Surface and Spray Aeration

Gas transfer in water and wastewater treatment is a process whereby water is brought into contact with air or a gas and, because of the presence of a concentration gradient, the transfer of gases to and/or from the water occurs. In water treatment, for example, aeration is used to remove carbon dioxide, hydrogen sulfide, methane, and various volatile organic compounds, and to oxidize iron and manganese in the water. In wastewater treatment, the gas transfer is used primarily in the activated sludge and trickling filtration processes and in aerated lagoons and aerobic digesters. Air or oxygen gas is supplied to the wastewater by air compressors and by mechanical aerators to induce a higher concentration gradient in the wastewater and thereby to accelerate oxygen transfer. The spray of wastewater by nozzles over trickling filter beds also results in an accelerated oxygen transfer. In polluted streams and lakes, oxygen transfer from the limitless atmosphere to the water occurs, also because of the existence of dissolved oxygen concentration (or deficit) gradient. This reaeration process is an important and essential element of the stream self-purification process.