GENERATION OF RADICALS IN FERROUS-PERSULFATE SYSTEM USING KRCL EXCILAMP

Abstract

Generation of sulfate radical anion (SО4•–) and hydroxyl radical (•OH) in the ferrous-persulfate system (UV/PS/Fe2+), activated with KrCl excilamp (222 nm) radiation, was studied. To detect radicals and evaluate levels of their action, degradation experiments were conducted using the probe compounds, which trap the target radicals – terephtalic acid (TPA) and p-chlorobenzoic acid (pCBA). Deionized water (DW), natural water (NW) and wastewater (WW), containing a probe compound, were sequentially treated by direct UV, UV/PS and UV/PS/Fe2+ systems. The ferrous-persulfate system was shown to be the most efficient in terms of radical generation within the same water matrix: UV/PS/Fe2+ > UV/PS > UV. Comparing different water matrices, the lowest radical generation was observed in WW. Since TPA and pCBA were unsuitable compounds to assess the contributions of SО4•– and •OH by comparison of degradation degree with and without methanol and tert-buthanol, herbicide atrazine (ATZ) was taken as a model organic pollutant with comparable reaction rate constants with SО4•– and •OH. Scavenging experiments with ATZ and alcohols showed a major contribution of SO4•– during UV/PS/Fe2+ treatment of DW (79%) and NW (60%), whereas SO4•– and •OH contributed equally in WW. Direct UV irradiation (without persulfate and Fe2+) indicated the •OH production in WW, presumably, due to high photoreactivity of dissolved organic substance (DOM).