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Chlorine SOP for Wastewater samples
Tracy Herring
Posted: Wednesday, December 29, 2010 8:31 AM
Joined: 10/2/2009
Posts: 1

I am trying to meet all of the requirements for analyzing chlorine for a wastewater plant.


I typically work with drinking water and the Texas rules are very specific on method, acceptable colorimeters, accuracy, calibration requirements for handheld versus inline devices - but I can not find similar information for wastewater sampling.


I would like to be able to use the HACH colorimeter for chlorine testing, but are you required to do a manganese correction?  We used to do titrations and I think that was a requirement at one time.


Any guidance in the right direction is appreciated.






James Royer
Posted: Wednesday, December 29, 2010 12:13 PM
Joined: 9/21/2009
Posts: 98

We use the ampherometric titration method so that we avoid interferences. If you do colorimetric methods manganese will interfer.


In the past I have done colorimetric analysis for process control and corrected for nitrite and manganese. Set up two samples for analysis. One will be the sample and the other a blank. To the blank add a couple drops of 5% sodium arsenite solution to dechlor the sample. Then you add color reagent to both sample and blank. After color development add the same amount of arsenite solution to the sample. Read the difference between sample and blank and this is the chlorine residual.


Arsenite will reduce the chlorine but not remove the developed color. Manganese will produce color in both sample and blank. Arsenite will remove nitrite color. This is an old method from the 60's.