Ultraviolet photooxidation for the biodegradability enhancement of airborne o-xylene

Abstract

Ultraviolet (UV) photolysis was evaluated as a technique to convert recalcitrant aromatic volatile organic compounds (VOCs) into more biodegradable compounds. o-Xylene was investigated as the model compound due to its low biodegradability and low water solubility. o-Xylene contaminated gaseous streams with inlet loadings of up to 2700 g·m–3·h–1 were passed through an annular photoreactor equipped with a UV source emitting light at 254 nm and 185 nm wavelengths. Ultraviolet photolysis effectively degraded o-xylene at a maximum removal rate of about 700 g·m–3·h–1, with the principle oxidizing species being hydroxyl radical. Of the total o-xylene removed, measured as total organic carbon (TOC) or chemical oxygen demand (COD), between 30% and 50% was converted to water-soluble and more biodegradable intermediates. The biodegradability of the photolysis intermediates was comparable to that of methyl ethyl ketone (MEK), which is 2–10 times more biodegradable than o-xylene. These results show that the use of UV photolysis is a promising and effective pretreatment technique for enhancing the biodegradability of recalcitrant organic compounds such as aromatics. Key words: VOC, o-xylene, photolysis, biodegradation, air treatment, biofiltration, ozone, hydrogen peroxide.