Where water is contaminated with a volatile organic chemical, air stripping is often the most cost-effective method of treatment either to lower the concentration to an acceptable value, or as pre-treatment prior to GAC adsorption. Many volatile organic chemicals are poorly adsorbed by GAC whereas they are easily removed by air stripping. Examples of chemicals that can be economically removed by air stripping include trichloroethane and tetrachloroethane. Air stripping is also used for removal of CO ₂.

The theory of air stripping does not lend itself to a simple summary. It is based on the fact that if the partial pressure of a volatile chemical is greater in a solution than in the air with which it is in contact, the chemical will move from water to air. Air stripping provides the optimum conditions necessary for the transfer to proceed. The rate of transfer depends on many factors, the most important of which are:

• the difference in vapour pressures the rate of transfer is proportional to the difference in vapour pressures which can be thought of as the driving force;

• the solubility of the volatile chemical (which is related to the Henry constant of the chemical; soluble gases have a low Henry constant);

• the surface area across which transfer takes place;

• the mixing within the liquid, bringing water with a higher concentration of pollutant in contact with air; and

• the ease with which the volatile chemical diffuses within the liquid.

Air stripping normally involves a tower filled with...