Abstract
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 TiO2-based advanced oxidation processes (AOPs) in a custom-built stirred tank reactor. The combinations of H2O2, O3, and immobilized TiO2 under either dark or UVA irradiation conditions were systematically evaluated—namely TiO2/dark, O3/dark (ozonation), H2O2/dark (peroxidation), TiO2/UVA (photocatalysis), O3/UVA (Ozone photolysis), H2O2/UVA (photo-peroxidation), O3/TiO2/dark (catalytic ozonation), O3/TiO2/UVA (photocatalytic ozonation), H2O2/TiO2/dark, H2O2/TiO2/UVA, H2O2/O3/dark (peroxonation), H2O2/O3/UVA (photo-peroxonation), H2O2/O3/TiO2/dark (catalytic peroxonation), and H2O2/O3/TiO2/UVA (photocatalytic peroxonation). It was found that combining different treatment methods with UVA irradiation dramatically enhanced the organic mineralization efficiency. The optimum TiO2 loading in this study was observed to be 0.96 mg/cm2 with the highest TOC removal (54%) achieved using photocatalytic peroxonation under optimal conditions (0.96 mg TiO2/cm2, 25 mg O3/min, and 0.7 H2O2/O3 molar ratio). In peroxonation and photo-peroxonation, the optimal H2O2/O3 molar ratio was identified to be a critical efficiency parameter maximizing the production of reactive radical species. Increasing ozone flow rate or H2O2 dosage was observed to cause an efficiency inhibition effect. This lab-based study demonstrates the potential for combined TiO2-AOP treatments to significantly reduce the organic fraction of real GW, offering potential for the development of low-cost systems permitting safe GW reuse.
Highlights
Global water resources are under increasing pressure due to rising demand caused by climate change [1], urbanization, and the growing world population [2]
GW was stirred for three hours under different conditions to examine the total organic carbon (TOC) removal by aeration alone, direct photolysis (UVA with and without aeration), and adsorption of organics onto the TiO2 coated films in the dark
The TOC reduction reached a maximum of 3%, with results implemented on the related figures throughout the paper
Summary
Global water resources are under increasing pressure due to rising demand caused by climate change [1], urbanization, and the growing world population [2]. In order to tackle those challenges, there is a considerable interest in the diversification of water sources, with the use of reclaimed greywater (GW) highlighted as a crucial potential water source [3]. Reclaiming GW could meet the needs of up to 75%. Of household water consumption [5]. GW will reduce household demand for freshwater [6], but will reduce the volume of. Given the pressure on freshwater resources in developing countries, and the need to control pollution of water bodies, where around 80% of untreated sewage is discharged to [8], considering options to treat and reclaim GW offer significant promise
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