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

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, TiO2 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 TiO2 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 (TiO2 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.