Antibiotic Degradation During Thermophilic Composting

Residual antibiotics in land-applied manure and biosolids present a potential threat to public and ecological health. It remains important to determine antibiotic degradation efficiencies for manure and biosolids waste management practices and to identify conditions that enhance antibiotic degradation. The fates of the antibiotics florfenicol, sulfadimethoxine, sulfamethazine, and tylosin were studied during pilot-scale static pile thermophilic composting, and the effects of temperature and feedstock particles on antibiotic degradation rates were tested. The antibiotics were spiked into dairy manure solids and wastewater biosolids, and treatments included aerated and non-aerated manure and biosolids/wood-product (1:3 v/v) composting. Results showed no significant differences between aerated and non-aerated treatments; on average, ≥85, ≥93, and ≥95 % antibiotic degradation was observed after 7, 14, and 21 days of composting. Greater antibiotic degradation was observed in manure compost compared to biosolids compost for florfenicol (7, 14, 21, 28 days) and tylosin (14, 28 days); however, there was no significant difference for sulfadimethoxine and sulfamethazine. Peak temperatures were 66–73, and ≥55 °C was maintained for 6–7 days in the biosolids compost and 17–20 days in the manure compost. Bench-scale experiments conducted at 25, 55, and 60 °C showed that lower temperature decreased degradation of the sulfonamides and tylosin in both feedstocks and florfenicol in the biosolids. The presence of compost particles increased antibiotic degradation, with time to 50 % degradation ≤2 days in the presence of solids (60 °C) compared to no degradation in their absence. These results indicate that thermophilic composting effectively degrades parent antibiotic compounds in manure and biosolids.