Characterization of total organic halogen produced by chlorine, chloramines, and chlorine dioxide
Total organic halogen (TOX) is an analytically defined measurement that can provide an estimate of total organic bound halogen in water. The analysis of TOX in drinking water indicates that a large amount of the TOX formed during disinfection processes cannot be attributed to known specific disinfection byproducts. There has been a concern over the impact that the unknown fraction of TOX might have on human health. The standard TOX method cannot differentiate organic chlorine, bromine, and iodine. Ion chromatographic (IC) detection has been proposed for the halogen specific TOX analysis.
The first objective of this research was to determine the optimum TOX protocol for use with IC detection to analyze total organic chlorine (TOCl), bromine (TOBr), and iodine (TOI). The pyrolytic analyzer using pure O 2 and off-line IC combined with a standard TOX carbon (coconut based) worked best for the differential TOX analysis.
The second objective of this research was to assess the impact of bromide and iodide concentrations, different oxidation scenarios, and reaction conditions on the formation of unknown TOX. Chloramines and chlorine dioxide produced byproducts with a higher percentage of unknown TOX than free chlorine. Free chlorine formed more TOCl and TOBr than chloramines and chlorine dioxide in the presence of bromide. However, chloramines and chorine dioxide produced more TOI than chlorine and ozone in the presence of iodide.
The third objective was to characterize unknown TOX precursors using resin (XAD-8, XAD-4) extraction and ultrafiltration methodologies. Hydrophobic and high molecular weight natural organic matter (NOM) was found to be a more important precursor for unknown TOX formation than hydrophilic and low molecular weight NOM.
The forth objective was to determine the size and hydrophobicity of unknown TOX in drinking water. Total organic halogen from several finished waters was isolated using XAD resins and ultrafiltration membranes. A large fraction of the unknown TOX was comprised of hydrophilic compounds with high molecular weights. Ultrafiltration membranes were found to reject TOX compounds with molecular weights substantially below the membrane cutoffs. Neglecting this effect can lead to overestimation of the molecular size of TOX compounds.
0775: Environmental engineering