In a water treatment plant in Killaloe in the province of Ontario, Canada, chlorine was used as disinfectant for many years. However, by using chlorine, toxic by-products (trihalomethanes (THMs)) are formed when chlorine reacts with organic matter present in the water. Trihalomethanes are carcinogenic and therefore, the Ministry of the Environment (MOE) dictated that the level of THMs in drinking water should not exceed 100 μg/l.
When exceeding the legislated limit of 100 μg/l, the drinking water system was flushed and the water in the clear wells was renewed. This was an effective solution, but it was temporally and it had a couple of disadvantages. This method was inefficient, because large quantities of treated water was wasted. This method was also very costly due to the use of chemicals and electricity for waste water treatment.