Switching over from Chlorine to Chloramination

The Eastern Municipal Water District (EMWD) has traditionally treated water from its wells by injecting gaseous chlorine that was stored on site in both one-ton containers and in smaller, 150 lb cylinders. Established in 1950, EMWD served a population of about 20,000, but today the district is responsible for 440,000 residents. Concerns about safety and meeting increasingly tougher regulations prompted the district to examine alternative treatment methods. Most of the district's source water is purchased from the Metropolitan Water District (MWD); only 25%-30% of its water originates from local wells. The MWD water is chloraminated by a process that uses a five-to-one ratio of chlorine mixed with ammonia to produce chloramines, which are four times more stable than chlorine and can reduce the formation of trihalomethanes (THMs). Blending the two sources together would expand the use of local well water and reduce reliance on expensive purchased water. However, co-mingling chloraminated water with chlorinated water presents two problems. The taste and smell of the finished water can be affected and the presence of residual chlorine can be reduced when the free chlorine residual reacts with the ammonia in the chloramine. EMWD realized that without changing the treatment method of their well water, blending would create serious problems. So, EMWD began working with Severn Trent Services to employ on-site chloramination. Severn Trent supplied their ClorTec on-site sodium hypochlorite generation system and an ammonia storage system for aqueous ammonia at 19 percent. These systems provided an efficient way to control both the chloramination and water blending process. By 2005, the district expects to convert all of their well sites to chloramination. To date, 9 of the 16 have been converted and use ClorTec units ranging from 100 lbs per day to one thousand lbs per day.