September 01, 2017 0 Comments
The USEPA require that both chlorine dioxide (ClO2) and chlorite (ClO2-) are monitored daily at the start of a distribution network and that chlorite is measured less frequently at various points throughout a network. Chlorate is not required, although is included under the Information Collection Rule.
The following are methods that have been approved by the USEPA for ClO2 monitoring:
As DPD has been removed as a standard method for determining ClO2 by the AWWA Standard Methods committee, the EPA will also probably remove it sooner rather than later.
As for chlorite, there are a few methods (such as ion chromatography) approved for chlorite monitoring. None of them are truly portable as the ChlordioX Plus is making it the only portable USEPA approved method for determining chlorite.
Standard Method (4500 -ClO2 Method C) - Amperometric titration is an electrochemical method that measures current flow when a fixed voltage is applied to an electrode. By measuring the current whilst carrying out a titration with phenylarseine oxide, each oxychlorine species can be separated out and quantified. However, Method C has now been removed as an EPA approved method for measuring chlorine dioxide in drinking water due to inherent weaknesses in the test method.
Amperometric Method (4500 - ClO2 Method E) - Principle is as per Method C and the procedure is also similar but the inherent test weaknesses are avoided. This method is the standard method which all the ChlordioX Plus evaluations were compared to and is the industry standard method. In theory, as well as chlorine dioxide, chlorine and chlorite, chlorate can also be carried out using this method but it is complicated and therefore usually carried out via ion chromatography.
Other colorimetric methods are available however none are approved for compliance testing.
This summary of methods is based on White’s Handbook of Chlorination and Alternative Disinfectants by the Black and Veatch Corporation, published by Wiley in 2010.
See here for a list of EPA methods approved for chlorine dioxide and chlorite monitoring under the alternative test methods program
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