Selective Chlorination of Natural Organic Matter:
Identification of Previously Unknown Disinfection Byproducts
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Abstract
Natural organic matter
(NOM) serve as precursors for disinfection
byproducts (DBPs) in drinking water production making NOM removal
essential in predisinfection treatment processes. We identified molecular
formulas of chlorinated DBPs after chlorination and chloramination
in four Swedish surface water treatment plants (WTPs) using ultrahigh
resolution Fourier transform ion cyclotron resonance mass spectrometry
(FT-ICR-MS). Chlorine-containing formulas were detected before and
after disinfection and were therefore classified to identify DBPs.
In total, 499 DBPs were detected, of which 230 have not been reported
earlier. The byproducts had, as a group, significantly lower ratio
of hydrogen to carbon (H/C) and significantly higher average carbon
oxidation state (C<sub>OS</sub>), double bond
equivalents per carbon (DBE/C) and ratio of oxygen to carbon (O/C)
compared to Cl-containing components present before disinfection and
CHO formulas in samples taken both before and after disinfection.
Electrophilic substitution, the proposed most significant reaction
pathway for chlorination of NOM, results in carbon oxidation and decreased
H/C while O/C and DBE/C is left unchanged. Because the identified
DBPs had significantly higher DBE/C and O/C than the CHO formulas
we concluded that chlorination of NOM during disinfection is selective
toward components with relatively high double bond equivalency and
number of oxygen atoms per carbon. Furthermore, choice of disinfectant,
dose, and predisinfection treatment at the different WTPs resulted
in distinct patterns in the occurrence of DBP formulas