A fluid scrubber in the form of a submerged gas reactor includes a reaction vessel, a gas delivery lube partially disposed within the reaction vessel to deliver a gas into the reaction vessel and a scrubbing liquid inlet that provides a scrubbing liquid to the reaction vessel at a rate sufficient to maintain a controlled, constant level of fluid within the reaction vessel. A weir is disposed within the reaction vessel adjacent the gas delivery tube to form a first fluid circulation path between a first weir end and a wall of the reaction vessel and a second fluid circulation path between a second weir end and an upper end of the reaction vessel. During operation, gas introduced through the tube mixes with the scrubbing liquid and the combined gas and liquid 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 scrubbing liquid. This turbulent flow develops a significant amount of interfacial surface area between the gas and the scrubbing liquid resulting in a reduction of the required residence time of the gas within the scrubbing liquid 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.