Inuence of major anions on the 185 nm advanced oxidation process - Sulphate, bicarbonate, and chloride

Abstract

The 185 nm wavelength radiation generated by the conventional low pressure mercury lamp forms the basis of an advanced oxidation process (AOP) that does not require chemical addition. The photolysis of water by 185 nm photons generates the hydroxyl radical (OH) used to degrade trace organic contaminants. While AOPs in general suffer decreased efficiency in direct proportion to the concentrations of dissolved organic matter (DOM) and alkalinity (HCO3−/CO32−), acting as OH scavengers, such solutes impose an additional parasitic effect on the 185 nm AOP as absorbers of photons. Furthermore, the major inorganic anions sulphate (▪) and chloride (Cl−) also absorb at 185 nm to generate the highly reactive sulphate (▪) and chlorine (Cl) radicals. Like OH, ▪ and Cl. are also scavenged by DOM and HCO3−/CO32−. Using carbamazepine as a radical probe, and t-butanol or Suwannee River isolate as model DOM, the relative reactivity of these radicals with both DOM and HCO3− was found consistent with the order ▪. Experimental evidence suggests some interconversion between these radicals. The 185 nm AOP treatment efficiency thus depends strongly on the anionic composition of the water matrix, as well as on the relative reactivities of the target contaminant, DOM, and HCO3− with the three radicals OH, Cl., and ▪. Changes in any of these parameters may result in substantial differences in treatment efficiency.