This study investigates the role of bromide and the structure of precursors in DBPs formation. Resorcinol (1,3-dihydroxylbenzene) and 2,4-pentadiol were used to represent the aromatic and aliphatic precursors. Laboratory prepared hydrophilic organic acids was used to simulate the mixtures of the aqueous natural organic matter. The results showed that about 60% of the bromide was transformed into HOBr and OBr by chlorine when the chlorine dosages was high (5–20 mg/L of free chlorine). However, only 20% of bromide was transformed into HOBr and OBr at low chlorine dosage (1 mg/L). Trihalomethane formation potential (THMFP) measurements showed that higher THMs formation was obtained at higher pH for 2,4-pentadiol, mainly due to the presence of the bromo-THMs. For resorcinol, however, no bromo-THMs are formed at either pH 7 or 9. For THMFP from hydrophilic organic acids, no apparent pH effect was observed. It is concluded that the higher THM formation at higher pH was mainly due to the formation of bromo-THMs from the aliphatic precursors. Similar trends are obtained in THMFP measurements for haloacetic acids formation potential (HAAFP).

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