Chlorinated Disinfection By-Products in Drinking Water According to Source, Treatment, Season, and Distribution Location

Article excerpt

Abstract: The occurrence of the most prevalent chlorinated disinfection by-products (DBPs) was investigated in three Quebec City distribution systems that deliver drinking water subjected to different treatment strategies. Trihalomethanes (THMs), haloacetic acids (HAAs), and other complementary parameters were monitored in several locations representing variable water residence times over 16 months. The occurrence of chlorinated DBPs levels was considerably lower in the system where raw water is subjected to pre-ozonation instead of pre-chlorination (as pre-treatment) or direct chlorination. Seasonal analysis of the data showed that according to the system and to the group of chlorinated DBPs, the average DBP concentrations in winter were two to four times lower than the average DBP levels of the entire period under study. Considerable variations of both DBP groups were observed according to the water residence time in the distribution system, but the behavior was not the same for THMs as for HAAs. In fact, correlations between THM and HAA levels were good only for cold water and low residence time conditions. Seasonal and spatial variations of DBPs documented in this study have important implications on regulatory issues and from an epidemiological point of view.

Key words: trihalomethanes, haloacetic acids, drinking water, distribution system, water treatment, source, season, location.

Resume: L'occurrence des sous-produits de la desinfection par le chlore (SPC) a ete examinee dans trois systemes de distribution de la Ville de Quebec (Canada) qui transportent de l'eau potable soumise a differentes strategies de traitement. Les trihalomethanes (THM), les haloacides acetiques (HAA) et d'autres parametres complementaires ont ete surveilles dans plusieurs endroits representant divers temps de residence de l'eau sur une periode de 16 mois. L'occurrence de SPC chlores est considerablement plus faible dans le systeme ou l'eau brute est soumise a un pretraitement par pre-ozonation au lieu d'une prechloration ou a une chloration directe. L'analyse saisonniere des donnees a montre que, selon le reseau et le groupe de SPC chlores, les concentrations moyennes de SPC en hiver etaient entre deux et quatre fois plus faibles que les niveaux moyens de SPC durant toute la periode de l'etude. Les concentrations des deux groupes de SPC variaient grandement selon le temps de residence de l'eau dans le reseau de distribution, mais les comportements des THM et des HAA etaient differents. En fait, les correlations entre les niveaux de THM et de HAA n'etaient elevees que pour l'eau froide et des courts temps de residence. Les variations spatiales et saisonnieres des SPC documentees dans la presente etude ont des repercussions importantes d'un point de vue reglementaire et epidemiologique.

Mots-cles : trihalomethanes, haloacides acetiques, eau potable, reseau de distribution, traitement de l'eau, source, saison, localisation.

[Traduit par la Redaction]

Introduction

Trihalomethanes (THMs) and haloacetic acids (HAAs) are the major disinfection by-products (DBPs) occurring in chlorinated drinking waters. They form ensuing reactions of chlorine with natural organic matter (NOM) and bromide. THMs include chloroform, dichlorobromomethane (DCBM), dibromochloromethane (DBCM), and bromoform; the sum of these four substances is denoted as total THMs. HAAs include nine substances, the mostcommonbeing dichloroacetic acid(DCAA) and trichloroacetic acid (TCAA). Other compounds, found generally at lower levels, are bromochloroacetic acid (BCAA), dibromoacetic acid (DBAA), monochloroacetic acid (MCAA), and monobromoacetic acid (MBAA). In the United States, the sum of DCAA, TCAA, DBAA, MCAA, and MBAA is commonly denoted as HAA5 (Chen and Weisel 1998). Nowadays, the occurrence of chlorinated DBPs is a major issue in the drinking water community because they are considered potentially carcinogenic, and since toxicological studies suggest they could cause adverse reproductive and developmental outcomes (Cantor et al. …