Analysis of Trihalomethanes Formed During Drinking Water Chlorination

Summary

Analyses of trihalomethanes (mainly chloroform) were performed in connection with chlorination of drinking water. A typical Norwegian water source with relatively high content of humic constituents was treated to reduce the organics that cause trihalomethanes to be formed in the chlorination process. A gas chromatograph with an electron capture detector (GC-ECD) was used in the analyses. The workup of the trihalomethanes was done through a liquid-liquid extraction of the water samples with n-pentane. Chlorination of the raw water with 2mg Cl₂/l gave an average of 37.3μg CHCl₃/l. Raw water from the same source was then treated in a filtration pilot plant. A decrease in the chlorine demand of about 50% was observed. Reducing the amount of chlorine accordingly, gave a decrease in CHC1₃ formation of 50% on the filtered water. The effluent from the pilot plant chlorinated with a constant dose of chlorine showed a linear correlation between the amount of CHCl₃ formed and UV-extinction. Experimental results are also presented showing the influence of variation in pH, temperature, chlorine dosage and humic and bromine content on the production of trihalomethanes.