Impact of chlorine exposure time on disinfection byproduct formation in the presence of iopamidol and natural organic matter during chloramination.

Chloramines, in practice, are formed onsite by adding ammonia to chlorinated drinking water to achieve the required disinfection. While regulated disinfection byproducts (DBPs) are reduced during chloramine disinfection, other DBPs such as iodinated (iodo-) DBPs, that elicit greater toxicity are formed. The objective of this study was to investigate the impact of prechlorination time on the formation of both halogen-specific total organic halogen (TOX) and iodo/chlorinated (chloro-) DBPs during prechlorination/chloramination in source waters (SWs) containing iopamidol, an X-ray contrast medium. Barberton SW (BSW) and Cleveland SW (CSW) containing iopamidol were prechlorinated for 5-60 min and afterwards chloraminated for 72 hr with ammonium chloride. Chlorine contact time (CCT) did not significantly impact total organic iodine (TOI) concentrations after prechlorination or chloramination. Concentrations of total organic chlorine (TOCl) formed during prechlorination did not significantly change regardless of pH and prechlorination time, while TOCl appeared to decrease after 72 hr chloramination period. Dichloroiodomethane (CHCl2I) formation during prechlorination did not exhibit any significant trends as a function of pH or CCT, but after chloramination, significant increases were observed at pHs 6.5 and 7.5 with respect to CCT. Iodo-HAAs were not formed during prechlorination but were detected after chloramination. Significant quantities of chloroform (CHCl3) and trichloroacetic acid (TCAA) were formed during prechlorination but formation ceased upon ammonia addition. Therefore, prechlorination studies should measure TOX and DBP concentrations prior to ammonia addition to obtain data regarding the initial conditions.

Formation of DBPs and halogen-specific TOX in the presence of iopamidol and chlorinated oxidants.

Iopamidol is a known direct precursor to iodinated and chlorinated DBP formation; however, the influence of iopamidol on both iodo/chloro-DBP formation has yet to be fully investigated. This study investigated the effect of iopamidol on the formation and speciation of halogen-specific total organic halogen (TOX), as well as iodo/chloro-DBPs, in the presence of 3 source waters (SWs) from Northeast Ohio and chlorinated oxidants. Chlorination and chloramination of SWs were carried out at pH 6.5-9.0 and, different iopamidol and dissolved organic carbon (DOC) concentrations. Total organic iodine (TOI) loss was approximately equal (22-35%) regardless of SW. Total organic chlorine (TOCl) increased in all SWs and was substantially higher in the higher SUVA254 SWs. Iopamidol was a direct precursor to chloroform (CHCl3), trichloroacetic acid (TCAA), and dichloroiodomethane (CHCl2I) formation. While CHCl3 and TCAA exhibited different formation trends with varying iopamidol concentrations, CHCl2I increased with increasing iopamidol and DOC concentrations. Low concentrations of iodo-acids were detected without discernible trends. Total trihalomethanes (THMs), total haloacetic acids (HAAs), TOCl, and unknown TOCl (UTOCl) were correlated with fluorescence regional volumes and SUVA254. The yields of all these species showed a strong positive correlation with fulvic, humic, and combined humic and fulvic regions, as well as SUVA254. Iopamidol was then compared to the 3 SWs with respect to DBP yield. Although the SUVA254 of iopamidol was relatively high, it did not produce high yields of THMs and HAAs compared to the 3 SWs. However, chlorination of iopamidol did result in high yields of TOCl and UTOCl.