Catalytic and standard carbon for stripping free chlorine and chloramine ahead of membranes, resins and process water — a reaction duty, not an adsorption one.
One is fast and forgiving; the other decides the size of the vessel.
Free chlorine is reduced almost on contact, so a standard carbon at a few minutes of contact time will strip it reliably. Monochloramine reacts far more slowly, and a bed sized for free chlorine will let it through. Catalytic carbon, with a surface deliberately modified to accelerate the reaction, is what makes chloramine removal practical at a sensible vessel size.
4–8
minutes EBCT
Working contact time range across free chlorine and chloramine duty.
The carbon is one stage in a train, not the whole of it.
Whether the residual is free chlorine, chloramine or both is established first. The two require different grades and different contact times, and the wrong assumption sizes the vessel wrongly.
Free chlorine duty is designed at a few minutes; chloramine needs considerably more even on catalytic carbon. The bed is sized on the slower reaction present.
The bed runs continuously with residual monitored downstream. Because the mechanism is reaction rather than saturation, performance falls off gradually rather than breaking through sharply.
Beds are sanitised on a defined interval to control the biofilm that develops once the disinfectant is removed, and replaced when residual begins to appear downstream.
The grades that fit dechlorination grade — and what each is good at.
Surface modified · coconut or coal
Carbon with catalytic activity developed at the surface, accelerating the chloramine reaction enough to make removal practical at realistic contact times.
Coconut shell · 12x40
High-activity shell carbon for free chlorine duty, where the reaction is fast and the additional cost of catalytic activity is not warranted.
Acid washed · certified
The same duty with the extractables, ash and documentation a food, beverage or pharmaceutical water system has to satisfy.
What each property actually governs once the bed is running.
The governing design figure. Free chlorine sits at the low end, chloramine at the high end even with catalytic activity.
The measure of how far the surface has been modified to accelerate the reaction. It is what separates a chloramine grade from a standard one.
A finer cut than organics duty, since the reaction happens at the surface and available surface per unit volume is what matters.
Fines from a dechlorination bed go straight to a membrane or a resin bed, so attrition resistance is specified tightly.
Low ash keeps the treated water clean for the sensitive equipment downstream, and acid-washed grades are standard for this duty.
Secondary here, but relevant because these beds usually carry a taste, odour and trace organic duty alongside dechlorination.
Because the reaction between monochloramine and a carbon surface is far slower than the free chlorine reaction. Catalytic carbon has a surface modified to accelerate it, which brings the required contact time down from impractical to achievable at a realistic vessel size.
Roughly four to five minutes empty bed contact time for free chlorine, and considerably more for chloramine even on catalytic carbon. Where both are present, the bed is sized on the slower reaction.
It loses activity gradually rather than breaking through sharply, since the mechanism is surface reaction rather than saturation. Performance is tracked by monitoring residual downstream rather than by predicting a capacity.
Because the bed removes the disinfectant residual, leaving a warm, wet, high-surface-area environment with adsorbed organics. It is managed with a defined sanitisation interval and, in critical systems, by downstream disinfection.
Usually yes, and it is normal practice. The dechlorination duty determines the contact time, and the taste, odour and trace organic removal comes with it provided the grade has the adsorption capacity as well as the surface activity.
Send the residual species and concentration, the design flow and what sits downstream, and we will come back with the grade, the contact time and the vessel size.
