Rate of chloramine decay at pipe surfaces

摘要

The PSR was successfully applied to measure chlor-amine decay. In the presence of CI pipe, chloramine decay was three orders of magnitude faster than bulk decay. The observed reaction rate in CI pipe was first order with respect to chloramine, unlike the zero-order reaction found for free chlorine in previous work (DiGiano & Zhang, 2005). This difference was attributed to the slower reaction of chloramine than that of free chlorine, which therefore controls the reaction rate instead of Fe~(2+) in the corrosion scales. The rate of reaction at the CI pipe surface increased with decreasing pH. One possible explanation is that lower pH causes an increase in Fe~(2+) dissolution from corrosion scales with subsequent oxidation by chloramine.