Effects of catalytic ozonation catalyzed by TiO2 activated carbon and biochar on dissolved organic matter removal and disinfection by-product formations investigated by Orbitrap mass spectrometry

This study investigates the applicability of coconut-and coal-based activated carbon (ccAC and coAC) and eucalyptus biochar coated by titanium dioxide (TiO2-ccAC, TiO2-coAC, and TiO2-biochar, respectively) as a catalyst of catalytic ozonation. Molecular dissolved organic matter (DOM) removal and minimization of unknown disinfection by-products (DBPs) formation were investigated by unknown screening analysis with Orbitrap mass spectrometry. By ozonation with the catalyst, coAC could achieve the highest DOC removal of 1.5 mgC L-1 followed by ccAC at 1.2 mgC L-1 while other catalytic ozonation and O3 alone were similar with 1.0 mgC L-1 removal. The oxidation treatments removed high molecular weight molecules and formed oxidation by-products (OBPs) with low molecular weight highly oxidized (high carbon oxidation state (Cos), and saturated (negative (DBE-O)/C) character). Coating catalysts with TiO2 enhance removal of molecules with more oxidized and saturated compounds and formed a fewer number of OBPs. Catalytic ozonation before chlorination removed and produced organic precursors as increasing of trihalomethanes formation potential (THM-FP) and decreasing of intermediate chlorinated DBPs were observed. Almost half of CHO and CHOCl DBPs generated in the samples pre-oxidized by O-3 alone, O-3/coAC, or O-3/TiO2-coAC were similar, and some of the unique DBPs were also found by each treatment. Applications of catalytic ozonation in water treatment still need post treatments to ensure removals of OBP precursors before disinfection.

Automated summary

This study investigates the applicability of different types of activated carbon and biochar coated by titanium dioxide as catalysts for catalytic ozonation. The results show that catalytic ozonation can effectively remove dissolved organic matter and minimize the formation of unknown disinfection by-products. Coating the catalysts with titanium dioxide enhances the removal of more oxidized and saturated compounds.