| Abstract
| - Both low- and medium-pressure Hg lamps (LP and MP,respectively) were used as ultraviolet light (UV) sources todestroy N-nitrosodimethylamine in a synthetic “natural”water. The lamp performances were directly compared viathe UV fluence-based rate constants, which demonstratesthat LP and MP have virtually identical photonic efficiencies(fluence-based rate constants of 2.29E-3 and 2.35E-3 cm2/mJ, respectively). This indicates that the quantum yieldfor NDMA photolysis is independent of wavelength in theUVC region: a value of 0.30 mol/einstein is found at pH8.1. Addition of 100 mg/L of H2O2 leads to a 30% increasein the LP fluence-based rate constant but does notalter the MP rate constant, likely due to the tradeoffbetween light screening by H2O2 and additional radicalbased degradation. However, in terms of the time-basedrate constant, this level of H2O2 slightly enhances the LPperformance but hinders the MP performance, suggestingthat H2O2 is of little or no economic benefit for NDMAremoval by UV. All these effects are explained by modelingthe photochemistry according to standard equations.The model predicts that H2O2 may enhance NDMA removalfor short optical path lengths but that light-screening byH2O2 may decrease the removal rates for optical path lengthstypical of those found in UV reactors.
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