摘要：

Ultraviolet (UV) disinfection is being increasingly used in drinking water treatment. It is important to understand how its application to different types of water may influence finished water quality, particularly as anthropogenic activity continues to impact the quality of source waters. The objective of this study was to evaluate the effect of inorganic precursors on the formation of regulated and unregulated disinfection byproducts (DBPs) during UV irradiation of surface waters when combined with chlorination or chloramination. Samples were collected from three drinking water utilities supplied by source waters with varying organic and inorganic precursor content. The filtered samples were treated in the laboratory with a range of UV doses delivered from low pressure (LP, UV output at 253.7nm) and medium pressure (MP, polychromatic UV output 200–400nm) mercury lamps followed by chlorination or chloramination, in the presence and absence of additional bromide and nitrate. The regulated trihalomethanes and haloacetic acids were not affected by UV pretreatment at disinfection doses (40–186mJ/cm2). With higher doses (1000mJ/cm2), trihalomethane formation was increased 30–40%. While most effects on DBPs were only observed with doses much higher than typically used for UV disinfection, there were some effects on unregulated DBPs at lower doses. In nitrate-spiked samples (1–10mgN/L), chloropicrin formation doubled and increased three- to six-fold with 40mJ/cm2 MP UV followed by chloramination and chlorination, respectively. Bromopicrin formation was increased in samples containing bromide (0.5–1mg/L) and nitrate (1–10mgN/L) when pretreated with LP or MP UV (30–60% with 40mJ/cm2 LP UV and four- to ten-fold increase with 40mJ/cm2 MP UV, after subsequent chlorination). The formation of cyanogen chloride doubled and increased three-fold with MP UV doses of 186 and 1000mJ/cm2, respectively, when followed by chloramination in nitrate-spiked samples but remained below the World Health Organization guideline value of 70μg/L in all cases. MP UV and high LP UV doses (1000mJ/cm2) increased chloral hydrate formation after subsequent chlorination (20–40% increase for 40mJ/cm2 MP UV). These results indicate the importance of bench-testing DBP implications of UV applications in combination with post-disinfectants as part of the engineering assessment of a UV-chlorine/chloramine multi-barrier disinfection design for drinking water treatment.

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