AN UNIDENTIFIED CHLORAMINE DECOMPOSITION PRODUCT .1. CHEMISTRY AND CHARACTERISTICS

This paper reports on a study of the chemistry and structural characte ristics of an unidentified product found in organic free aqueous solut ion in the chloramination disinfection of drinking water. Mass balance on decomposing chloramine solutions were made using spectrophotometri c, titrimetric and ion chromatographic methods in the presence and abs ence of added nitrite. The concentration of the unidentified product w as determined from the difference of the measured and predicted chlora mine spectra. Nitrite is believed to have an important role in the for mation of the unidentified product. Added nitrite can dramatically inc rease the concentration of this product, and it is believed that nitri te may be involved in its formation during slow chloramine decompositi on. Nitrite is not expected to be stable in the presence of chloramine s as predicted from prior studies. Nitrite was observed, however, in r apidly decomposing solutions of dichloramine. Nitrate, chloride and ni trite were observed in photolysis of the unidentified product. The uni dentified product contains both nitrogen and chlorine, and has an esti mated molar absorptivity of 5000 M(-1) cm(-1) from the mass balance of chloride if one chlorine per molecule is assumed. Nitrate was also ob served along with the unidentified product in slow chloramine decompos ition at near or above neutral pH; however, the unidentified product w as not detected in chloramine solutions at pH 3.5, but nitrite was obs erved. The formation of the unidentified product is not believed to be acid or base catalyzed, but is proportional to the total oxidant lost in slow monochloramine decomposition. Monochloramine is not likely in volved in the rate-limiting step in the formation of the unidentified product.