Removal of natural organic matter (NOM) by ozone and ultraviolet based advanced oxidation processes: Development of NOM fractionation technique, process performances, and bromate formation

Natural organic matter (NOM) is a complex mixture of organic compounds. In this dissertation, the removal of NOM by advanced oxidation processes (AOPs) including ozone-vacuum ultraviolet (VUV), ozone, VUV, ozone-ultraviolet (UV), and UV was investigated. A new NOM fractionation technique was developed in order to elucidate the change of NOM composition under the treatment processes. NOM was separated into six fractions based on polarity (hydrophobic/hydrophilic) and charge (acid/neutral/base). The new technique provided reliable results within 6 hours compared to 24 hours by traditional procedures.;The process performances on NOM removal was evaluated based on the mineralization of dissolved organic carbon (DOC), reduction of UV absorbance at wavelength 254 nm (UV254) (unsaturated and aromatic carbon contents), and biodegradability enhancement. The effects of operating parameters including pH and ozone dose were examined. Results showed that DOC mineralization rate was in the following order: ozone-VUV > VUV > ozone-UV > ozone > UV. Ozone-VUV removed up to 71% of DOC while ozone and ozone-UV mineralized only 7% and 28% of DOC, respectively. Approximately, 90% UV254 reduction and 68% increase of biodegradability were achieved by ozone-VUV process. Among three pH studied (7, 9, and 11), pH 7 provided the highest DOC mineralization rate and biodegradability enhancement. The results of NOM fractionation showed that ozone-VUV was effective in mineralizing hydrophobic neutral and acid fractions. Hydrophilic neutral fraction was a major NOM fraction after oxidation (39-87%) and was contributed by biodegradable DOC produced during the oxidation.;The effect of AOPs on bromate formation, a common carcinogenic ozonation byproduct, was also investigated. Bromate formation during the ozone-VUV process was up to 4 and 6 times less than ozone and ozone-UV, respectively. This was because VUV irradiation, which was applied simultaneously with ozone, reduced bromate formation. Ozone dosage was found to have the most effect on bromate formation in the ozone-VUV process. Approximately 64% and 213% increases of bromate concentration were observed when the ozone dosage was increased from 1 to 2 and 4 mg O3/mg C with VUV power of 120 W at pH 7. Bromate formation also increased as VUV power and pH increased.