| Mechanisms and factors affecting disinfection byproduct (DBP) formation in drinking water treatment and distribution system are not well understood. This study investigates rapid phase (2 hours) and slow phase (2 to 48 hours) chlorine decay, DBP formation, and DBP compound speciation in the presence of model iron oxides. Batch experiments were conducted with goethite and magnetite, multiple finished waters, variable chlorine dose, and fixed pH 8. The overall objective was to elucidate the role of each model iron oxide and their relevance to current drinking water regulation and risk exposure.; In presence of water treatment plant finished water, the goethite surface increases the observed chlorine consumption in both the rapid and slow phases. Control reactions of goethite in absence of dissolve organic carbon do not show any chlorine decay, indicating goethite adsorbed natural organic matter (NOM) is responsible for chlorine decay in the aqueous-goethite system. Increasing ferrous site concentration in the goethite-magnetite mixture system increases chlorine consumption, meaning NOM interaction with this system produces additional chlorine reactive NOM sites in addition to the reaction of goethite adsorbed NOM, aqueous NOM, and ferrous site reaction with chlorine.; In presence of goethite, DBP formation in rapid phase is either equal or suppressed compared to water alone. However, DBP formation increases in aqueous-goethite system compared to water alone during the slow phase. This indicates the modification and increase of NOM sites forming DBP precursor while adsorbed onto the goethite surface. This hypothesis of modified and increased number of NOM reactive sites is supported by numerical simulation of chlorine and DBP formation kinetics. Total trihalomethane (TTHM) formation increases both in rapid and slow phase, with the greatest formation occurring during the slow phase. In presence of goethite, both dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) formation are increased in the slow phase over water alone. In presence of goethite-magnetite mixture, the ferrous sites (mostly from magnetite) competes with NOM for chlorine whereas ferric surfaces (goethite) act as a DBP enhancer by adsorbing NOM. Control reactions of DCAA with chlorine, NOM, goethite, and magnetite showed that there is an additional DCAA degradation that involves magnetite. (Abstract shortened by UMI.)... |
