Characterization of organic precursors for chlorinous odor before and after ozonation by a fractionation technique

To identify the primary fraction of dissolved organic matter (DOM) responsible for chlorinous odor, waters treated by the conventional treatment (i.e., coagulation, flocculation, sedimentation and rapid sand filtration (RSF)) and ozonation were characterized by a fractionation technique prior to chlorination. Furthermore, chlorinous odor strengths originated from organic fractions were compared with that resulted from trichloramine (NCl3). Odor strengths and trichloramine concentrations were determined by the triangle sensory test and head space-GC/MS, respectively. The major DOM fraction for outlet water of RSF was hydrophobic acid (HoA), whereas the hydrophilic acid (HiA) fraction was dominant in the ozonated water. For a fixed DOC level (1 mgC/L), the base (Bas) or hydrophilic base (HiB) fraction was found to be the major organic precursor of chlorinous odor for the effluent of RSF. Even the mass percentages of DOM fractions in RSF water were considered, Bas was the major DOM fractions responsible for chlorinous odor. For ozonated water, two major precursors of chlorinous odor were HiA and hydrophilic neutral (HiN) fractions. Furthermore, the influence of trichloramine on chlorinous odor intensity for ozonated water should not be negligible. Under variation of seasonal organic contents, changes in precursors of chlorinous odor were observed.