Seasonal variations of trihalomethanes (THMs) in water distribution networks of Istanbul City

Seasonal variations of trihalomethane (THM) concentrations were investigated within distribution systems of the Buyukcekmece water treatment plant in Istanbul City (Turkey). The investigation was based on an intensive 30-week sampling program, undertaken during the spring, summer and fall of the year 2003. THMs and other water quality and operational parameters were monitored at points along the distribution system between the treatment plant and the system's extremity. The results showed that THM concentrations vary significantly between finished waters and water at the distribution network. When water temperature exceeds 24 degrees C in summer, the THM levels are 1.2-1.8 times higher than finished water, while when water temperature is below 15 degrees C in the spring and fall, the measured THM concentrations at the system's extremity were very rarely higher than 100 mu g/L. Finally, THM levels were measured at sampling points representing progressively greater travel times from the plant to the extremity of the distribution system. Multiple regression analysis was also conducted in order to estimate THMs from total organic carbon, temperature, and chlorine dose parameters. The regression model resulted in a R-2 value of 0.827

Differential UV Spectroscopy Approach

In this study, the changes in UV absorbance of water samples were characterized using defined differential UV spectroscopy (DUV), a novel spectroscopic technique. Chlorination experiments were conducted with water samples from Terkos Lake (TL) and Buyukcekmece Lake (BL) (Istanbul, Turkey). The maximum loss of UV absorbance for chlorinated TL and BL raw water samples was observed at a wavelength of 272 nm. Interestingly, differential absorbance at 272 nm (Delta UV272) was shown to be a good indicator of UV absorbing chromophores and the formation of trihalomethanes (THMs) resulting from chlorination. Furthermore, differential spectra of chlorinated TL waters were similar for given chlorination conditions, peaking at 272 nm. Thecorrelations between THMs and Delta UV272 were quantified by linear equations with R-2 values >0.96. The concentration of THMs formed when natural organic matter is chlorinated increases with increasing time and pH levels. Among all THMs, CHCl3 was the dominant species forming as a result of the chlorination of TL and BL raw water samples. The highest chloroform(CHCl3), dichlorobromomethane (CHCl2 Br), and dibromochloromethane (CHBr2 Cl) concentration were released per unit loss of absorbance at 272 nm at pH 9 with a maximum reaction time of 168 hours and Cl-2/dissolved organic carbon ratio of 3.2

Relationship among chlorine dose, reaction time and bromide ions on trihalomethane formation in drinking water sources in Istanbul, Turkey

We investigate the effects of factors such as chlorine dose, reaction time and bromide ions on the formation and speciation of trihalomethanes during the chlorination of Istanbul reservoirs such as Terkos lake water, Büyükçekmece lake water and Ömerli lake water. The experimental results showed that approximately 50% of trihalomethane formation was observed in the first 4 h of reaction time in chlorinated Terkos lake water, Büyükçekmece lake water and Ömerli lake water, respectively. Trihalomethane concentrations increased with increasing chlorine dosage and reaction time. Chloroform was the major trihalomethane species forming as a result of the chlorinated raw water samples. On the other hand, bromide ions play a great significant role in the distribution of trihalomethane species. The bromine and chlorine incorporation ratios were strongly related to natural organic matter precursors and bromide levels in Terkos lake water, Büyükçekmece lake water and Ömerli lake water. The percentage of bromine incorporation was much higher than that of chlorine in all chlorinated water samples

Assessment of trihalomethane formation in chlorinated raw waters with differential UV spectroscopy approach.

In this study, the changes in UV absorbance of water samples were characterized using defined differential UV spectroscopy (DUV), a novel spectroscopic technique. Chlorination experiments were conducted with water samples from Terkos Lake (TL) and Büyükçekmece Lake (BL) (Istanbul, Turkey). The maximum loss of UV absorbance for chlorinated TL and BL raw water samples was observed at a wavelength of 272 nm. Interestingly, differential absorbance at 272 nm (ΔUV₂₇₂) was shown to be a good indicator of UV absorbing chromophores and the formation of trihalomethanes (THMs) resulting from chlorination. Furthermore, differential spectra of chlorinated TL waters were similar for given chlorination conditions, peaking at 272 nm. The correlations between THMs and ΔUV₂₇₂ were quantified by linear equations with R² values >0.96. The concentration of THMs formed when natural organic matter is chlorinated increases with increasing time and pH levels. Among all THMs, CHCl₃ was the dominant species forming as a result of the chlorination of TL and BL raw water samples. The highest chloroform (CHCl₃), dichlorobromomethane (CHCl₂Br), and dibromochloromethane (CHBr₂Cl) concentration were released per unit loss of absorbance at 272 nm at pH 9 with a maximum reaction time of 168 hours and Cl₂/dissolved organic carbon ratio of 3.2

Seasonal variations of NOM composition and their reactivity in a low humic water

Natural organic matter (NOM) and its potential to form disinfection by-products (DBPs) during water treatment are of great public health concern. Understanding the seasonal changes in NOM composition and their reactivity in DBP formation could lead to a better treatment of drinking water and a more consistent water quality. NOM from the Terkos Lake was fractionated and characterized by XAD resin adsorption and ultrafiltration (UF) techniques during four different seasons within a year. XAD fraction analysis indicates that the HPI (38%) and the TPI (21%) were the dominant chemical fractions as DOC masses across the sampling period. Moreover, the fractions contributing to the most UV254 absorbance were HPO, which accounted for more than 72% of total UV254. It was found that the percentages of UV254 of HPI and TPI showed significant amount of variation with coefficients of variation of 48% (HPI) and 35% (TPI), respectively. Moreover, it was concluded that the HPO fraction was the primary THM precursor, which contributed more than 48%, and while the primary fraction of HAA precursors was found to be TPI, accounting for more than 47% of total HAAFP with exceptions in January 2011. As obviously seen in this study, the hydrophobic constituents in Terkos Lake water are on the low end of the spectrum in terms of their reactivity to form HAAs. In the context of THM reactivity, the physical properties (i.e., moleculer size) of Terkos Lake NOM are more important than their chemical properties (i.e., aromaticity). On the other hand, the predominant fraction as the source of HAAs precursors was found to be with the TPI and HPI chemical fractions. © 2013 American Institute of Chemical Engineers

Natural organic matter removal and fouling in a low pressure hybrid membrane systems.

The objective of this study was to investigate powdered activated carbon (PAC) contribution to natural organic matter (NOM) removal by a submerged MF and UF hybrid systems. It was found that filtration of surface waters by a bare MF and UF membranes removed negligible TOC; by contrast, significant amounts of TOC were removed when daily added PAC particles were predeposited on the membrane surfaces. These results support the assumption that the membranes surface properties and PAC layer structure might have considerably influential factor on NOM removal. Moreover, it was concluded that the dominant removal mechanism of hybrid membrane system is adsorption of NOM within PAC layer rather than size exclusion of NOM by both of membrane pores. Transmembrane pressure (TMP) increases with PAC membrane systems support the view that PAC adsorption pretreatment will not prevent the development of membrane pressure; on the contrary, PAC particles themselves caused membrane fouling by blocking the entrance of pores of MF and UF membranes. Although all three source waters have similar HPI content, it appears that the PAC interaction with the entrance of membrane pores was responsible for offsetting the NOM fractional effects on membrane fouling for these source waters

Experimental investigation of trihalomethane formation and its modeling in drinking waters

This research developed models using multiple linear regression analysis for the prediction of trihalomethane formation in coagulated Istanbul drinking water sources. The power-law model (model 1), using only ΔUV272 as the designed parameter, proved the best model to describe the formation of trihalomethane. The other model (model 2), included pH, total organic carbon, chlorine dosages, ultraviolet absorbance at 254 nm (UV254), specific ultraviolet absorbance (SUVA) and differential absorbance at 272 nm (ΔUV272). The root-meansquare error (RMSE), normalization mean square error (NMSE), regression coefficient (R2) and index of agreement (IA) were used as statistical variables to evaluate the model performance. The better prediction results were obtained by model 1 for root-mean-square error, normalization mean square error, R2 and index of agreement as 9.14, 0.015, 0.95 and 0.99, respectively. © 2015, Chemical Publishing Co. All rights reserved