Factors influencing disinfection by-products formation in drinking water of six cities in China

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Abstract

Based on the measured chemical and physical data in drinking water from six cities in China, the factors including total organic carbon (TOC), ultraviolet absorbance at 254 nm (UV254), pH, applied chlorine dosage, temperature, concentrations of bromide ion and several chemical elements which possibly affect the formation of trihalomethane (THM) and haloacetic acid (HAA) have been studied. The results showed that: in all factors, TOC and UV254 have definite correlations with total THM, but have nonsignificant relationships with total HAA. In the studied pH range of 6.5–8.5 for drinking water, the total THM concentration increased with the increasing of pH value, but the total HAA concentration slightly decreased. A low but significant relationship (r = 0.26, p < 0.01) occurred between total THM and applied chlorine dosage. Similar relationship (r = 0.21, p < 0.01) was found between total HAA and applied chlorine dosage. When the water temperature was low, the variation of THMs and HAAs was little, but in warmer water, the concentration of THMs and HAAs varied quickly. The extent of bromine incorporation into the DBPs increases with increasing bromide ion concentration. Based on the effect of chemical elements for the DBPs remove effect, the polyferric chloride could be a preferred flocculant agent in waterworks.

Introduction

Chlorine, the most widely used disinfectant for drinking water in China, will give rise to trihalomethanes (THMs) and haloacetic acids (HAAs), two most prevalent disinfection by-products (DBPs), when it is added to the drinking water as a disinfectant. THMs include chloroform (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM) and bromoform (TBM). Total trihalomethanes (TTHM) refer to the sum of these four chemical substances. HAAs include nine substances, only five of them are regulated by the current Disinfectants/Disinfection By-Products (D/DBP) Rule due to limited formation and occurrence data for some of the species [1]. The five HAAs are monochloro- and monobromo-acetic acid, dichloro- and trichloroacetic acid, and dibromoacetic acid (MCAA, MBAA, DCAA, TCAA, and DBAA, respectively). The main species of HAAs in drinking water are DCAA and TCAA and others are generally found at lower levels. The sum of DCAA, TCAA, DBAA, MCAA and MBAA is commonly denoted as total haloacetic acids (THAA). Some epidemiologic studies [2], [3], [4] have shown an association between long-term exposure to disinfection by-products and increased risk of cancer and potential adverse reproductive effect. Many researches indicated that DBPs in the drinking water were affected by natural organic matter (NOM), which is generally measured as total organic carbon (TOC) and ultraviolet absorption at 254 nm (UV254), pH, water temperature (T), bromide concentration (Br), chlorine dosage (Cl2) and residence time (t) [5], [6], [7], [8], [9], [10]. In the past, most of researches on disinfection by-products were from laboratory-scaled studies [11], [12], [13], [14], [15]. But the conditions of the laboratory-scaled studies were great different from that of the water on local waterworks. The results of studies could not fit in with the sample that was obtained from the local waterworks.

The primary objective of this study was to determine water quality parameters of drinking water of local waterworks from six selected cities of China and assess the effects of some water quality and operational parameters on HAA and THM formation.

Section snippets

Experimental design

Water samples used in this study were collected from the water treatment plants in Daqing, Beijing, Tianjin, Zhengzhou, Changsha and Shenzhen cities. These waterworks were selected to provide waters with different TOC and UV254 values as well as geographical differentiation. A total of 41 treatment plants were sampled both in summer and winter. For all waterworks, six samples (raw water, treated water before chlorination, treated water following chlorination, finished water, water between the

Results and discussion

The water quality parameters and disinfection by-products of drinking water for six selected cities in China are presented in Table 1, Table 2. The average values of TTHM and THAA in six cities of China are similar to that of drinking water in Korea [19] but are lower than that of drinking water in Pennsylvania (USA) [20], Istanbul (Turkey) and Salerno (Italy) [21]. Table 2 shows that pH and Br values are higher in north of China (Daqing, Beijing, Tianjin and Zhengzhou) than that in south

Conclusions

This study elucidated that: The THMs and HAAs formation are influenced by many water quality parameters including TOC, UV254, pH, water temperature, residence time, residual chlorine, bromide ion concentration and chemical elements.

The correlations between THMs formation and natural organic matter (TOC and UV254) are significant positive correlation (p < 0.01 and p < 0.05). And there is poor significant positive relationship between HAAs formation and natural organic matter (TOC and UV254) (p = 0.25

Acknowledgements

The authors thank the CDC of Daqing, Beijing, Tianjin, Zhengzhou, Changsha and Shenzhen cities for field and laboratory technical support. Funding and support for this project was provided by NSFC (Grant No.40771015), the National Science Foundation for Post-doctoral Scientists of China (Grant No.20070420520) and Key International Science and Technology Cooperation Projects (Grant No. 22007DFC20180). The authors also gratefully acknowledge the support of K.C. Wong Education Foundation, Hong

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