A comparative study of the effects of ozonation and TiO2-catalyzed ozonation on the selected chlorine disinfection by-product precursor content and structure

This study compares the effects of ozonation (0.4–3.0 mg O3/mg DOC) and TiO2-catalyzed ozonation — TiO2–O3 (0.4–3.0 mg O3/mg DOC; 1.0 mg TiO2/L) at pH 6 on the content and structure of natural organic matter (NOM) and trihalometane (THM) and haloacetonitrile (HAN) precursors in groundwater. The investigated groundwater from Northern Serbia is rich in NOM (9.85 mg/L DOC) which is mostly of hydrophobic character (65% fulvic acid and 14% humic acid fraction). It was found that the TiO2-catalyzed process, by favoring the radical mechanism of NOM oxidation, resulted in a more effective reduction in the content of total NOM (up to 18% DOC) compared to ozonation alone (up to 6% DOC). The use of TiO2 also resulted in an improvement of ozonation in terms of THM precursor content removal (up to 80%). On the other hand, the application of both oxidation treatments resulted in an increase in the HANFP compared to the raw water. NOM oxidation during ozonation and TiO2–O3 caused changes in their structure in the direction of an increased proportion of the hydrophilic fraction (up to 70%), which has the most reactive THM and HAN precursors, as well as the fraction with the highest content of their brominated species.

► The effects of ozonation and TiO2–O3 on the structure of NOM were investigated.
► TiO2–O3 improved NOM and THMFP reduction compared to ozonation alone.
► Both oxidation treatments lead to increases in the HANFP compared to the raw water.
► Ozonation and TiO2–O3 resulted in HAF oxidation, increasing the hydrophilic content.
► Hydrophilic fraction has the most reactive THM and HAN precursors after oxidation.