Preliminary assessment of trihalomethanes(THMs) in the waters of Hong Kong

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Preliminary assessment of trihalomethanes(THMs) in the waters of Hong Kong


Author: Chan, Hok-kin
Title: Preliminary assessment of trihalomethanes(THMs) in the waters of Hong Kong
Degree: M.Sc.
Year: 1997
Subject: Drinking water -- China -- Hong Kong
Water -- Purification -- Chlorination
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Pages: x, 55, [58] leaves : ill., maps ; 31 cm
Language: English
Abstract: Free chlorine is a good disinfectant for drinking-water, and chlorination has been using for drinking-water disinfection in Hong Kong for many years. However, the problems of the formation of halogenated organic, particularly Trihalomethanes (THMs), during its use have caused the entire subject of drinking water disinfection to be reviewed. This paper described the present state of Hong Kong's drinking-water, international concerns about THMs and a brief review of recommended disinfection by-products (DBPs) control methods. Literature review of the chemistry of THMs and its formation parameters as well as health effects were also discussed. In order to assess the THMs level in Hong Kong's drinking-water, the standard testing method given by U.S. EPA, 6210D: Purge and Trap Capillary-Column Gas Chromatographic/Mass Spectrometric Method was chosen. A chemical analysis of finished water samples at fourteen selected locations was carried out from 1996 to 1997 so as to compare with the maximum contaminant level (MCL) set by the standard (100 ug/L) of Drinking-Water Quality Guidelines of the World Health Organisation (WHO). THMs concentrations in the range of 27.3 to 82.4 ug/L were recorded which increased with the concentrations of THMs precursors represented as Total Organic Carbon (TOC). The average THMs levels at fourteen selected sampling locations were obtained, and the effect of sampling locations on the THMs levels was dominated and more significant than that of seasonal factor. The highest THMs value of 94.4 ug/L was obtained at Yuen Long. All readings complied with the standard (100 ug/L) of Drinking-Water Quality Guidelines of the WHO. The contribution of Chloroform was about 88% by weight, and about 9% by weight for Bromodichloromethane. Only trace, about 2% by weight, Dibromochloromethane was recorded. Throughout the analytical experiment, the concentrations of Bromoform were lower than the MDL of the GC apparatus used in this project, that was 0.5 ug/L. For the samples collected from Northern New Territories where water source was mainly from Shenzhen reservoir, East River, the TOC & THMs levels were generally higher than that of local water supplies. The findings implied that the THMs level of drinking water within Hong Kong still complied with the WHO standard. Nevertheless, the potential hazard of THMs formation has to be studied and controlled especially for Northern New Territories where the water supply was mainly from Shenzhen reservoir, East River.

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