Ozone has been shown to be effective in a variety of drinking water applications including: disinfection, color removal, iron (Fe) and manganese (Mn) reduction, hydrogen sulphide removal, taste and odor reduction micro pollutant removal and improved filtration and flocculation of potable water. Ozone can also reduce formation of disinfection by-products such as trihalomethanes and haloacetic acids. Ozonation is effective for removal of difficult-to-treat pathogens such as giardia and cryptosporidium.
Municipal water contains a lot of bacteria and other microorganisms. Chlorine has been the only general disinfectant used in treating this water for disinfection so far. This has changed in the last two decades as almost all the municipal water treatment plants have gone in for ozone as the primary disinfectant. While chlorine produces carcinogenic chloro by-products, these are consumed while drinking this water. Hence ozone is used for primary disinfection to take care of the disinfection in the primary stage. However, the drawback for ozone in this particular case is its very short half life. As a result, there is no ozone in water when received at the consumer end. While the water is being transported, since there is no residual disinfectant in water, the bacteria will breed again. For this reason alone, some amount of chlorine is required to maintain the required residual disinfectant in water to take care of the bacteria during the long transit time till it reaches the consumer. Since the primary disinfection load is taken over by ozone, the requirement of chlorine for only maintaining the residual disinfectant in water is quite little. As a result the quantity of harmful chlorine by-products is reduced and so is the risk associated with it. This is the primary advantage of using chlorine for this usage.
The application of ozone in municipal water treatment is quite simple. After the water is pumped from the source, it undergoes various stages of treatment to reduce the colloidal and suspended particles. Ozone is applied to this water, again using injector or diffusers inside a large contact tank to inject and to dissolve ozone in the water. Sufficient time is given in the contact tank to carry out the disinfection and oxidation reactions. Required quantity of chlorine is injected in to the water after ozonation and it is taken to the pump house to pump to the township localities to the end consumers.