Assessment of the products of reactions of drinking water disinfectants with humic substances and trace organic contaminants

Abstract

This paper describes results of a pilot scale study undertaken to examine the effects of the disinfectants chlorine, chloramines, chlorine dioxide and ozone on drinking water quality. Samples for testing were produced in a pilot plant having four parallel streams, one for each disinfectant, and each stream included a granular activated carbon (GAC) treatment step. Water samples were concentrated on XAD-2 resin and the disinfectants were evaluated by GC/MS analysis in parallel with mutagenicity screening using the Ames Salmonella assay. The results reported herein are for the first few months of the study, involving winter and spring thaw conditions. Except on one occasion, the winter water was non-mutagenic prior to oxidant addition. Mutagenic activity was generally present following chlorine addition but was always eliminated by S9 treatment. During spring thaw conditions when DOC, humic acid and extractable organics concentrations were highest the chlorinated samples were either toxic or mutagenic. When the reference stream was not mutagenic the S9 fraction always eliminated this mutagenicity. No mutagenic response was observed during winter or spring thaw conditions in the chlorine dioxide and chloramine streams or following GAC treatment in any stream. GC analysis of XAD-2 eluates showed little change in the organic: matrix of the water following choramination, even during spring runoff when the number and concentration of organic compounds increased dramatically. Chlorine dioxide and chlorine addition produced changes in the chromatograms, and some compounds present only in the chlorine stream were tentatively identified.