At our facilities we use what we believe to be a standard calculation to determine the amount of carbon to use to provide a 5 minute empty bed contact time: EBCT = Carbon (cu.ft)x 7.48/flow rate (gpm). It seems to me that there is another variable not accounted for in this equation . . . actual chloramine levels in the city water. If your in-coming water has routinely been around 2.0ppm of chloramines and the municipality decides to DOUBLE that level, does the above equation still apply? We are beginning to go through a lot of carbon for what is apparent break through.

the formula you are using is correct. however, you should have an absolute minimum of 10 minutes of EBCT. if that is still not sufficient, additional carbon tanks would need to be added until your chlorine/chloramine is under acceptable limits.

WNY-AKC Chief Tech,

We have five minute EBCT per tank for a total of 10 minutes. The apparent breakthrough is in between the tanks. Post tank #2 the levels are fine. We are contemplating using a series/parallel tank set-up with four tanks with 5 minute EBCT per tank. In this way if we have the same or similar amount of carbon per tank, the flow rate is essentially one half of what it was. Any thoughts on how the formula is affected by the incoming chloramine levels being twice what they were a year ago. My sense is the municipalities will add whatever they feel is needed to sanitize water to safe DRINKING levels. 3ppm? 4ppm? 6ppm??? At what point will the incoming levels overwhelm the formula?

Filtration has and is still calculated using flow per sq.ft. of surface area. This is great when you have a filter that is 10 ft x 10 ft. Smaller round tanks are a little harder to figure. (There are cheat charts out.) So California originally came up with a standard. Two tanks in series each having an EBCT of 3 minutes for Free (Carbon loves to remove Free Chlorine) and 5 minutes for Chloramine. To make it easier (or maybe just to change it) the fda said two tanks of equal size having a total EBCT of 6 minutes for Free and 10 minutes for Chloramines.

The fact is, Chloramine usage started as the city supply lines grew in length and the utilities were unable to hold a Chlorine level at the end of the main. Anyway, city mains are still growing in length and increasing levels are being seen closer to the processing centers. So is the current 10 minute standard sufficient? Probably not. Many systems have gone to 15-18 minutes to hold the increases they are seeing and the spikes that occur.

Always remember that the Total Chlorine test is a total of the Free and cchlorine compounds (Chlorine can tie up with stuff other than Ammonia and yes there are naturally occurring chlorine compounds out there although usually in minimal amounts.) So the question is whether the Total has risen or the suspected (isn't that a great word?) Chloramines (Total - Free)? Or has the Free taken a rise? (Doubtful) Then there is always the pH. Carbon performance takes a nosedive when the pH goes up.

Trust me on one thing. Here's the Deal. Someone in the water utility is responsible for ever penney they spend. Adding excess chemicals for no reason does not a hero make. There is a reason or they wouldn't be doing it. Or the operator's replacement wouldn't be anyway. When in doubt call and ask. Call the water lab. They are the one's that draw the samples and sign the reports. They like to talk about how smart they are usually and will provide you with a lot of detail if you go about it right. There are interfering chemicals (Magnesium, Bromine, about any of the -ine family) which can provide a false positive on a Chlorine test.

So much for that. Take care. Life is GOOD !!

Willie Burcham
wburcham1@aol.com

Willie,

Thanks for the input. As far as interfering chemicals are concerned, how do you test for that? If you cannot prove that the "color" of your test is not the result of one of these chemicals, how do you convince a surveyor that your test readings are not false positives? Also, we will be increasing our EBCT to handle higher city chloramine levels.

Mark

Look in the instruction manual for your test kit. If you don't have the manual, call the manufacturer of the kit, while you're getting your info, be sure to get a manual. Seriously, I know the info is in the Hach manual and there are a couple of other agents that you will need to complete the test. They will mask the interfering chemicals and take them out of the equation.

Being an approved method of analysis from the kit manufacturer, the surveyor has no choice but to accept the results.

Take Care
Life is GOOD

Willie B