UV 222 nm Emission from KrCl* Excimer Lamps Greatly Improves Advanced Oxidation Performance in Water Treatment

KrCl* excimer lamps emitting at 222 nm hold potential for enhancing ultraviolet (UV)-based advanced oxidation efficiency. Experiments were conducted in both ultrapure water and groundwater comparing low-pressure UV (LPUV) and KrCl* excimer lamps, with two different radical promoters [hydrogen peroxide (H2O2) and nitrate (NO3–)]. Compared to that of conventional LPUV/H2O2, the steady-state hydroxyl radical (•OH) concentration achieved in the KrCl*/NO3– UV/AOP was 13.1 times greater while that for the KrCl*/H2O2 process was 9.4 times greater in ultrapure water; the values in groundwater were 7.3 and 3.7 times greater, respectively, all using a standard single probe compound decay method as a proxy for •OH radical generation. This work identified several research gaps that must be addressed to facilitate adoption of KrCl* for UV/AOP, including development of methods for comparing UV/AOPs that utilize different UV radiation sources and radical promoters, a need to acquire more information about direct photolysis quantum yields at 222 nm for contaminants of concern, and the impact of the background water matrix constituents on radical promotion or formation of any byproducts, especially in the presence of NO3– as a radical promoter.