Chlorine is a very common, naturally occurring chemical element manufactured from sodium chloride. It is widely used for everything from creating household bleach to manufacturing computer chips to disinfection of swimming pools. Most water utility companies add chlorine gas to raw water to kill bacteria and other harmful microorganisms to prevent waterborne diseases. While necessary for safe water, chlorine creates many problems for foodservice operations:
Fortunately, chlorine is not difficult to remove from water. Carbon, found in many water filters, has remarkable capacity for neutralizing chlorine. Activated carbon is a mild reducing agent and chlorine is a strong oxidizing agent, so after chlorine becomes adsorbed, it then actually reacts with the carbon. The chlorine is reduced to chloride ion (as in table salt and sea water), one atom of carbon is oxidized to carbon dioxide, and both are released to the solution (desorbed). Meanwhile, most of the spots on the activated carbon, where all this took place, become “auto-regenerated” back to their original, like new condition, ready to adsorb again. For free available chlorine (FAC), this takes only about fifteen minutes, which means that a small amount of carbon can achieve an acceptable steady-state condition if the flow rate is slow or intermittent. For “combined chlorine” (chloramine), the reaction is much slower, and more carbon or more contact time is needed to achieve equivalent reductions.
- Chlorine gas has a very strong, pungent smell and an unpleasant taste. It is detectable in concentrations of as low as 1 part per million (ppm).
- Chlorine is an oxidizing agent, and is corrosive on metals in plumbing and foodservice equipment.
- Chlorine can cause damage to gaskets in equipment, making them brittle
- Chlorine reacts with natural organic compounds in the water to form potentially harmful chemical by-products such as trihalomethanes (THMs).
- Chlorine is not very effective at killing cysts, which are living organisms that can cause illness. Examples of cysts include Giardia and Cryptosporidium.
Chloramines are very common drinking water contaminants, and everybody is familiar with the foul taste & odor they create—at least from swimming pools, if not from drinking water. Usually their presence is not intended, but about 25% of the largest public water supplies in the U.S. add the simplest one, mono-chloramine, to the water on purpose. They use chloramine because it is more stable in water, allowing for disinfection over longer distances.
Chloramines are a family of disinfection by-products (DBPs), formed from the reaction of disinfectant chlorine with the nitrogen atom (N) in ammonia (NH3) or organic compounds containing a reactive nitrogen atom. There are many such biological chemicals in drinking water, mostly derived from the cellular debris from killed bacteria and algae. Mono-chloramine is the simplest and most common member of the group, often produced intentionally from the reaction of pure chlorine and pure ammonia.
Chloramines in general are undesirable in drinking water because they are toxic and because they smell and taste bad. However, monochloramine is tolerated because it is useful as a secondary disinfectant, and it is the least toxic and smelly of the group. Still, concentrations above 4.0 mg/L are prohibited. The usefulness of monochloramine comes from its comparative weakness as an oxidizing agent: it retains about 5% of free chlorine’s chemical power, which is not strong enough to use as a primary disinfectant, but it is still able to inhibit the re-growth of any survivors of disinfection. It is also too weak to corrode copper and brass plumbing materials, and therefore it lasts much longer in the mains—two or three days instead of just a few hours for free chlorine. Finally, monochloramine is chemically too weak to produce the other common disinfection byproducts—trihalomethanes (THMs), haloacetic acids (HAAs) and haloketones (HKs),, which may pose a health hazard.
Typically water utility companies use free chlorine (or chlorine dioxide or ozone) only in the early steps of water treatment. Then, at the end, just as the finished, treated water is about to leave the plant and go out into the water mains, pure ammonia is added to convert the free chlorine residual into chloramine. Without that final adjustment, the free chlorine would continue to produce unwanted THMs, etc. for several more hours and then be completely gone, leaving the system with no continuing protection.
Standard water treatment practice is to use ½ - 1 ppm of free chlorine or 1 – 2 ppm of monochloramine. Some systems attempt to counteract monochloramine’s weakness by using more of it, but all that does is increase the frequency of taste & odor complaints. There is not much difference between the smell of the two at low concentrations, but above 1 ppm the stink of monochloramine is very objectionable—much worse than free chlorine—and removing it is even more important than removing ordinary free chlorine, especially if the water is to be used for commercial food/beverage service.
Unfortunately, chloramine is more difficult to remove than plain free chlorine: it reacts only weakly and slowly with activated carbon, just like it does with everything else. That means that the water must stay in contact with the carbon much longer than if free chlorine alone was present. Many filters do not have enough carbon for the long contact time required to achieve removal. Only products with significant capacity will give satisfactory performance.
Everpure offers the CB20 line of filters for chloramine reduction. The CB20-302E and CB20-312E use a combination of Granular Activated Carbon (GAC) and submicron carbon block. These high capacity filter systems are NSF certified for chloramine, chlorine and taste & odor reduction: