Effects of in situ ozonation on structural change of soil organic matter

Four different soils were collected from the field and oxidized using gaseous ozone. The soil organic matter (SOM) was extracted from test soils and analyzed to examine the structural changes of SOM due to the chemical oxidation. Various characteristics of the water-soluble SOM, such as the pH, dissolved organic carbon (DOC), specific UV absorbance (SUVA), carboxylic acidity, average molecular weight, and structure, were strongly affected by SOM content and ozonation time. The pH values of the extracts were found to decrease with longer ozonation times, and this was due to the formation of carboxylic acids originating from the oxidation of the SOM. The DOC concentration and SUVA increased with a greater oxidation time due to the increased dissolution of humic or fulvic acids into the extracts. As well, the ozonation of SOM enhanced the dissolution of hydrophilic fraction of SOM into the soil water phase. Hence, the biologically degradable fraction of the water-soluble SOM increased proportional with ozone treatment due to an increase in its hydrophilic content.