Chloramine Removal Using Activated CarbonBy: Michael Urbans
We recently had an application where chloramine removal from the water was critical. You think you know everything until you don’t.
To meet tougher THM (trihalomethane) standards municipalities are moving to chloramine disinfection. Chlorine creates higher levels of trihalomethanes. Chloramine is more stable and a much weaker oxidant so resultant THM levels are lower. Makes sense in the big picture – protects the consumer by reducing the cancer-causing disinfection byproducts.
Drill down and it’s a little more complicated.
• In potable water, chloramine can exist as monochloramine, dichloramine and trichloramine.
• Because municipal water is delivered with a pH between 6 and 9, monochloramine is the predominant species used for disinfecting.
• Monochloramine is also the most difficult type of chloramine to remove using carbon.
Enter the homeowner who wants to remove all traces of chloramine (or chlorine) and the THMs from their city water. No problem? Think again.
In a side by side comparison of standard and catalytic carbon the removal efficiency is initially the same. However, on standard carbon a slower removal rate occurs as the catalytic sites are used up (and supplanted by carbon oxides).
Because the chloramine reaction is catalytic in nature, activated carbons with enhanced catalytic activity are more efficient, last longer and enable you to use smaller equipment.
• Before prescribing the correct solution, ask the question – are we removing chlorine or chloramine?
• Chlorine -> Activated Carbon – 12×40, coal, coconut (piece of cake).
• Chloramine -> Catalytic Carbon such as Centaur® -> 12×40 in a smaller tank
BUT that wasn’t our problem.
The pH of the water we were treating was not between 6 and 9. It was around 4. Even though the water was being treated with carbon there was residual chlorine which set off alarms. If the pH was high, no problem. Our course we contacted the experts at Calgon for help. Their first question – Were we dealing with chlorine or chloramine?
Long story short – The municipal water being disinfected with chloramine. At the lower pH the species is trichloramine, or nitrogen trichloride.
With activated carbon the catalytic reaction with chloramine is opposite of chlorine.
• Chlorine destruction is enhanced at low pH.
• Chloramine destruction is enhanced at high pH.
The trichloramine was sneaking through the carbon because the pH was low. The solution – either raise the pH or use a catalytically enhanced coal carbon such as Centaur® to resolve.