Distribution and fate of antibiotics and their main metabolites in sludge stabilization technologies

Sewage sludge tends to accumulate emerging contaminants during wastewater treatment, with many pollutants persisting even after undergoing sludge stabilization treatments, posing potential environmental risks. Antibiotic contamination is of particular concern due to their high persistence and ability to promote the development of resistance genes. However, limited information is available regarding the behavior of antibiotic metabolites. In this study, seventeen antibiotics and metabolites of five therapeutic groups of critically and highly important antibiotics were monitored in wastewater and sludges from fifteen wastewater treatment plants (WWTPs) with five different sludge stabilization treatments: anaerobic digestion, aerobic digestion, dehydration, composting, and lagooning. Results demonstrated that the distribution ratio of metabolites and parent compounds in influent wastewater was correlated with their excretion rates, reflecting pharmaceutical consumption as their primary source to WWTPs. Fluoroquinolone and sulfonamide antibiotics were predominant in influent wastewater, while macrolide antibiotics were more prevalent in primary sludge, likely due to their higher hydrophobicity, which results in greater retention in sludge. Parent compounds dominated over metabolites in sewage sludge, with composting plants showing the highest removal efficiency and highest metabolization among all sludge stabilization technologies studied. Tetracyclines were not detected in any of the sludge samples analyzed and macrolides resulted in the most persistent antibiotics in treated sludges. Results showed low environmental risks associated with the reuse of treated sludge as an organic amendment in agriculture.