When comparing disinfection efficiency, Ozone is 25 x more effective than Hypochlorous acid (HOCl), 2,500 x better than Hypochlorite (OCl) and 5,000 x more than Chloramine (NH2Cl). These results are measured from the comparison of CT constants ? the Concentration x Time needed to kill 99.99% of all micro-organisms. Chlorine reacts with organic materials to form organics containing Chlorine such as Chloroform, Carbon Tetrachloride, Chloromethane and others, generally known as Trihalomethanes (THMs).

Ozone reacts with Organics to break them down into simpler compounds. These organics (Oxalic Acid for example) do not readily break down all the way to Carbon Dioxide with just Ozone, but if subjected to bacterial degradation on activated charcoal, they will be removed. This water can be later treated with a low level of Chlorine, say 0.2-0.3 ppm, to maintain sanitation in the distribution system. This way no THMs will be formed. THMs have been implicated as carcinogens in the development of Kidney, Bladder and Colon Cancer. The regulatory authorities are again decreasing the allowable levels of THMs in Community water systems. At the present time the limit is 0.05 ppm. Based on the scientific research, the level will be most likely soon be lowered to 0.01 ppm.

Ozone does not react significantly with THMs as they are more resistant to oxidation - it takes a very long time to achieve full oxidation. Some THMs are removed as a result of physical sparging by the aeration action of the ozone/air mixture.