Photocatalytic degradation of tetracyclines in liquid digestate: Optimization, kinetics and correlation studies.

• A photocatalytic process was used to degrade tetracyclines in biogas slurry. • TC, OTC and CTC removal reached 94.99%, 88.92%, and 95.52% under optimum conditions. • Adsorption of tetracyclines was increased by the concentration of biogas slurry. • Flocculation pretreatment can improve photocatalytic efficiency. • pH, total solid and chroma of biogas slurry significantly affect photocatalysis. The high concentration of antibiotics in liquid digestate makes it unviable for use as fertilizer on farmland. This study designed a system for antibiotic degradation and applied the photocatalytic process to degrade tetracyclines in liquid digestate. The effects of different operational variables (e.g., radiation source, TiO 2 concentration, photocatalytic time, temperature, and depth of Liquid digestate) on the removal of tetracyclines were analyzed and optimal operation conditions were obtained. The correlation between the physicochemical properties of liquid digestate and tetracyclines removal was also analyzed. The results indicate that a high pressure mercury lamp is effective for the photocatalysis of tetracyclines in liquid digestate. Tetracyclines removal increased with increasing TiO 2 concentration, photocatalytic time, and decreasing liquid digestate depth. However, the temperature of liquid digestate had little effect on the removal of tetracyclines. Under the high pressure mercury lamp, the removal of tetracycline, oxytetracycline, and chlortetracycline reached 94.99%, 88.92%, and 95.52%, respectively, under the optimum conditions (TiO 2 concentration of 1.0 g/L, liquid digestate depth of 20 mm, and photocatalytic time of 120 min). In addition, the tetracyclines concentration, pH, total solid, and chroma of liquid digestate all had significant effects on the photocatalytic process. Flocculation pretreatment can improve photocatalytic efficiency by reducing the chroma, pH, and TS of liquid digestate. Our findings show that photocatalysis is an effective method for removing antibiotics in liquid digestate and has the potential for application to pollutant removal. Furthermore, our results provide conditions for the popularization and application of apparatus for the degradation of antibiotics in liquid digestate. [ABSTRACT FROM AUTHOR]