Comparison of UV and UV/H₂O₂ treatments using excilamps for removal of monochlorophenols in the molecular and anionic form

Abstract

The efficiency of UV/H₂O₂ treatment using KrCl (222 nm) and XeBr (282 nm) excilamps was examined for removal of 2-chlorophenol (2-CP) and 4-chlorophenol (4-CP) from aqueous solution in the molecular form (pH 2 and un-adjusted pH) and anionic form (at pH 11). UV/H₂O₂ treatment of 2- or 4-CP was initially carried out at un-adjusted pH with varying molar ratios of chlorophenol and H₂O₂. The para-chlorobenzoic acid was used as a hydroxyl radical (•OH) probe compound. UV/H₂O₂ treatment of 2- and 4-CP with a molar ratio of 1:25 at ambient pH and a fluence of 4.1 J/cm² provided a significant decrease in chemical oxygen demand (COD). Under these conditions, the •OH exposure was found to increase from 0.5 × 10⁻¹¹ and 0.4 × 10⁻¹¹ to 1.8 × 10⁻¹¹ and 1.3 × 10⁻¹¹ M min for KrCl and XeBr excilamp, respectively. Compared with direct UV photolysis, the pseudo-first-order fluence-based rate constants of 2- and 4-CP degradation in UV/H₂O₂ process at a molar ratio of 1:25 were significantly higher for molecular 2-CP and 4-CP in the anionic form using both excilamps. Detailed information on UV fluence and/or the exposure to •OH radicals is proposed to accurately compare studies reporting the effectiveness of AOPs based on excilamps.

Keywords:

• Chlorophenol
• degradation
• excilamp
• hydrogen peroxide

Acknowledgments

The authors thank Dr. Maria Gómez (Murcia University, Spain) for help in analytical procedure issues and Prof. Nick Christofi (Edinburgh Napier University, UK) for discussion on the manuscript.