 2 to 20 mg/L of fluoride .Fluoride is
more common in ground water than in surface water. The main sources of
fluoride in ground water are different fluoride bearing rocks .Fluoride ions are
important in water supplies because of their peculiar characteristics. They cannot
be tolerated in too low or too high concentration. A Fluoride concentration of
approximately 0.5mg/l to 1mg/l in drinking water effectively reduces dental caries
or tooth decay without any harmful effects on health. Excess concentration of
fluoride (more than 2mg/l) causes dental fluorosis (disfigurement of the teeth) and
harm to bony structures.
All the 32 districts of Rajasthan affected are from fluorosis. Nagour,
Jaipur, Sikar, Jodhpur, Barmer, Ajmer, Sirohi, Jhunjhnu, Churu, Bikaner,
Ganganagar districts have been declared as fluorosis prone areas. People in
several districts in Rajasthan are consuming water with fluoride concentrations up
to 24 mg/l. Rajasthan has more than 51 per cent of the affected villages in the
country. The number of villages affected by fluoride has increased over time. In
1973, there were 1,871 villages with fluoride levels over 3mg/l. By 2001, this
number had risen to 10,342 villages, an increase of more than five times. This
makes Rajasthan the most severely affected state in India, with millions crippled
as the result of consuming excessive amounts of fluoride (State Institute of Health
and Family Welfare, Jaipur)
Introduction
Page | 11
1.8 Various Health Impacts of Fluoride:
Fluoride being an electronegative element and having a negative charge is
attracted by positively charged ions like calcium (Ca++). Bone and tooth having
highest amount of calcium in the body attracts the maximum amount of fluoride
and is deposited as Calcium Fluorapatite crystals. Intake of fluoride above 1.5
mg/L may lead to serious manifestations, which are described below:-
1.8.1 Dental fluorosis:
Incidences of mottled teeth have been observed even with range of 0.7 –
1.5 mg F / l in drinking water. The minimal daily intake of fluoride that can cause
very mild or mild fluorosis is estimated to be about 0.1 mg/kg body weight (P.
Singh et.al.2011).Dental fluorosis is the loss of luster and shine of the dental
enamel. The discoloration starts from white yellow, brown to black.
(Discoloration is either as spots or horizontal streaks). Enamel matrix is laid down
on incremental lines before and after birth. Hence dental fluorosis is invariably
seen on horizontal lines or on bands on the surface of the teeth .Fluorosis is seen
as mild, moderate and severe depending on the amount of fluoride ingested during
the stages of formation of the teeth.
Teeth commonly affected by fluorosis are central incisors, lateral incisors
and the molars of the permanent dentition. It affects both the inner and the outer
surfaces of teeth.
The symptoms of dental fluorosis are as given below:
1. Loss of teeth at early age.
2. Dullness of the teeth and loss of shine with developed white and yellow
spots.
Introduction
Page | 12
3. Discoloration of teeth, turning into brown and black streaks or spots on the
enamel surface.
4. The teeth, once affected by dental fluorosis, cannot be reversed to normal.
Only discolored teeth can be masked by the methods as prescribed below:
Bleaching of teeth, Filling with high cure material and laminated
veneering. Capping or crowning of teeth with metals like chrome, cobalt,
gold, porcelain and acrylic.
1.8.2 Skeletal fluorosis:
Excessive quantity of fluoride deposited in the skeleton , which is more in
cancellous bone than cortical bone .Fluoride poisoning leads to severe pain
associated with rigidity and restricted movements of cervical and lumber spine,
knee and pelvic joints as well as shoulder joints . In severe cases of fluorosis,
there is complete rigidity of the joints resulting in stiff spine described as
“bamboo spine”, and immobile knee, pelvic and shoulder joints. Crippling
deformity is associated with rigidity of joints and includes kyphosis, scoliosis, and
flexion deformity of knee joints, paraplegia and quadriplegia. Skeletal fluorosis is
an irreversible process as the dental fluorosis.
The symptoms of skeletal fluorosis are as given below:
1. Severe Pain in neck, back bone or joints.
2. Stiffness in the neck.
3. Rigidity in the hip region (pelvic girdle).
4. Construction of vertebral canal and inter vertebral forearm exerts pressure
on nerves and blood vessels leading to paralysis and pain. The symptoms
of dental and skeletal Fluorosis can easily view by following photographs:
Introduction
Page | 19
1.8.3 Non – skeletal fluorosis:
This kind of fluorosis is often overlooked due to misconception that
fluoride affects only bone and teeth. Fluoride when consumed in excess can cause
several other kinds of manifestations;
Neurological: Nervousness, depression, tingling sensation of fingers and toes,
excessive thirst and tendency to urinate more frequently.
Muscular: Muscle weakness, stiffness, pain in muscles and loss of muscle power.
Allergic: Very painful skin rashes, which are perivascular inflammation prevalent
in women and children, pinkish red or non- persistent oval shaped bluish - red
spots on the skin.
Gastro-intestinal: Acute abdominal pain, diarrhea, constipation, blood in stool
tenderness in stomach.
Urinary tract: Urine may be less in volume, red in colour and passed with
itching and sensation.
Higher concentration of Fluoride can also damage a fetus, and adversely affect the
IQ of children.
Introduction
Page | 20
Table -1:3 Effects of fluoride concentration on human health
Concentration of
fluoride
Medium Effects
1 ppm Water Dental caries reduction
2ppm or < 2ppm
8ppm
Water
Water
Mottled enamel
(dental fluorosis)
10% osteosclerosis
20-80mg/day Water or food Crippling skeletal fluorosis
50ppm Water or food Thyroid changes
100ppm Water or food Growth retardation
125ppm Water or food Kidney changes
2.5-5.0ppm Acute dose Death
1.8.4 Drug induced fluorosis:
The prolonged use of drugs containing sodium fluoride is known to cause
skeletal fluorosis. During 1982, two cases of drug induced skeletal fluorosis were
reported from Switzerland. Patients of rheumatoid arthritis received uninterrupted
and prolonged treatment with niflumic acid. The daily dose of drug administered
was 3 capsules of 250 mg niflumic acid (Nifluril, UPSA Laboratories, France).
Fluoridated toothpastes and mouth rinses recommended for mouth hygiene
may cause drug induced fluorosis, particularly if the user is exposed to high
fluoride water consumption. The blood vessels in the oral mucosa and the
sublingual blood vessel absorb fluoride from these preparations. The commercial
mouth rinses are generally fluoridated preparations with very high fluoride
content.
Introduction
Page | 21
1.8.5 Industrial fluorosis:
Industrial fluorosis is a serious problem in the developed western and
other industrialized countries. However, due to rapid industrialization in India, the
problem of industrial fluorosis is reaching an alarming state and is compounding
the problem of endemic, water and food borne fluorosis (Anurag Tewari and
Ashutosh Dubey, 2009).
A number of industries use hydrofluoric acid and fluoride containing salts,
in the different sections of an industry for one reason or other. The industries that
use fluoride are-
1) Aluminum 2) Steel 3) Enamel 4) Pottery 5) Glass 6) Bricks 7)
Phosphate Fertilizer 8) Welding 9) Refrigeration 10) Rust Removal 11) Oil
Refinery 12) Plastic 13) Pharmaceutical 14) Tooth paste 15) Chemical Industries
16) Automobile Industry etc. Fluoride dust and fumes pollute the environment;
inhaling the dust and fumes is as dangerous as consuming fluoride containing
food, water or drugs.
1.9 Preventing fluoride poisoning
Fluoride poisoning can be prevented or minimized by using alternative
water sources, by removing excessive fluoride from drinking water, and by
improving the nutritional status of populations at risk.
Alternative water sources
Alternative water sources include surface water, rainwater, and low-
fluoride groundwater.
Surface water: Particular caution is required when opting for surface water, since
it is often heavily contaminated with biological and chemical pollutants. Surface
Introduction
Page | 22
water should not be used for drinking without treatment and disinfection. Many
water treatment technologies are available, but the most effective are usually too
expensive and complex for application in poor communities. Simple and low-cost
technologies, such as sand filtration, ultraviolet water disinfection or chlorine
water disinfection, are adequate in some but not all cases. Community capacity is
an essential factor in ensuring successful utilization of these technologies. Water
chlorination at household level is widely used only in emergencies.
Rainwater: Rainwater is usually a much cleaner water source and may provide a
low-cost simple solution. The problem, however, is limited storage capacity in
communities or households. Large storage reservoirs are needed because annual
rainfall is extremely uneven in tropical and subtropical regions. Such reservoirs
are expensive to build and require large amounts of space.
Low-fluoride groundwater: Fluoride content can vary greatly in wells in the
same area, depending on the geological structure of the aquifer and the depth at
which water is drawn. Deepening tube wells or sinking new wells in another site
may solve the problem. The fact that fluoride is unevenly distributed in
groundwater, both vertically and horizontally, means that every well has to be
tested individually for fluoride in areas endemic for fluorosis: extrapolating
sample tubewell tests to a larger area does not provide an accurate picture.
Changing the Dietary Habits: People living in high fluoride zone can make
certain changes in their diet, it may help them to keep away the problem of
fluorosis. Vitamin C inhibits the progress of fluorosis (P. Singh et.al. 2011).Thus
people should be directed to add items like amla, lemon, oranges, tomato,
sprouted cereals/pulses and dhainya leaves in their food. Clinical data indicate
that adequate calcium intake is clearly associated with a reduced risk of dental
fluorosis. So it is recommended to consume calcium rich food in endemic zones.
Introduction
Page | 23
It includes milk, yoghurt, leafy vegetables, drumstick leaves and sesame seed.
Foods containing anti-oxidants help in preventing fluorosis. These foods include
garlic, ginger, carrot, papaya, pumpkin white onion and green leafy vegetables.
Vitamin E also has a prophylactic role. Its sources include whole grain cereals,
vegetable oils, green vegetables and dried beans. Avoid the use of Tobacco and
beetle nut.
These do not remove Fluoride:
Boiling Water: This will concentrate the fluoride rather than reduce it.
Freezing Water: Freezing water does not affect the concentration of fluoride.
Steps to reduce Fluoride:
� Avoid fluoride supplements
Fluoride Rich Food Substances:
� Black tea and Lemon tea (tea with milk is safe)
� Black rock salt (kala namak)
� Black rock salt lased pickles
� Garam masala, salty snacks
� Chaat and Chaat masala
� Canned fruit juices
� Cannel fish
� Fluoride contaminated drinking water
� Chewing of tobacco
� Supari (arccanut) and
� Hajmola and other Churan containing rock salt
Introduction
Page | 24
Fluoride Rich Dental Products:
� Fluoridated toothpaste
� Mouth rinse
� Varnish and
� Sodium fluoride tablets(for treatment of Osteoporosis) (UNICEF)
1.10 Common defluoridation methods of drinking water:
Defluoridation means the removal of excess fluoride from water.
Defluoridation of drinking water has to been practiced by two options:-
(i) The central treatment of water at the source and
(ii) The treatment of water at the point of use that is, at the household
level.
In developed countries treatment at the source is the method adopted.
Defluoridation is carried out on a large scale under the supervision of skilled
personnel, usually at a treatment works alongside other treatment processes. Cost
is not then a limiting factor. The same approach may not be feasible in less
developed countries, especially in rural areas, where settlements are scattered.
Treatment may only be possible at a decentralized level, i.e. at the community,
village or household level. Treatment at the point of use has several advantages
over treatment at community level. Costs are lower, as defluoridation can be
restricted to the demand for cooking and drinking – usually less than 25% of the
total water demand. Chemical treatment of the entire water demand would lead to
production of large volumes of sludge, which requires a safe disposal.
It has been found that the removal of fluoride from potable water is not
adequate when initial concentration of fluoride in the water is very high and the
Introduction
Page | 25
pH of the untreated water is alkaline. Moreover, different degrees of hardness of
water require different concentrations of alum.
Limitations of point of use treatment are that reliability of the treatment
units has to be assured, and that all users should be motivated to use only the
treated water for drinking and cooking when untreated water is also available in
the house
The National Environment Engineering Research Institute in Nagpur,
India (NEERI) has evolved an economical and simple method of defluoridation,
which is referred to as the Nalgonda technique. The Nalgonda technique has been
repeatedly proven to be an economical and effective household defluoridation
technique. In this commonly used technique, fluoride is precipitated using 500
mg/L of alum and 30 mg/L of lime.
UNICEF has worked closely with the Government and other partners in
defluoridation programmes in India, where excessive fluoride has been known for
many years to exist in groundwater. In the 1980s, UNICEF supported the
Government's Technology Mission in the effort to identify and address the
fluoride problem: the Government subsequently launched a massive programme,
still under way, to provide fluoride-safe water in all the areas affected.
Defluoridation methods can be broadly divided into three categories
according to the main removal mechanism:
• Chemical additive methods
• Contact precipitation
• Adsorption/ion exchange methods
Introduction
Page | 26
Chemical additive methods
These methods involve the addition of soluble chemicals to the water.
Fluoride is removed either by precipitation, co-precipitation, or adsorption onto
the formed precipitate. Chemicals include lime used alone or with magnesium or
aluminum salts along with coagulant aids. Treatment with lime and magnesium
makes the water unsuitable for drinking because of the high pH after treatment.
The use of alum and a small amount of lime has been extensively studied for
defluoridation of drinking water.
The method popularly known as the Nalgonda technique (RENDWM,
1993), is one of example named after the town in India where it was first used at
water works level. It involves adding lime (5% of alum), bleaching powder
(optional) and alum (Al2(SO4)3.18H2O) in sequence to the water, followed by
coagulation, sedimentation and filtration (L.Iyenger,2005). A much larger dose of
alum is required for fluoride removal (150 mg/mg F-), compared with the doses
used in routine water treatment. As hydrolysis of alum to aluminum hydroxide
releases H+ ions, lime is added to maintain the neutral pH in the treated water.
Excess lime is used to hasten sludge settling. The dose of alum and lime to be
added in raw water with different fluoride concentrations and alkalinity levels
(G.Karthikeyan and A. Shunmuga Sundarraj, 1999).
The reaction occurs through the following equations:
2 Al2 (SO4)3.18H2O + NaF + 9Na2CO3 → [5Al (OH) 3 Al (OH) 2F] +
9Na2SO4+NaHCO3 + 8 CO2 + 45 H2O
3 Al2 (SO4)3.18H2O + NaF +17NaHCO3 → [5Al (OH) 3 Al (OH) 2F] + 9Na2SO4+
17 CO2 + 18 H2O
Introduction
Page | 27
The Nalgonda technique has been successfully used at both individual and
community levels in India and other developing countries like China and
Tanzania. Domestic defluoridation units are designed for the treatment of 40 liters
of water. Whereas the fill-and-draw defluoridation plant can be used for small
communities. Alum treatment is seldom used for defluoridation of drinking water
in developed countries.
Contact Precipitation
Contact precipitation is a technique in which fluoride is removed from
water through the addition of calcium and phosphate compounds. The presence of
a saturated bone charcoal medium acts as a catalyst for the precipitation of
fluoride either as CaF2, and/or fluorapatite. Tests at community level in Tanzania
have shown promising results of high efficiency. Reliability, good water quality
and low cost are reported advantages of this method (Chilton, et al., 1999).
Adsorption/ion-exchange method
In the adsorption method, raw water is passed through a bed containing
defluoridating material. The material retains fluoride either by physical, chemical
or ion exchange mechanisms. The adsorbent gets saturated after a period of
operation and requires regeneration.
A wide range of materials has been tried for fluoride uptake. Bauxite,
magnetite, kaolinite, serpentine, various types of clays and red mud are some of
the naturally occurring materials studied. The general mechanism of fluoride
uptake by these materials is the exchange of metal lattice hydroxyl or other
anionic groups with fluoride.
Introduction
Page | 28
Fluoride uptake capacity can be increased by certain pre-treatments like
acid washing, calcinations, etc. None of the mentioned materials generally
exhibits high fluoride uptake capacities.
Processed materials like activated alumina, activated carbon, bone char,
defluoron-2(sulphonated coal) used for defluoridation of drinking water .And
synthetic materials like ion exchange resins also have been extensively evaluated
for defluoridation. Among these materials, bone char, activated alumina and
calcined clays have been successfully used in the field; (Cummins, 1985,
Susannae Rajchagool and Chaiyan Rajchagool, 1997, and Priyanta and
Padamasiri, 1996).
Application of these materials is described below:
Bone Char Method: Bone char consists of ground animal bones that have been
charred to remove all organic matter. Major components of bone charcoal are
calcium phosphate, calcium carbonate and activated carbon. The fluoride removal
mechanism involves the replacement of carbonate of bone char by fluoride ion.
The method of preparation of bone charcoal is crucial for its fluoride uptake
capacity and the treated water quality. Poor quality bone char can impart bad taste
and odour to water. Exhausted bone char is regenerated using caustic soda. Since
acid dissolves bone char, extreme care has to be taken for neutralizing caustic
soda. Presence of arsenic in water interferes with fluoride removal.
In the USA in the past, a few defluoridation plants were using bone char.
Now they have been largely replaced by activated alumina. Bone char is
considered as an appropriate defluoridating material in some developing
countries. The ICOH domestic defluoridator was developed in Thailand and uses
crushed charcoal and bone char. Its defluoridation efficiency depends on the
Introduction
Page | 29
fluoride concentration in raw water as well as the fluoride uptake capacity and the
amount of bone char used in the filter. Field trials in Thailand, Sri Lanka and
some African countries have shown very encouraging results (Priyanta and
Padamasiri, 1996; Mjengera et al., 1997; and Susannae Rajchagool and Chaiyan
Rajchagool, 1997). Reports from Sri Lanka have shown that with 300 gm
charcoal (mainly to remove colour and odour) and 1 kg bone char an ICOH filter
can defluoridate on an average 450 liters of water containing 5 mg/l F- at a flow
rate of 4 liters per hour. Regeneration of spent bone char is not recommended for
these household units. Instead it should be replaced with fresh material
commercially available in local shops.
Activated Alumina Method: Aluminium oxide (Al2O3) is called Activated
alumina (or calcined alumina) .It is prepared by low temperature dehydration
(300-600°C) of aluminium hydroxides. Activated alumina has been used for
defluoridation of drinking water since 1934, just after excess fluoride in water
was identified as the cause of fluorosis.
The fluoride uptake capacity of activated alumina depends on the specific
grade of activated alumina, the particle size and the water chemistry (pH,
alkalinity and fluoride concentrations). In large community plants the pH of the
raw water is brought down to 5.5before defluoridation, as this pH has been found
to be optimum and it eliminates bicarbonate interference. The mechanism of
fluoride removal is most probably the legend exchange reaction at the surface of
activated alumina. Exhausted activated alumina has to be regenerated using
caustic soda. To restore the fluoride removal capacity, basic alumina is acidified
by bringing it into contact with an excess of dilute acid (Clifford, 1990).
Activated alumina has been the method of choice for defluoridation of
drinking water in developed countries. Generally it is implemented on a large
Introduction
Page | 30
scale in point of source community plants. A few points of use defluoridation
units have been developed which can be directly attached to the tap. During recent
years this technology is gaining wide attention even in developing countries.
Domestic defluoridation units have been developed in India using indigenously
manufactured activated alumina, which is commercially available in bulk
quantities. Choosing the proper grade of activated alumina is important for its
effective reuse in multiple defluoridation cycles. Around 500-1500 liters of safe
water could be produced with 3 kg of activated alumina when the raw water
fluoride is 11 and 4 mg/l respectively at natural water pH of 7.8-8.2. The
frequency of regeneration is once in 1.5-3 months. The cost of activated alumina
is around US$ 2 per kg and the total cost of the domestic filter depends upon
material used for filter assembly. Regeneration of exhausted activated alumina
costs around US$ 0.5 (Venkobachar et al., 1997).
Major requirements are the creation of demand for treatment and the
setting up of good supply and financing systems and arrangements for
regeneration. Sale of the ingredients and the provision of education and
monitoring through visits to user households has in some places become a source
of income for trained women promoters. The units are being evaluated in several
villages in India. Daily operational care for using these units is normally
negligible. However, the exhausted activated alumina has to be regenerated once
every few months. This is carried out at the village level.
Calcined clay Method: Freshly fired brick pieces are used in Sri Lanka for the
removal of fluoride in domestic defluoridation units. The brick bed in the unit is
layered on the top with charred coconut shells and pebbles. Water is passed
through the unit in an up flow mode. The performance of domestic units has been
evaluated in rural areas of Sri Lanka (Priyanta & Padamasiri 1997). It is reported
that efficiency depends on the quality of the freshly burnt bricks. The unit could
Introduction
Page | 31
be used for 25-40 days, when withdrawal of Defluoridated water per day was
around 8 liters and raw water fluoride concentration was 5 mg/l. As PVC pipes
are costly, a defluoridator made out of cement and bricks have also been
recommended. Apart from the methods discussed above, specific synthetic ion
exchangers and separation technologies such as reverse osmosis and
electrodialysis have also been developed for fluoride removal from potable water.
To select a suitable defluoridation method for application in developing countries,
some of the following criteria need to be considered:
• Fluoride removal capacity
• Simple design
• Easy availability of required materials and chemicals
• Acceptability of the method by users with respect to taste and cost
Both precipitation and adsorption methods have advantages and
limitations. In the Nalgonda technique easily available chemicals are used and the
method is economically attractive. Limitations of the method are varying alum
doses depending on fluoride levels in water, daily addition of chemicals and
stirring for 10-15 min, which many users may find difficult. In adsorption-based
methods like activated alumina and bone char, daily operation is negligible.
Activated alumina is costly. Hence exhausted alumina has to be regenerated using
caustic soda and acid and repeatedly reused, at least for a few cycles. Improperly
prepared bone char imparts taste and odour to the treated water. Since bone char
from point of use units is not generally regenerated, a ready supply of properly
prepared material needs to be available. Furthermore, bone char may not be
culturally acceptable to certain communities as defluoridating material.
Introduction
Page | 32
Brick powder: Defluoridation of groundwater using brick powder as an
adsorbent was studied in batch process. Different parameters of adsorption, viz.
effect of pH, effect of dose and contact time were selected and optimized for the
study. Feasible optimum conditions were applied to two groundwater samples of
high fluoride concentration to study the suitability of adsorbent in field
conditions. Comparison of adsorption by brick powder was made with adsorption
by commercially available activated charcoal. In the optimum condition of pH
and dose of adsorbents, the percentage defluoridation from synthetic sample,
increased from 29.8 to 54.4% for brick powder and from 47.6 to 80.4% for
commercially available activated charcoal with increasing the contact time
starting from 15 to 120 min. Fluoride removal was found to be 48.73 and 56.4%
from groundwater samples having 3.14 and 1.21 mg l−1 fluoride, respectively,
under the optimized conditions. Presence of other ions in samples did not
significantly affect the defluoridation efficiency of brick powder. The optimum
pH range for brick powder was found to be 6.0–8.0 and adsorption equilibrium
was found to be 60 min. These conditions make it very suitable for use in drinking
water treatment. Defluoridation capacity of brick powder can be explained on the
basis of the chemical interaction of fluoride with the metal oxides under suitable
pH conditions. The adsorption process was found to follow first order rate
mechanism as well as Freundlich isotherm.
Fired clay chips have a tendency to bind fluorides and are easily available in
village communities, thereby making it a proper choice for fluoride adsorption.
Fired clay chips are reported to have good fluoride removal capacity (Moges et
al.1996). The maximum capacity of the adsorbent was found to be 0.2 mg F- / g
of the adsorbent. 5 – 20 mg/L of fluoride solution can be reduced to less than 1.5
mg/L by using fired clay chips. One of the disadvantages of this process is that the
contact time required for the completion of the process is very high (150 hours).In
Introduction
Page | 33
conclusion, members were not very sanguine about the efficacy of groundwater
recharge on mitigating fluoride; they emphasized collection and storage of
rainwater as a safe alternative for drinking water. Fired clay chips are reported to
have good fluoride removal capacity (Moges et al.1996). The maximum capacity
of the adsorbent was found to be 0.2 mg F- / g of the adsorbent. Studies show that
5 – 20 mg/L of fluoride solution can be reduced to less than 1.5 mg/L using fired
clay chips.
Fly ash Method:
Fly ash is a major solid waste by–product of coal fired power plants. It is
produced as a fine residue carried off with the flue gases and deposited in the
electrostatic precipitator. The particle size of fly ash ranges from 10 microns to a
few mm (Agarwal et al. 2003). The main components of fly ash are silica,
alumina, iron oxides, calcium oxide and residual carbon (Yadawa et al. 1989).
The presence of unburnt carbon and surface area of 1 m2 g -1, make it a good
candidate for utilization as an inexpensive adsorbent. Sieve analysis of the fly ash
showed that the size range of the particles was between 10 – 80 µm. Adsorption
studies were conducted at room temperature in a batch process with 25 g of fly
ash and 1 L of sample solution containing known concentration of fluoride (CF).
The fly ash in a beaker is mixed with 1L of sample solution and then kept idle.
Samples were withdrawn periodically from the beaker for estimating the value of
CF.
The variation of CF found with time the fluoride adsorption ability of fly
ash is higher at higher concentration levels. This remarkable property can be
explained by the fact that at higher concentrations the less accessible sites of the
adsorbents are more likely to adsorb fluoride. The adsorption capacity of fly ash is
much higher (3.5 mg F/ g fly ash) than the other adsorbents. This may be because
Introduction
Page | 34
of the presence of unburnt carbon particles in the fly ash which are known to be
very efficient adsorbing materials (Pranab Kumar Rakshit, 2004).
Red Mud Method:
Red Mud is a very fine material (particle size of which is generally below
75µ) and high specific surface area (around 10 m2/gm) which is produced during
the Bayer process for alumina production (Hind et al., 1999). It is the insoluble
product after bauxite digestion with sodium hydroxide at elevated temperature
and pressure. It is mainly composed of iron oxides and has a variety of elements
and mineralogical phases. The removal of fluoride from aqueous solution by
using the original and activated red mud forms has been studied by many
researchers (Lopez et al., 1998). The fluoride adsorption capacity of activated
form has been found to be higher than that of the original form. The adsorption is
highly dependant on pH. Researches have revealed that the maximum adsorption
of fluoride is at pH 5.5.For pH greater than 5.5 fluoride removal decreases
sharply. It was found that the sufficient time for adsorption equilibrium of
fluoride ions is 2 h. The possibility of removal of fluoride ion by using red mud is
explained on the basis of the chemical nature and specific interaction with metal
oxide surfaces (Yunus et a1. 2002).
Red and cleaned mud was used for batch experiments. In this experiments
mud (100 g) was washed with water and taken in a plastic beaker. One liter of a
solution containing a known concentration of fluoride (CF) was added to it. The
mixture is kept undisturbed during the course of experiment. A sample was
periodically taken out of the beaker and analyzed using the fluoride – ion
selective electrode.
Introduction
Page | 35
The variation of the fluoride concentration in the water (CF) adsorbed
with time. It was observed that the amount of fluoride adsorbed increases with
time up to 140 hours after which equilibrium is attained. The capacity of mud in
contact with 1 mg/L solution of fluoride in water is 0.01 mg F / g mud. The extent
of adsorption of anions by mud is a function of the pH of the system. The
adsorption is highly dependent on PH. It reveals that the maximum adsorption of
fluoride is for PH = 4.5 to 5.For PH greater than 5.5 fluoride removal decreases
sharply (B.K. Shrivastava 2009).
1.11 Area of work: Sitapura Industrial area, Tehsil Sanganer, District Jaipur
(Rajasthan).
Sitapura Industrial Area is located 6.0 Km from Jaipur Air port along NH-
12. This area is known as EPIP (Export Promotion Industrial Park). Jaipur city is
18 km from EPIP. The area is around 365.00 acres. EPIP is located in a rural-
urban setting where greenery is profuse and fresh air in plenty. The water quality
is potable in this area. Water availability by tube wells. The Depth of tube wells
are approximate 30m. Average discharge of water is 2,000 gallons per hour. The
prominent industries of in this area are chemical and automobile industries.
Thousands of residential flats are available in and around area. ITI, Polytechnics,
Engineering Institutes, Medical Institutes and Hospitals, Management, IT and
Architectural colleges, Fashion Designing Institutes .shopping complex etc. are
located in this area.
Introduction
Page | 37
1.12 Aim of work: Due to proved health hazards, complicated procedure and
expenditure, many popular defluoridation process like - Nalgonda, Activated
alumina etc. methods are in the phase out process therefore the aim of the present
research work is to find out a best defluoridation method which is easy to use by
illiterate villagers, requires minimal expenditure, involvement of less technical
personal and effective methods for fluoride removal from drinking water so that
these methods can be apply easily every where.
1.13 Importance of defluoridation: Due to various health impacts of fluoride on
human beings the treatment of fluoride is necessary.