Fundamentals of prevention and control of air pollution:
As mentioned in my earlier discussion, air pollutants can be gaseous or particulate matters. Different techniques for controlling these pollutants are discussed below:
A. Methods of controlling gaseous pollutants -
1. Combustion - This technique is used when the pollutants are in the form of organic gases or vapors. During flame combustion or catalytic process, these organic pollutants are converted into water vapor and relatively less harmful products, such as CO2.
2. Absorption - In this technique, the gaseous effluents are passed through scrubbers or absorbers. These contain a suitable liquid absorbent, which removes or modifies one or more of the pollutants present in the gaseous effluents.
3. Adsorption - The gaseous effluents are passed through porous solid adsorbents kept in suitable containers. The organic and inorganic constituents of the effluent gases are trapped at the interface of the solid adsorbent by physical adsorbent.
B. Methods to control particulate emissions:
1. Mechanical devices generally work on the basis of the following:
(a) Gravity: In this process, the particles settle down by gravitational force.
(b) Sudden change in direction of the gas flow. This causes the particles to separate out due to greater momentum.
2. Fabric Filters: The gases containing dust are passed through a porous medium. These porous media may be woven or filled fabrics. The particles present in the gas are trapped and collected in the filters. The gases freed from the particles are discharged.
3. Wet Scrubbers: Wet scrubbers are used in chemical, mining and metallurgical industries to trap SO2, NH3, metal fumes, etc.
4. Electrostatic Precipitators: When a gas or an air stream containing aerosols in the form of dust, fumes or mist, is passed between two electrodes, then, the aerosol particles get precipitated on the electrode.
C. Apart from the above, following practices also help in controlling air pollution.
(i) Use of better designed equipment and smokeless fuels, hearths in industries and at home.
(ii) Automobiles should be properly maintained and adhere to recent emission-control standards.
(iii) More trees should be planted along road side and houses.
(iv) Renewable energy sources, such as wind, solar energy, ocean currents, should fulfill energy needs.
(v) Tall chimneys should be installed for vertical dispersion of pollutants.