Steve Peck, Technical Manager, AXEON Water Technologies
In order to safeguard the public from bacteria or other microorganisms contaminating the municipal water supply, water utilities disinfect the water exiting the water treatment system into the distribution piping. The most common disinfectants are chlorine and chloramines due to their long residence time. Residual chlorine or chloramines remain present in the water from the water treatment plant to the point of use in a household or business.
Chlorine however reacts readily with naturally occurring dissolved organic matter in the water. In some cases, trihalomethanes (THM) such as chloroform are formed as a result. These THMs are considered potentially harmful to public health. In response, water utilities facing stringent regulations under EPA’s Disinfectants/Disinfection Byproducts Rule switched to the use of chloramines.
Municipal water utilities prepare chloramines in low concentrations by reacting free chlorine with ammonia. The resulting chloramine is more stable and does not dissipate as rapidly as free chlorine.
For many uses of water, it is desirable to remove chlorine and chloramines. For example, these chemicals can cause anemia in the aquatic life in aquariums, they can stunt the growth of plants and when brewing beer, they react with phenols in the malt resulting in a medicinal or plastic-like taste.
Chlorine is known to cause oxidation damage to reverse osmosis (RO) membranes. Exposure of membranes to chlorine is measured in terms of 1 ppm chlorine in water for 1 hour. Generally speaking RO membranes may show deterioration (i.e. increased TDS passage) after 1000 ppm-hours of free chlorine exposure. For this reason, free chlorine levels must be held below 0.1 ppm. RO membranes are able to withstand a higher level of chloramines (1 to 2 ppm) versus chlorine (0.1 ppm) before incurring irreversible damage. However, the presence of metals such as iron or aluminum in water can act as catalysts and accelerate the oxidation of membranes even at low concentrations of chloramines.
As mentioned, chloramine is formed by reacting chlorine with ammonia. Excess free ammonia remaining from this process or released after chloramines reacts with organics in the distribution system can cause temporary swelling of the RO membrane resulting in an increase passage of TDS in the permeate stream.
Chlorine can be removed using typical activated carbon. AXEON Carbon Systems or AXEON Carbon Block filter cartridges are an effective choice in removing chlorine. Activated carbon can also remove chloramines; however, the amount of activated carbon needed to provide sufficient contact time to remove chloramine is about four to five times that needed to remove chlorine.
AXEON therefore also offers a range of cartridges specifically designed for chloramine removal. These cartridges contain catalytic carbon, a special type of carbon with catalytic activity enhanced beyond that of conventional activated carbon. The chloramine removal efficiency of catalytic carbon significantly reduces the contact time and thus the required size of the cartridge. Theoretically, the catalytically-active sites within this carbon accelerate the decomposition of chloramine into traces of nitrogen gas, ammonia gas and chloride.
For more information, please contact us at 800-320-4074 or by email firstname.lastname@example.org.