In-tank aeration is the process of exposing finishing drinking water to air – any volatile chemicals that are in the water (such as disinfection byproducts) will evaporate into the air.
Trihalomethanes are formed from the reaction between natural organic matter in raw water and chlorine (Cl) disinfectant. They continue to form as water travels through distribution system and ages, especially in tanks, and are the most common regulated DBP. In-tank aeration deals with THMs where they are the highest and is very effective at removing THMs.
Chlorine and chloramine are more stable in water than THMs, and we have seen little to no loss of residual in our in-tank aeration installations. In side-by-side measurements, we measured roughly 10% reduction in residual chlorine in a system that removed 50% of TTHMs. At pH levels lower than 7, we expect a greater fraction of residual chlorine to exist in the form of hypochlorous acid, which is slightly volatile. Therefore, we generally expect more residual chlorine to be lost due to aeration in low-pH systems.
There are other benefits of in-tank aeration besides THM reduction. Mixing is an essential component of in-tank aeration – it contributes to THM reduction and helps lower any other volatile compounds in the water, such as hydrogen sulfide (H2S). Aeration can also lower carbon dioxide (CO2) levels. Some municipalities have found that pH levels rose naturally in their water due to the removal of CO2 by the aeration process and no longer needed to feed caustic soda into their system, saving roughly $5,000 a month.