Low molecular weight oxidation by-products produced during catalytic ozonation with ferric hydroxide of NOM fractions isolated from filtrated water

Natural organic matter(NOM) in a filtered river water from a water treatment plant was isolated and fractionated into six types of fractions. The aim of the work is to investigate the formation of the low molecular weight(LMW) oxidation by-products(i.e. aldehydes, ketones and ketoacids) after ferric hydroxide-catalyzed ozonation of individual NOM fractions. Results showed that catalytic ozonation could improve the reduction of the dissolved organic matter(DOC) and specific UV absorbance(SUVA) at 254 nm compared with ozonation alone. However, catalytic ozonation with ferric hydroxide could not produce less LMW oxidation by-products than ozonation. Hydrophobic neutral(HON) produced much higher yields of the LMW oxidation by-products than other fractions both during catalytic ozonation and ozonation alone, while the basic NOM fractions formed relatively lower productions of these by-products. Like the case of ozonation alone, the predominant contributors for the yields of aldehydes and ketoacids formed in catalytic ozonation were formaldehyde and pyruvic acid, respectively. Among these NOM fractions, HON produced the highest yields of the formaldehyde and pyruvic acid after catalytic ozonation. The yield of formaldehyde from HON was up to 71.6% of the total aldehydes and ketones, and the pyruvic acid concentration of HON was 78.6 μg/mg after catalytic ozonation. In addition, NOM fractions became more biodegradable after catalytic ozonation, because the percent of total LMW by-products carbon in the final DOC after catalytic ozonation was higher than ozonation alone.