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Bacteria in carbon filters
Moderator(s): John Hammerstrom
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Dr. Dennis Lye responds to bacteria question 0 J. Hammerstrom  An ARCSA member asked the following question:Should I expect trouble with bacteria growing in my carbon filter? Shouldn't I be using chlorine in my system? One person asked me how I was going to clean my carbon filter if I didn't plan on running chlorine through it.   I know you have to change the filters on a regular basis, but other than that, I don't know. ARCSA consulted former ARCSA President and current EPA Microbiologist Dr. Dennis Lye, PhD (who writes here for himself, and not representing EPA):Dr. Lye's response:Carbon filters are usually placed ahead of chlorine applications since the carbon filter will bind the chlorine and lower the disinfectant levels. Most users use carbon filters to remove any chemicals (not microbials) that might be causing taste/odor problems.    Carbon filters are typically meant to be used with water that has already received some type of disinfectant (for instance, to remove the chlorine taste in public water). However, our users have found that carbon filters work well with collected rainwater that has not received any type of disinfectant. Again, my comments are for well-designed and well-maintained systems that deliver a fairly clean source of water. They do not work well if your water source is more contaminated (such as stormwater).All filters become contaminated with microorganisms.  Carbon filters are rapidly colonized by microorganisms that are common to the system. We have tested many of the organisms that commonly colonize carbon filters and have found that they are usually not a source of risk to the users.           Short answer.  We do not know of any systems that apply disinfect "before” carbon filters.  Typically, do not "clean” carbon filters with chlorine. Carbon filters placed on well-designed, well-maintained rainwater collection systems have not been found to amplify organisms that are harmful to humans. However, the carbon filters may be colonized by bacteria that cause a heavy biofilm (filter is made ineffective by slime layer), or that release taste/odors that are a nuisance to the user.                  Our users have found that regular replacement of filters (as mentioned by the manufacturer) will give a satisfactory product.  Bacteria will grow on anyfilter placed on a rainwater system.  Rarely a problem.  Users should check the filter on a regular basis and decide for themselves on an appropriaterotation/replacement period.  We recommend that carbon filters not be used on rainwater systems unless the users are concerned about certain chemical (petrochemicals, insecticides, etc.) in the collected rainwater or they are having taste/odor problems.   
by J. Hammerstrom
Thursday, January 9, 2014
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