The Chloramine Challenge
Chloramine removal is near the top of the requests we get from city water customers. People are concerned and sometimes confused about chloramines.
Most of us are familiar with chlorine. For most of the 20th century, chlorine was the disinfectant of choice for public water supplies. Now it is being rapidly replaced by a substance called chloramine, a mix of chlorine and ammonia. The decline in the use of chlorine began with the relatively recent discovery of a group unsavory and often carcinogenic spin-off chemicals called trihalomethanes (THMs) that are formed when chlorine combines with organic matter in water. To meet EPA standards for THMs, which once created are hard to remove, municipal suppliers are turning increasingly to disinfection with chloramines, which produce much lower levels of trihalomethanes.
As often happens in our imperfect world, however, the solution to the THM problem brought its own set of problems. For example, chloramine can be deadly to fish in aquariums and ponds and to patients on dialysis machines. For regular home use, water with chloramine presents aesthetic issues of bad taste, odor and skin irritation. And let’s be frank: its long-term effect on health is largely unknown. Chlorine, after all, was added to water for decades before THMs were discovered.
For a variety of reasons, increasing numbers of people want chloramine out of the water they drink and bathe in.
One of the big myths about chloramine is that it can’t be removed. Actually, it is removed with filter carbon (often called charcoal), the same filtering agent that very effectively removes chlorine. The difference is that chloramine is much harder to remove. Therefore, it takes more carbon and water must be given more residence time in the carbon. In other words, you need a considerably larger carbon bed and a significantly slower flow rate to remove chloramine with standard carbon.
The challenge of chloramine and other difficult contaminants has led to the production of a modified carbon called catalytic carbon. Catalytic carbon is a specially processed filter medium designed to greatly enhance carbon’s natural ability to promote chemical changes in contaminants. Standard filter carbon reduces contaminants in two ways. It “adsorbs” chemicals by trapping and holding them, and to a smaller degree, it “chemisorbs” contaminants by changing them to something harmless. Chlorine, for example, can be “catalyzed” to harmless chloride.
Catalytic carbon retains conventional carbon’s ability to adsorb contaminants but it also possesses greatly enhanced capacity to catalyze, to promote beneficial chemical reactions. It is by catalytic action that chloramine is reduced.
Filter carbon performance is rated by several standards. Common performance measuring standards are the molasses number, the iodine number and the peroxide number. Catalytic capacity of carbon is expressed by the peroxide number, which measures the rate of decomposition of hydrogen peroxide by the carbon. The faster a carbon will break down hydrogen peroxide, the greater its catalytic activity. The lower the peroxide number the better.
The peroxide number of catalytic carbon can be as low as 8 and is seldom higher than 14. The peroxide number of conventional bituminous coal based carbon (the type most commonly used for chlorine reduction) is around 40, and other popular carbon have peroxide numbers around 120.
Catalytic bituminous-based carbon is the unchallenged best choice when it comes to chloramine removal.