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
Before fluoridation , the following factors should be taken into account Daily fluoride concentration of the water supply Baseline dental caries prevalence 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.
Fluoride concentration can be estimated by Fluoride electrode coupled with standard pH meter. 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 Typical calibration curve Applying electrode potential difference by equation Direct ppm reading.
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.
Fluorspar- mineral containing varying amounts of CaF2 b) 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 expensive f)Ammonium silicofluoride - Produced by neutralisingfluosilic acid with either aqueous ammonia or ammonia in gaseos form
The saturator system The dry feeder system 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 acid Recommendation – 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 Venturifluoridatorsystem and the saturation suspension cone are the two systems which do not suffer from these drawbacks.
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)
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
Any difference in the fluoride content of water should be checked
The analysis should be done several times a day
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 used
Each 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
At a central water treatment plant by absorption of fluoride in a suitable medium by means of an ion exchange process By the use of smaller units using similar principles, installed at home and other places where drinking water is made available for children 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 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 suggested Based upon ion exchange process or adsorption and 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
Defluoron 1 : A sulphonated raw dust impregnated with 2 percntalim solution. Carbion: Used on sodium and hydrogen cycles Magnesia: It removed the excess fluoride but pH of treated water was beyond 10 and its correction by acidification and recarbonation was necessary. 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.
Separation from the water by gravitational setting of suspended particles that are heavier than water
Factors influencing sedimentation Size, shape,density and nature of the particles Viscosity, density and temperature of water Surface overflow rate Velocity of flow Effective depth of setting zone
Filtration It 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 overnight Salient features of Nalgonda technique
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