Mineralization and biodegradability enhancement of natural organic matter by ozone–VUV in comparison with ozone, VUV, ozone–UV, and UV: Effects of pH and ozone dose

Abstract

The increase in mineralization and biodegradability of natural organic matter (NOM) by ozone–vacuum ultraviolet (VUV) in comparison with ozone, VUV, ozone–ultraviolet (UV), and UV were investigated. The effects of operating parameters including pH and ozone dose were evaluated. Results showed that the mineralization rate of dissolved organic carbon (DOC) provided by the processes tested was in the following order: ozone–VUV > VUV > ozone–UV > ozone > UV. Among three pH studied (7, 9, and 11), pH 7 provided the highest DOC mineralization rate and biodegradability increase. A synergistic effect was observed when combining ozone with UV or VUV at pH 7 and 9 but not at pH 11. The oxidized NOM samples were separated into six fractions based on polarity (hydrophobic/hydrophilic) and charge (acid/neutral/base) to reveal NOM characteristic changes. Ozone–VUV was effective in mineralizing hydrophobic neutral and acid fractions. The hydrophilic neutral fraction was a major NOM fraction after oxidation (39–87%) and was contributed to by the biodegradable DOC produced during oxidation. High performance size exclusion chromatography results revealed that the combination of UV or VUV with ozone was more effective in the decomposition of high molecular weight compounds than ozone alone.