Air stripping is a process by which a liquid, usually wastewater, is brought into intimate contact with a gas,usually air, so that some undesirable volatile substances present in the liquid phase can be released and carried away by the gas. Processes such as mechanical surface aeration, diffused aeration, spray fountains, spray or tray towers, and countercurrent packed towers are encompassed by the term air stripping. These procedures produce a condition in which a large surface area of the water to be treated is exposed to air, which promotes transfer of the contaminant from the liquid phase to the gaseous phase.