Trihalomethanes (THMs) are a group of chemical compounds that can form when chlorine or other disinfectants react with organic matter in water. They are named for their chemical structure, which includes three halogen atoms (such as chlorine, bromine, or iodine) bound to a single carbon atom.

The most common THMs found in water supplies include chloroform (CHCl3), bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl), and bromoform (CHBr3). These compounds are considered disinfection byproducts (DBPs) because they are created as a result of the disinfection process used to kill harmful microorganisms in drinking water.

THMs are regulated in drinking water because they have been associated with potential health risks. Long-term exposure to high levels of THMs has been linked to an increased risk of certain cancers, as well as adverse reproductive outcomes.

The Maximum Contaminant Level (MCL) for Total Trihalomethanes (TTHMs) in drinking water, as set by the United States Environmental Protection Agency (EPA), is 0.080 milligrams per liter (mg/L) or 80 micrograms per liter (µg/L).

Trihalomethanes (THMs) are formed as disinfection byproducts (DBPs) when chlorine and/or bromide react with naturally occurring organic and inorganic matter present in water. The formation of THMs typically occurs during the disinfection treatment process at the treatment plant and THMs continue to formed in the distribution system as water age in the system.

The rate of THM formation is influenced by water temperature and concentration of free chlorine residual in the water. Highest THM levels are typically found at the far-end of the distribution system where water age is high.

Aeration is a water treatment process that involves exposing water to air, typically by bubbling air through the water or allowing water to come into contact with air. Aeration can remove certain volatile organic compounds (VOCs), including some trihalomethanes (THMs), from water through a process known as air stripping. The THMs dissolved in the water have a tendency to volatilize into the air because they are relatively volatile compounds.

Halo Acetic Acids (HAAs) are disinfection byproducts (DBPs) that form when chlorine or other disinfectants react with natural organic matter in water. HAAs are not volatile, therefore aeration is not an effective method for directly removing them from water.

Henry's Law is a principle in physical chemistry that describes the relationship between the concentration of a gas in a liquid and the partial pressure of that gas above the liquid. It states that at a constant temperature, the amount of gas dissolved in a given volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with the liquid.

In-tank aeration refers to an aeration process deployed inside a water storage tank in drinking water distribution system. It is generally a combination of active mixing, active ventilation and surface aeration equipment.

The PAX THM Removal System (PAX TRS™) is a technology using in-tank aeration to remove THMs from drinking water. Each system is designed and sized to remove THM in under to achieve a desired percentage removal (%) of THM.

Active ventilation is critical to remove volatile such as THMs into a drinking water storage tank. Without sufficient air-exchange between the head space inside of the tank and the air outside, the air inside the tank becomes saturated with THMs and the mass transfer stopped because the equilibrium described by Henry’s law is reached.

Several factors influence the THM removal for a specific project. The main factor is the amount of water to treat, and the amount of aeration energy/equipment used.

In practice, PAX TRS™ solutions are designed and sized given a maximum turnover rate and removal requirements. Once installed, the performance of aeration will depends on the amount of water to be treated each day.

Yes, aeration can remove free chlorine from water but typically not significantly.

Free chlorine exists as a combination of hypochlorous acid (HOCl), which is somewhat volatile, and hypochlorite ions (OCl⁻), which are non-volatile. The pH of the water affects the relative concentrations of HOCl and OCl⁻. At typical drinking water pH levels, OCl⁻ predominates, which is why aeration doesn't significantly affect chlorine residual.

There exist several strategies to reduce THMs:

• Removing organic matter, which serves as a precursor, at the treatment plant.
• Decreasing the disinfection dosage applied.
• Employing aeration to eliminate THMs post-formation.
• Adopting alternative disinfection methods like chloramine.