| Summary: | In keeping with the circular economy approach, reclaiming greywater (GW) is considered a sustainable approach to local reuse of wastewater and a viable option to reduce household demand for freshwater. This study investigated the mineralization of total organic carbon (TOC) in GW using TiO<sub>2</sub>-based advanced oxidation processes (AOPs) in a custom-built stirred tank reactor. The combinations of H<sub>2</sub>O<sub>2</sub>, O<sub>3</sub>, and immobilized TiO<sub>2</sub> under either dark or UVA irradiation conditions were systematically evaluated—namely TiO<sub>2</sub>/dark, O<sub>3</sub>/dark (ozonation), H<sub>2</sub>O<sub>2</sub>/dark (peroxidation), TiO<sub>2</sub>/UVA (photocatalysis), O<sub>3</sub>/UVA (Ozone photolysis), H<sub>2</sub>O<sub>2</sub>/UVA (photo-peroxidation), O<sub>3</sub>/TiO<sub>2</sub>/dark (catalytic ozonation), O<sub>3</sub>/TiO<sub>2</sub>/UVA (photocatalytic ozonation), H<sub>2</sub>O<sub>2</sub>/TiO<sub>2</sub>/dark, H<sub>2</sub>O<sub>2</sub>/TiO<sub>2</sub>/UVA, H<sub>2</sub>O<sub>2</sub>/O<sub>3</sub>/dark (peroxonation), H<sub>2</sub>O<sub>2</sub>/O<sub>3</sub>/UVA (photo-peroxonation), H<sub>2</sub>O<sub>2</sub>/O<sub>3</sub>/TiO<sub>2</sub>/dark (catalytic peroxonation), and H<sub>2</sub>O<sub>2</sub>/O<sub>3</sub>/TiO<sub>2</sub>/UVA (photocatalytic peroxonation). It was found that combining different treatment methods with UVA irradiation dramatically enhanced the organic mineralization efficiency. The optimum TiO<sub>2</sub> loading in this study was observed to be 0.96 mg/cm<sup>2</sup> with the highest TOC removal (54%) achieved using photocatalytic peroxonation under optimal conditions (0.96 mg TiO<sub>2</sub>/cm<sup>2</sup>, 25 mg O<sub>3</sub>/min, and 0.7 H<sub>2</sub>O<sub>2</sub>/O<sub>3</sub> molar ratio). In peroxonation and photo-peroxonation, the optimal H<sub>2</sub>O<sub>2</sub>/O<sub>3</sub> molar ratio was identified to be a critical efficiency parameter maximizing the production of reactive radical species. Increasing ozone flow rate or H<sub>2</sub>O<sub>2</sub> dosage was observed to cause an efficiency inhibition effect. This lab-based study demonstrates the potential for combined TiO<sub>2</sub>-AOP treatments to significantly reduce the organic fraction of real GW, offering potential for the development of low-cost systems permitting safe GW reuse.
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