Impact of bromide ion concentration, time, dissolved organic carbon and molecular weight cutoff on haloacetonitrile, haloketone, chloropicrin and trihalomethane formation potentials

Abstract

This research investigated the formation potential (FP) for haloacetonitriles (HANSs), haloketones (HKs), chloropicrin (CP) and trihalomethanes (THMs) under conditions of constant DOC, constant Cl:DOC ratio, variable [Br] and variable apparent molecular weight (AMW) for coagulated water from a full-scale water treatment plant. Coagulated, high humic water (4.5 mg DOC/L) was fractionated into <1K, <10K, and <30K MWCO fractions. The DOC of the fractions was adjusted to the same value (e.g., ~ 2 mg/L). Fractions were chlorinated at 3:1 Cl,:TOC ratio under varying [Br]. Observed, non-THM species occurred at low concentrations (<0.3-9.0 ug/L). As expected THMFP speciation was strongly affected by Br:Cl ratio; this research demonstrated similar effects on specific HANs and HKs. Increasing quantities of brominated HANs and HKs were observed with increasing [Br]. DCANFP remained relatively constant while BCANFP and DBANFP increased with increasing [Br]. Increases in brominated species resulted in a larger relative change in THANFP than TTHMFP, suggesting that more HAN precursor material reacted when Br was present. Elevating Br:Cl to 0.03 resulting in HANFPs comparable to CHBr,FP. Change in HAN and HK species with respect to molecular weight cutoff (MWCO) and coagulated-raw water comparisons suggest that HANFP results from reaction with small, reactive, nitrogen containing compounds (<1K AMW) and larger (<30,000 MWCO) proteinaceous matter.