WATER FLUORIDATION

Dr shabeel pn

Dean and co-workers in USADecreased F- caries; Increased F-Dental

fluorosisNormal F content- 1-1.5mg of fluoride/litre

INTRODUCTION

Defined as the upward adjustment of the concentration of fluoride ion in a public health water supply such a way that concentration of fluoride ion in water may be consistently maintained at one part per million by weight to prevent dental caries with minimum possibility of causing dental fluorosis.

DEFINITION

o In temperate regions – 1ppm.

Optimal fluoride concentration & climatic conditions.

Temp in degree Celsius

Recommended ppm

≤18.3 1.1 – 1.3

18.9 -26.6 0.8 – 1.0

≥26.7 0.5 -0.7

For colder climates where the mean annual maximum air temperature is lower than 10 degree celcius fluoride concentration in water as high as 1.3 ppm must be considered safe and beneficial

Irrigation water – 10 mg/l

Aquatic life - 1.5 mg/l Industrial water supply – 1.0 mg/l

Levels of fluoride used.

Before fluoridation , the following factors should be taken into account

1. Daily fluoride concentration of the water supply

2. Baseline dental caries prevalence3. Index of enamel fluorosis and post

fluoridation data of the same population.

Japanese limit their fluoride content since they eat fish which is rich in fluorides.

500 ml of water is taken in a clean dry polythene container

2cc of 6 N HCl is added to inhibit growth/enzymatic change

Store at 4 degree celsius for analysis.

Sample collection for fluoride estimation.

Fluoride concentration can be estimated by1. Fluoride electrode coupled with standard

pH meter.2. Scot- Sanchis method

Universally acceptable, quick, simple, economic.

pH meter is used in conjuction with a fluoride electrode & electrode potentials of the sample is calculated.

Two pH meters are used-Orion901 & Orion 407

Ion meter is one that has inbuilt facility of converting the electrode potentials into concentration of fluoride in ppm

Fluoride electrode coupled with standard pH meter

The unknown concentration of fluoride is calculated by

1. Typical calibration curve2. Applying electrode potential difference by

equation3. Direct ppm reading.

Scot – Sanchis method

• Based on reaction between fluoride and red zirconium alizarine lake.

• Fluoride forms a colourless complex ion-ZrF6 & liberates free alizarine sulphuric acid(yellow)

• As the amount of fluoride increases, the colour varies from yellow to red.

• Fluoride level is determined by comparing the colour with that of standards.

• No longer used.

50 percent of population in rural areas. Centralised water distribution system is

lacking.

Limitations of community water fluoridation.

Should be adapted to local conditions & needs of water network

Must be efficacious, safe &precise in all climatic conditions

Of standard type-maintenance easily provided. Choice of distributor should be based on the

quantity & type of fluoride bearing product used

Equipment should have well defined precision limits i.e not more than 5 percent error in the

Choice of equipment & chemical for water fluoridation.

Whole system whatever variation in quantity of water

It should have a safety mechanism that automatically stops the addition of fluoride if the flow through the treatment plant is suddenly reduced

Adjustment must be easy and rapid Apparatus should operate between 20 & 80

percent of total capacity

In each fluoridation system, an antisiphon mechanism should be installed in pipes distribute fluoride solution into water, to avoid a concentrated solution of fluoride entering the system.

a) Fluorspar- mineral containing varying amounts of

CaF2b) Sodium fluoride- white, odorless,free flowing material

available either as a powder or a mixture of various crystals

- expensive source of fluorides c) Silicofluoride- obtained as by product of purification of

phosphate rocks

Fluoride compounds used in water fluoridation

d)Sodium silicofluoride - Most popular - Low cost, cheapest form of fluoride - Solutions are corrosive.e)Hydrofluosilic acid - More expensivef)Ammonium silicofluoride - Produced by neutralising fluosilic

acid with either aqueous ammonia or ammonia in gaseos form

1. The saturator system2. The dry feeder system3. The solution feeder system

Types of equipment for water fluoridation

Principle – 4 percent solution of sodium fluoride is produced and injected at the desired concentration at the water distribution source with the aid of a pump.

The saturator system

Factors limiting the utilisation – a high hard water level ( total

hardness of over 75 mg/l)

Recommendation – for small town with a total

requirement of less than 3.8 million litres/ day

Principle – Sodium fluoride or silicofluoride in the form of powder is introduced into a dissolving basin with the aid of an automatic mechanism

The dry feeder

Factor limiting utilisation – the need for care of handling of

fluoride, obstruction of pipes, compacting of fluoride while stacked in humid atmosphere.

Recommendation – in medium sized town- 3.8 -19

million l/day

Principle- Volumetric pump permitting the addition of a given quantity of hydrofluosilic acid in proportion to amounts of water treated.

The solution feeder

Factors limiting utilisation – resistant to attack by

hydrofluosilic acidRecommendation – in medium and large towns Capacity more than 7.6 million/ day

These three systems incorporate electrical and mechanical devices that require maintenance by capable operators.

The Venturi fluoridator system and the saturation suspension cone are the two systems which do not suffer from these drawbacks.

Non electrical system developed by J N Leo Activated by the flow of water in the main

water line and there no possibility of accidental overdosing by surges of fluoride when the main water pump stops

The tank containing fluoride is made of clear acrylic thermoplastic(plexiglass)

Venturi fluoridator system

Simple to install Cost is only three-fourths even though same

amount of chemicals are used Non electrical system Operator can make visual inspection of the

level of chemicals

Advantages

Consists of an upside down cone charged with a bag of sodium silicofluoride through which a constant flow of water percolates

The solution is collected at the top by a horizontal perforated plastic pipe which forms the outlet

Saturation suspension cone

A cone 0.91m high and 0.91m in diameter, mounted upside down

An elevated constant head tank(7-10m head) for feeding water to prepare a constant volume of solution

A 2cm diameter connecting pipe from the constant head tank to the lower end of the cone

A surface collector consisting of a horizontal perforated 2.5 cm diameter pipe collects the solution and discharges into a wide mouth funnel which is connected to the pipe

Parts of installation

The cone must be built of a corrosion resistant material such as stainless steel or fibreglass

The cone is charged with a 45 kg bag of sodium silicofluoride

The quantity of salt in the cone be never less than 25 kg

a) Maintenance and control The fluoridation system must be

carefully maintained to ensure maximum efficiency

Uniform concentration of fluoride ions should be maintained

Technical considerations of water fluoridation

b) Control at the water treatment plans Any difference in the fluoride content

of water should be checked The analysis should be done several times

a day

c) Control of the quality of analysis• The responding authority should

send three blind samples each month for analysis at the water treatment plant which should be returned to the responsible authority within 48 hrs

• If any difference known, technical assistance should be sought

d) Control of the quality of water in the network

Personnel from the water plant should take samples from the network once a week and send them for analysis

Fluctuations in concentrations should be noted

e) Control of the quality of fluorides usedEach time the delivery of fluorides is

received, the samples should be analysed to verify whether they correspond to the criteria of quality approved by the responsible authorities.

a) Hourly check of he weight of the chemical fed into the hopper.

b) Calorimetric chemical testing through addition of zirconium alizarin reagent and the results to be compared with the standards

c) Less frequent calorimetric testing is advisable(at weekly intervals) upon water at various parts of the distribution system

d) Continuous electronic measuring and controlling of fluoride concentration in water

Monitoring of fluoridated water

To reduce the fluoride concentration to optimal level

Reduce occurrence of dental fluorosis. Avoid other adverse effects.

Partial removal of fluoride

1) At a central water treatment plant by absorption of fluoride in a suitable medium by means of an ion exchange process

2) By the use of smaller units using similar principles, installed at home and other places where drinking water is made available for children

3) By bringing of water of lower fluoride content from other sources to mix with and dilute the high fluoride water.

Achieved by

4) By providing bottled lower fluoride water separately to homes and other places where children drink water

There is municipal water supply reaching a reasonable number of homes

People drink this water rather than water from individual wells or tanks

Suitable equipment is available in a treatment plant or pumping station

A supply of a suitable fluoride chemical is assured

There are workers in the water treatment plant able to maintain the system

Practical aspects of water fluoridation

There is sufficient money available for the initial installation and running costs

But with increase in dental caries, it is urged that water fluoridation be considered soon as safe drinking water

Medical investigations shown that optimal concentration of fluoride is safe and does not impair general health

In cases of excessive fluoride intake either in areas of high concentration or in industrially polluted drinking water , secondary effects might appear in the form of dental and skeletal fluorosis.

Evaluation and safety of water fluoridation

Attained by the country of a fair level of economic development.

Availability of municipal water supplies reaching a large number of homes.

Evidence that people drink water from the municipal supply rather than from wells or tanks.

Availability of the requisite equipment needed in a treatment plant.

Availability of reliable supply of fluoride

Requirements for introducing community water fluoridation

Availability of trained workers who are able to maintain the system.

Availability of sufficient money. A level of dental caries in the community

that is high or firm indicating that caries level is increasing.

Appropriate legisation authorizing community water fluoridation

Several methods have been suggestedi. Based upon ion exchange process or

adsorption andii. Based upon addition of chemicals to water

during treatment. In India, the first work on defluoridation was

done by the National Environmental Engineering Research Institute (NEERI) at Nagpur in 1961.

Defluoridation of water

a) Defluoron 1 : A sulphonated raw dust impregnated with 2 percnt alim solution.

b) Carbion: Used on sodium and hydrogen cycles

c) Magnesia: It removed the excess fluoride but pH of treated water was beyond 10 and its correction by acidification and recarbonation was necessary.

d) Defluoron 2 : It is a sulphonated coal and works on aluminium cycles

Cation Exchange Resins

Involves addition of two readily available chemicals

Addition of sodium aluminate or lime, bleaching powder and filter alum to the fluoride water followed by flocculation, sedimentation and filtration.

Useful for domestic and community water supplies.

Nalgonda technique of defluoridation

These are stainless steel candle filters adopting Nalgonda technique

Consists of water filters of any size and make fitted with candle filters and an additional mixing device

Domestic defluoridation filters

Rapid mix: Is an operation by which the coagulant is rapidly and uniformly dispersed throughout single or multiple phase system

Helps in formation of microflocs and results in proper utilization of chemical coagulant, preventing localisation of concentration and premature formation of hydroxides.

Mechanism of defluoridation by Nalgonda technique

Flocculation: Second stage of the formation of

settable particles(flocs) from destabilised colloidal sized particles and is achieved by gentle and prolonged mixing.

Sedimentation:Separation from the water by

gravitational setting of suspended particles that are heavier than water

Factors influencing sedimentationa) Size, shape,density and nature of the

particlesb) Viscosity, density and temperature of

waterc) Surface overflow rated) Velocity of flowe) Effective depth of setting zone

FiltrationIt is a process for separating

suspended and colloidal impurities from water by passage through porous media.

Fill 22 litres of test water in the upper chamber

Add the required dose of aluminium salt solution

Mix it rapidly for a period for 30-60 seconds with a speed of 10 – 20 rpm

On chemical reaction tiny flocs are formed Then mix for a period of 10-15 min with a

speed of 2-4 rpm Water is allowed to settle and filter through

Operation and maintenance of Nalgonda technique

earth candles overnightSalient features of Nalgonda technique No regeneration of media No handling of caustic acids 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

Highly efficient removal of fluoride Little wastage of water Minimum mehanical and electrical

equipment No energy except muscle power required

Absence of acceptable,alternate low fluoride source within transportable distance

Total dissolved solids are below 1500mg/l; desalination may be necessary

Raw water fluoride ranging from 1.5mg to 20 mg F/l

Indications

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