Simultaneous Removal of Tetracycline and Cu(II) in Hybrid Wastewater through Formic-Acid-Assisted TiO2 Photocatalysis

In this study, a common refractory aquaculture hybrid wastewater containing copper and tetracycline (TC) was treated to simultaneously remove such pollutants through a formic-acid-assisted photocatalysis process with TiO2 as the photocatalyst. The results show that pure aqueous TC can be completely photodecomposed by TiO2, although the removal rate of pure Cu ions through photocatalysis without the addition of a scavenger can be neglected. For simultaneously photodegrading TC–Cu­(II) hybrid wastewater, the TC degradation rate is accelerated, whereas the Cu­(II) removal rate remains at 20% through adsorption. TC cannot promote the photoreduction of Cu­(II) as a sacrificial agent, and its intermediate products form a stable complex with Cu­(II), hindering further reduction. The addition of formic acid effectively releases Cu ions from the complex as a pH regulator and enhances the photocatalysis process as a hole scavenger. Through the addition of formic acid after complete TC photooxidation, the final chemical oxygen demand (COD) and Cu concentration were only 8 and 0.4 mg/L, respectively. This study provides a simple and promising method for simultaneously treating TC–Cu­(II) hybrid wastewater using formic-acid-assisted TiO2 photocatalysis.