Identification and fate of mixed ozonation/chlorination and ozonation/chloramination by-products in drinking water treatment.

摘要

Disinfection may cause a dilemma for drinking water treatment plants using chlorine for the maintenance of a disinfectant residual in distribution systems. On one hand the chlorine residual should ensure microbially safe drinking water, but on the other hand harmful disinfection by-products (DBPs) can be formed from the reaction of natural organic matter (NOM) with chlorine.; Many utilities are looking to the combined use of ozonation for primary disinfection, followed by chlorine or chloramines as a means of minimizing DBP formation while maintaining a stable disinfectant residual. However, these combinations may lead to a new spectrum of by-products that differs from that produced when a single disinfectant is used. The formation of mixed ozonation/chlorination and ozonation/chloramination by-products is the subject of this dissertation.; A diverse collection of precursor compounds that produce a large amount of “unknown” total organic halides (TOX) was identified by performing bench scale tests to simulate chlorination of known ozonation by-products. Simple mono- and di-carboxylic acids were not found to react with chlorine. Di-aldehydes, α-keto-acids, and α-hydroxy-acids are oxidized by chlorine but do not show TOX formation. However, chlorine does become incorporated in β-diketones. Oxalacetic acid, 3-methyl-2,4-pentanedione, acetonedicarboxylic acid, and malic acid were found to form more “unknown TOX” than common chlorination by-products. Usually, the chlorine demand as well as the TOX increase with decreasing pH and increasing chlorination time.; The identification of “unknown TOX” was the second major goal of this work. Quenched samples from the model compound studies were derivatized with pentafluorobenzylhydroxylamine (PFBHA), extracted with methyl-tert-butyl-ether (MtBE), and silylated with bis-(trimethylsilyl)-triflouroacetamine (BSTFA). Malic and acetonedicarboxylic acids were each found to produce a previously-unknown byproduct after reacting with chlorine. The identity of this and other new by-products was suggested based on the mass spectra. Surprisingly, mono-chlorinated species were found to be more abundant than di-chlorinated species in all cases.; The third phase of this research showed that a substantial amount of “unknown TOX” is also formed in distribution systems where chlorine is used as final disinfectant. The “unknown TOX” ranged between 60% and 80% of the measured TOX.