Influence of oxidation on fulvic acids composition and biodegradability

• We studied the influence of different doses oxidants on changes in fulvic acids (FA).
• Biological activity occurred by mineralization of small and biotransformation of big molecules.
• Chlorine substituted into the FAs structure.
• Chlorine dioxide oxidized FA stronger than chlorine and they became more biodegradable.
• Ozonation is the most preferable process for pre-treatment of FAs before biofiltration.

Oxidation is well-known process of transforming natural organic matter during the treatment of drinking water. Chlorine, ozone, and chlorine dioxide are common oxidants used in water treatment technologies for this purpose. We studied the influence of different doses of these oxidants on by-products formation and changes in biodegradable dissolved organic carbon (BDOC) and molecular weight distribution (MWD) of fulvic acids (FA) with different BDOC content.Chlorination did not significantly change the MWD of FA and disinfection by-products formation. However, higher molecular weight compounds, than those in the initial FA, were formed. It could be a result of chlorine substitution into the FA structure. Chlorine dioxide oxidized FA stronger than chlorine. During ozonation of FA, we found the highest increase of BDOD due to the formation of a high amount of organic acids and aldehydes. FA molecules were transformed into a more biodegradable form. Ozonation is the most preferable process among those observed for pre-treatment of FA before biofiltration.