A simple and direct method for
Desalination of salty water by solar energy with innovative design
Popular methods for purifying water
are Filtration in stages, Boiling, Distillation (De-salination of
seawater), Reverse
osmosis, In Situ Chemical Oxidation(ISCO)
. Boiling
is the oldest and most effective method since it eliminates most microbes
causing intestine
related diseases,
but it cannot remove chemical toxins or impurities. However for human
health, complete sterilization of water is not
required, since the heat resistant microbes are not intestine affecting. In
general distillation involves boiling the water to produce water vapour. The
vapour contacts a cool surface where it condenses as a liquid. Because the
solutes are not normally vapourized, they remain in the boiling solution. Even
distillation does not completely purify water, because of contaminants with
similar boiling points and droplets of unvapourised liquid carried with the
steam. However, 99.9% pure water can be obtained by distillation. Solar disinfection is a low-cost method of disinfecting water that can often be implemented with locally available materials .No complicated technical knowledge is required so that it can be well used by all kind of people even uneducated. One of the main advantages of this method is it has low impact on the environment .It does not require any fire-wood, or electricity ,and it is well suitable to country like India where solar flux is available almost throughout the year. By adopting this method by all the nationals for their requirements of water, the nation can solve both the energy crisis (by reducing the energy used for water purifications) and drinking water problem.
Distillation by solar energy at NTP will remove from water almost anything, even heavy metals, poisons, bacteria and viruses. But if it done under reduced pressure, as the process is carried out at lower temperature, the removal of such unwanted things will not be complete. A simple and very ingenious method of achieving desalination under reduced pressure is given below:
Requirements: one
cylindrical aluminium vessel (little broad) and a similar vessel made of
plastic or glass, a broad twice bend glass tube( like inverted
)
Initially the bend tube is fully filled with pure water
and kept such that one end is kept
immersed in the salty water taken in the aluminium vessel placed on the flat
plate collector and the other end is
kept immersed in the pure water taken in the glass vessel placed outside the
system.The connecting bend tube is fixed so that it is slightly inclined
towards the glass tube .It helps the condensed water to flow towards the glass
container.When the water filled bend tube is erected like this the pressure
inside the connecting tube will be less than the NTP which will help promoting
the process of vapouraization.
