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