Effects of different vermicomposting process with cattle manure in the removal of sulfamethoxazole and trimethoprim antibiotics

This study aimed to investigate the effect of vermicomposting process in removal of sulfamethoxazole (SMX) and trimethoprim (TMP) antibiotics in cattle manure. In this experimental study, vermicomposting process was performed in 6 reactors on a pilot scale. The cattle manure (3.5 kg) and Eisenia foetida worms (120 g) were added to each reactor. Sulfamethoxazole and trimethoprim antibiotics were added to reactors in four different concentrations of 10, 20, 50, and 100 mg/kg and two reactors were control free-worm with antibiotic and free antibiotic. Vermicomposting quality tests, including pH, electric conductivity (EC), total and volatile solids (VS), ash content, C/N, and potassium (K) were performed during the vermicomposting process for 8 weeks. Antibiotics concentration was analyzed using a high-performance chromatography (HPLC), and toxicity assessment of the final product was evaluated by germination index (GI) test. The results showed that there was a decrease in total solid, K and C/N and an increase in pH, EC, VS, and ash content parameters. Moreover, investigations showed a significant reduction in antibiotic concentrations at the end of the process. Antibiotics changes during the vermicomposting process showed that SMX had a faster removal rate compared to TMP and reached ≥ 99.99% at the end of the fourth week. In reactors with lower antibiotic concentrations, a faster removal rate was observed. The biodegradation of antibiotics follows first-order kinetics. GI toxicity assessment shows that this index reached 90% at the end of the process. Finally, it seems that vermicomposting is an effective method in reducing antibiotics in cattle manure.