Treatment of Wastewater Using a Magnetically Recoverable Ag-Based Photocatalyst

A novel catalyst, composed of silver phosphate (Ag3PO4) deposited on a magnetic material containing titanium dioxide (TiO2) and ferromagnetite (Fe3O4), was synthesized and tested with wastewater from the maintenance system of a swimming pool and from the secondary effluent of a wastewater treatment plant (WWTP). The magnetic material Ag3PO4@1-TiO2-Fe3O4 presented a slightly lower photoactivity than bare Ag3PO4 but was able to remove over 64% COD from the secondary effluent of a WWTP and over 75% organic UV filters from a swimming pool wastewater. The material was easily recovered from the treated water with a magnet and could be reused at least four times. The efficiency loss after five reuses was 15%. The dissolution of silver after the photocatalytic reaction was over 80 mg·L−1 for bare Ag3PO4 and less than 500 μg·L−1 for the magnetic composites. The magnetic support prevents the dissolution of silver. The materials that contained Ag3PO4 showed antibacterial properties under dark conditions. The photocatalytic efficiency of Ag3PO4 and commercial TiO2 was similar under sunlight, both for the removal of UV filters at µg·L−1 concentrations from swimming pool wastewater, and for the removal of mild COD loads from a WWTP effluent (initial COD: 110 mg·L−1).