Influence of chloride on the 185 nm advanced oxidation process

The use of 185 nm radiation from a conventional low pressure mercury lamp generates the hydroxyl radical (OH) from the photolysis of water and offers an advanced oxidation process (AOP) for water treatment that does not require chemical addition. However, the influence of the water matrix on the process differs substantially from that of other ultraviolet and ozone based processes. In particular chloride (Cl^-), and not water, absorbs the majority of 185 nm photons when [Cl^-]>20mgL^-1 and generates the chlorine atom radical (Cl) as a reactive species. Evidence suggests that when Cl^- is present, Cl and OH both contribute to contaminant degradation to varying extents. Using nonselective (carbamazepine) and selective (nitrobenzene) radical probes, as well as nonselective (t-butanol), and selective (acetone and acetate) radical scavengers, the influence of Cl^-, and therefore 185 nm AOP treatment efficiency, is observed to strongly depend on four independent second-order radical rate constants. Furthermore, ionic strength effects support the assumption that Cl is in equilibrium with the relatively nonreactive dichlorine radical anion ().