Environmental Engineering Reference
In-Depth Information
Following the intervention, a further dental survey of the same 1000 children was done.
Results from the dean's survey indicate a reduction in the prevalence of grade I luorosis
by 86%, grade II luorosis by 77%, and grade III by 60%. There was a minor increase in
grade II luorosis by 21% owing to the change in the cohort age of the study group during
the 2 years. Overall, the IFM resulted in a drastic reduction in the prevalence of dental
luorosis and increased the number of healthy teeth by 154%.
17.3 Technological Options for Water Defluoridation
Although the above-described options of deluoridation can be considered as effective
and do not require user involvement, the feasibility of many of those options depend on
hydrogeological conditions, require higher initial cost, and take a long time for planning
and implementation. This led to deluoridation of drinking water as the most feasible
option in most parts of the world. In the user point of view, there could be two options
of deluoridation: (i) centralized or community-level water treatment, often at the source,
and (ii) the treatment of water at the point of use (POU), i.e., at the household level. There
are fundamental differences as well as advantages and limitations of these approaches.
The centralized approach offers excellent control over deluoridation treatment and can
be combined with regular drinking treatment processes, leaving no risk of quality control
at the POU. Accordingly, in many developed countries, treatment at source is commonly
practiced. Deluoridation treatment is carried out on a large scale under the supervision
of skilled technical personnel. The same approach may not be feasible in the rural areas of
less developed countries, where settlements are often scattered. Chemical treatment of the
entire water demand for deluoridation process also leads to generation of large amounts
of sludge/solid waste as well as wastewater. This requires safe disposal or proper treat-
ment, further adding to the cost.
On the other hand, domestic deluoridation is attractive for the reason that only 5%-20%
of the total water requirement needs to be treated, considering this small fraction is typi-
cally used for drinking and cooking purposes. This obviously makes domestic deluorida-
tion an attractive option in developing countries where the cost of treatment is a major
issue. Contradictory to this advantage, poor user awareness and implementation issues
with poor control of water quality create challenges for domestic deluoridation in rural
areas of many developing countries. Limitations of POU treatment are also related to the
reliability of treatment units, and that all users should be encouraged to use only the treated
water for drinking and cooking when untreated water is also available in the house. In
general, a centralized approach is adopted also in urban areas of developing countries, and
rural habitations appear to be the target areas for domestic deluoridation techniques.
Several methods for deluoridation of water have been developed; however, only a few
have found widespread acceptability in terms of techno-economic feasibility. Most of these
methods can be broadly categorized according to the principle of water treatment:
• Precipitation-based methods
• Membrane-based processes
• Electrochemical methods of water treatment
• Selective adsorption and ion-exchange-based methods
