Prevention and control of air pollution Health

 Prevention and control of air pollution Health
There are two types of air pollutants—gaseous and particulate.
Methods of controlling gaseous air pollutants
(i) Combustion. This technique is used for controlling those air pollutants that
are in the form of organic gases or vapours. In this technique, the organic air
pollutants are subjected to flame combustion technique (also known as catalytic
combustion). In this technique, organic pollutants are converted into less
harmful products and water vapour.
(ii) Absorption. Absorption is a process in which a substance penetrates into
another substance like scrubbers. In this technique, gaseous pollutants are
passed through absorbing material like scrubbers. These scrubbers contain a
liquid absorbent. This liquid absorbent removes the pollutants present in
gaseous effluents. Thus the air coming into scrubber is free from pollutants and
it is discharged into atmosphere.
(iii) Adsorption. Adsorption is a process in which a substance sticks to the surface
of another substance (called absorbent). In this technique, gaseous effluents are
passed through porous solid absorbent kept in containers. The gaseous
pollutants stick to the surface of the porous material and clean air passes
through. The organic and inorganic constituents of gaseous effluents are
trapped at the interface of solid adsorbent by physical adsorbent.
Methods to control particulate air pollutants
The particulate air pollutants such as dust, soot, fly ash etc. can be controlled by
using fabric filters, electrostatic precipitators, wet scrubbers and mechanical devices
etc.
(i) Fabric filters. In this technique, gaseous emission containing dust, soot and
fly ash is passed through porous fabric filters made of fabric (cloth) (woven
or filled fabric). The particles of pollutants get trapped in this fabric and are
collected in the filter and the gases free from the pollutant particles are
discharged.
(ii) Mechanical devices. There are many mechanical devices that clean the air of
pollutants either due to (i) gravity in which the particles settle down by
gravitational force; or by (ii) sudden change in the direction of gas flow in which
particles separate out due to greater momentum.
(iii) Electrostatic precipitators. In this technique, a gas or air stream containing
aerosols in the form of dust, mist or fumes, is passed between the two electrodes
of the electrostatic precipitator. During this process, the aerosol particles get
precipitated on the electrodes.