(715d) Effective Photocatalytic Oxidation of Antibiotics in Water: Effects of Carbon Support and Inorganic Anions

The presence of pharmaceutical compounds in wastewater has recently received high levels of attention as contaminants of concern in the environment. Sulfamethoxazole (SMX), a sulfonamide bacteriostatic antibiotic, is an antibiotic that has been extensively used for the treatment and prevention of both human and animal diseases. Since these antibiotics at low levels cause toxic effects on the aquatic ecosystem and human health and induce antibiotic-resistant pathogens, effective treatment methods for these antibiotics need to be developed. This study focused on the photocatalytic oxidation of SMX using the biochar-supported TiO₂ in presence of anions such as bicarbonate and nitrate. The simple sol-gel method for synthesis of biochar-supported TiO₂ showed tiny TiO₂ granules were well dispersed on the biochar with little agglomeration by the SEM, EDX and XRD analysis. The photolytic and photocatalytic degradation of SMX was carried out in aqueous suspension using the biochar supported TiO₂ (biochar-TiO₂) photocatalyst under UV light irradiation. The photolytic and photocatalytic oxidation using the biochar-TiO₂ under UV light irradiation showed similar removal of SMX. However, the photocatalytic oxidation resulted in higher mineralization of SMX (higher removal of TOC) indicating effective oxidation by the photocatalytic oxidation. Particularly this study investigated the effects of bicarbonate and nitrate on photocatalytic oxidation of SMX. The photocatalytic oxidation with 20-50 mM bicarbonate led to increase in removal of SMX and TOC (74% to 94% for SMX removal, 66% to 83% for TOC removal). This enhancement was thought to be mainly due to effective oxidation of SMX by bicarbonate radicals rather than hydroxyl radicals in presence of bicarbonate. Addition of 0.1-0.5 M nitrate to the photocatalytic oxidation also enhanced the removal of SMX and TOC by the factor of 1.2-1.5 because of additional nitrate as the electron acceptor to prevent quick recombination of electron holes and electron during the photocatalytic oxidation. The final products from the photocatalytic oxidation of SMX (i.e., sulfate, ammonium, nitrate) were detected from the treated samples while various oxidation products from the photocatalytic oxidation of SMX are being identified. The biotoxicity test exhibited negligible toxicity of the photocatalytically treated SMX with 20-50 mM bicarbonate. The oxygen uptake rate measurement using the activated sludge from the local wastewater treatment plant also indicated high biodegradation of the oxidation products generated by the photocatalytic oxidation. In overall, the photocatalytic oxidation using the biochar-supported TiO₂ under UV light irradiation would be effective treatment of SMX and other antibiotics in water when it will be combined with bicarbonate and nitrate as enhancers for photocatalytic oxidation.