[jabraben]

Our city uses Chlorine Dioxide for disinfecting the water supply and I have a question about how to remove it. In Martin Brungard's Water Knowledge page, in section 4.1.5, he says the following: "The design of an activated carbon filter system for chlorine compound removal is relatively simple. The residence time for water passing through the carbon media must meet certain minimum durations. For hypochlorite removal, the residence time should be at least 40 seconds. For chloramine removal, the residence time should be at least 6 minutes. Increasing these durations will improve the life of the media and increase the total volume of water that can be treated with the filter unit. (To provide an example of design recommendations for chloramine removal, kidney dialysis machine manufacturers typically recommend an 8-minute residence time for activated carbon, water pretreatment units) The residence time (also known as Empty Bed Contact Time) is calculated by dividing the volume of carbon media (say gallons or liters) by the flow rate (gal/min or L/min)."
He talks about residence time for hypochlorite removal and the residence time for chloramine removal but doesn't address chlorine dioxide directly so I'd like to know what the residence time, in this context, would be for water treated with chlorine dioxide. Anybody help me out?

[majorvices]

Maybe Martin will chime in here. I have never even heard of that as a disinfectant in public water before.

[mabrungard]

You guys are working me out!  I had to pull out my old college textbooks to confirm the answer.

While chlorine dioxide is a different chemical than the more common chlorine or chloramines, it eventually decays into the hypochlorite ion that is what chlorination produces. So someone that is supplied water that is disinfected via chlorine dioxide can assume that the same removal treatment methods used for chlorine are applicable. This is good news since activated carbon is very effective at treating chlorinated water and less effective at treating chloraminated water.

You can use the treatment information for chlorination with respect to brewing treatments.

[jabraben]

Thanks for responding both here and in the homebrewtalk forum, Mr. Brungard. I really appreciate the information.