Chlorine Dosage Reduction with Ozone

Chlorine Dosage Reduction

High chlorine dosing in water can lead to the formation of trihalomethanes (THM) and haloacetic acids. These compounds, known as disinfection byproducts, are restricted in drinking water systems by the EPA to micro gram levels. THM are formed when chlorine reacts with natural organic matter (NOM) or synthetic organic matter in water.

One way to reduce the formation of THM is to replace some of the chlorine used to treat the drinking water with ozone. Both ozone and chlorine can serve as both oxidizing agents as well as disinfecting agents. In drinking water treatment ozone and chlorine are used for both purposes.

An oxidizing agent can be used to remove organic taste and odor compounds, iron and manganese, color and hydrogen sulfide. Ozone has been proven to perform these tasks. Unlike chlorine, it does not produce chlorinated byproducts such as THM or HAA. So substituting ozone for chlorine in a preoxidation process will reduce the amount of chlorine employed as well as lowering the THM and HAA levels.

Ozone is also a powerful disinfectant for water borne pathogen. In the case of certain organisms ozone is a much better disinfectant than chlorine. Ozone can be used as a primary disinfectant since it is short lived and can't leave a residual in the distribution system. The primary disinfectant inactivates the pathogens in the water while the secondary disinfectant keeps the pathogens from returning and provides a simple method of measuring the safety of the water. By using ozone as the primary disinfectant and chlorine as the secondary disinfectant, the amount of chlorine used is significantly reduced, further limiting the formation of THM and HAA.

Combining ozone and chlorine for drinking water treatment improves water quality while still maintaining the down stream benefits of chlorine in the water distribution system.