Theoretical Evaluation of UV Reactors in Series

A theoretical analysis is provided of the extent to which doses from ultraviolet (UV) reactors in series are additive. It is shown that UV reactors' reduction equivalent dose (RED) depends on the sensitivity of the microbe, the limits of which are the minimum and average of the dose distribution for infinitely sensitive and infinitely resistant microbes. For complete interbank mixing between two reactors in series, the additivity of RED is preserved. For systems where there is a negative correlation between dose paths, the RED is greater than or equal to twice that of a single reactor. The converse occurs for positive correlation. It is proven that when a single reactor is validated with a microbe whose sensitivity is at least twice that of the target microbe, it is assured that two identical UV reactors in series will deliver a RED at least two times that of the single reactor. (C) 2015 American Society of Civil Engineers.