Odor produced by breakpoint chlorination in a drinking water purification process was researched. Ammonia and six amino acids (glycine, alanine, valine, leucine, arginine, proline) were chlorinated and production of odor and its change were investigated. An intense odor which was different to the odor of residual free chlorine was detected after the chlorination of ammonia. The production of the odor was affected by pH and chlorine dose rate. While the intense odor was not produced in the breakpoint chlorination at pH 8.3, a weak odor before the breakpoint and the intense odor after the breakpoint were produced at pH 6.5. At pH 3.0, the intense odor was detected even in a sample of low chlorine dose rate. An identification of the intense odor substance was done using a gas chromatograph-mass spectrometer and trichloramine or a dimer of dichloramine was suspected as the odor causing substance. In chlorination of the six amino acids, the intense odor and its change were different according to each amino acid. Production of chlorinated intermediate and final products which had a different odor were suspected as one of the reasons.
Musty-odorous compounds, metabolites of some species of blue-green algae, are usually contained in both the water and algal cell bodies. The compounds in the latter solid phase were found to be easily removed by coagulation and sedimentation without breakpoint prechlorination (intermediate chlorination used instead). Chlorination of the algae results in an artificial release of the metabolite content into the surrounding water. When a large fraction of the compounds was present in the algal cell bodies, more than 60% of these compounds were removed in the intermediate-chlorination treatment. Powdered activated carbon treatment is effective in removing the compounds in the aqueous phase. However, the effectivness was usually limited in practical treatment to high concentrations of musty odor. On the other hand, the ozonation and granular activated carbon (GAC) treatment was found to be an effective method for removal. It was observed that the musty-odorous compounds were completely removed through the ozonation and GAC treatment system, which included coagulation and sedimentation without prechlorination.
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