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.
Bibliographical noteFunding: This research was funded by The Deanship of Scientific Research at The Hashemite University, Ulster University’s VCRS Postgraduate Scholarship Scheme and SAFEWATER project sponsored by Global Challenges Research Fund (GCRF) UK Research and Innovation (SAFEWATER; EPSRC Grant Reference EP/P032427/1).
- Advanced oxidation processes