Comparison of ozonation and AOPs combined with biodegradation for removal of THM precursors in treated sewage effluents

The efficiency of ozonation (O₃) and advanced oxidation processes (AOPs) such as O₃/UV, O₃/H₂O₂, H₂O₂/UV and O₃/H₂O₂/UV was examined for removal of trihalomethane (THM) precursors in treated sewage effluents. A low-pressure mercury (Hg) lamp (maximum wavelength 253.7 nm; intensity 2.6 × 10⁻⁶ Einstein s⁻¹) was employed for AOPs using ultraviolet light. The efficiency of the processes employed was examined by both direct mineralization of target compounds and the formation of biodegradable compounds, based on the removal of dissolved organic carbon (DOC), UV absorbance at 260 nm (UV260), and THM formation potential (THMFP). The contribution of ozonation was relatively small for mineralization of DOC, but was larger for the increase in biodegradability of residual DOC. On the other hand, AOPs were effective for both mineralization and increase in biodegradability. A longer reaction time with AOPs resulted to an increase in mineralization but not to an increase in biodegradable components possibly because the biodegradable components were also decomposed by AOPs. The removal of UV260 was obtained by chemical/photolytic processes and not by biodegradation. The rate of THMFP removal by ozonation, AOPs, and biodegradation was higher than that of DOC removal.