An air stripper in the form of an submerged gas evaporator or a submerged gas reactor that includes a vessel, a gas delivery tube partially disposed within the vessel to deliver a gas into the vessel and a contaminated liquid inlet that provides a contaminated liquid to the vessel at a rate sufficient to maintain a controlled constant level of process fluid within the vessel. A weir is disposed within the vessel adjacent the gas delivery tube to form a first fluid circulation path between a first weir end and a wall of the vessel and a second fluid circulation path between a second weir end and an upper end of the vessel. During operation, gas introduced through the tube mixes with the process fluid and the combined gas and fluid flow at a high rate with a high degree of turbulence along the first and second circulation paths defined around the weir, thereby promoting vigorous mixing and intimate contact between the gas and the process fluid. This turbulent flow develops a significant amount of interfacial surface area between the gas and the process fluid resulting in a reduction of the required residence time of the gas within the process fluid to achieve thermal equilibrium and/or to drive chemical reactions to completion, all of which leads to a more efficient and complete evaporation, chemical reaction, or combined evaporation and chemical reaction process.