Innovative idea
M.Meyyappan
Ingenious design of a device for the industrial
effluent treatment with solar energy
There are many popular methods for purifying waste water from
industries and salt water from sea by using solar energy. In general all these
processes are based on boiling the contaminated water to produce steam and
condensing the steam with cool surface. It is not only the oldest but also most
effective, since it removes bacteria far below the acceptable level, but it is
inefficient in eliminating the chemical toxins there in particularly with low
boiling point. However complete sterilization of water is not required. Solutes
not dissolved in water , contaminates of high boiling point will remain in the
boiling water itself. In general 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 cheap materials. No
complicated technical knowledge is required so that it can be well used by all kind of people
even uneducated. One of the major advantages of this method is it has low
impact on the environment. It does not require any fire-wood or electricity for
heating and it is well suitable to all countries where solar flux is
available almost through the year. It
helps to solve the problem of energy crisis by saving the energy used for water
purification and water crisis by distributing drinking water to all.
An ingenious device for the industrial effluent treatment
with solar energy is designed. It is based on the vaporization at reduced
pressure. The rate of vapourization can
be increased without heating by reducing the pressure lower than the normal
atmospheric pressure. This is because lower the applied pressure , lower will
be the boiling point. The normal boiling point of pure water is 1000C
at NTP. Its boiling point decrease exponentially with the reduction in the
applied pressure. When the applied pressure is reduced by half water boils at
810C and at one fourth of the atmospheric pressure it is 520C.
Since the distillation is carried out at lower temperature, it is suitable only
for effluent with contaminate of high boiling point.
It works under the same principle as that of the 20 lts
mineral water can used for tapping drinking water in homes. It has two cans
instead of one and are connected together with a slantwise bent tube made up of
glass. Initially the bent tube is completely filled with pure water and kept
inverted by holding water inside. It is carefully placed such that one end of
which is kept immersed in the wider metallic vessel containing salt or contaminated water while the other end of
the tube is kept immersed in the pure
water taken in a glass jar with an outlet. The narrow neck will not allow fast
drainage of water and a column of water will stand in both the limbs of the
bent tube. A pressure lower than the atmospheric pressure is developed in the
bent tube above the water level. It promotes the process of vaporization. The as the boiling point is lowered due to low
pressure..The wider bottom of the tube
helps the heated water to flow into the bend glass tube effectively. The
metallic vessel is properly housed in a flat plate collector exclusively
designed for it so that solar heat collected is transferred to water by
conduction Care must be taken to reduce the energy loss by convection and
radiation from the system. The outer surface at the bottom of metallic vessel is
also blackened to absorb the solar flux directly to improve its efficiency.
With the help of a reservoir with an outlet attached with the metallic vessel waste water
is fed to the system for continuous
working. This system is best useful for waste water having contaminates of high
boiling point. During continuous usage residue will be deposited at the bottom of the
vessel which must be removed then and there, otherwise the heat conduction from
the flat plate collector will be reduced gradually.
Dr.M.Meyappan
is a retired professor of Physics worked in Alagappa Government Arts College,
Karaikudi, Tamilnadu.
