Residual antibiotics in land-applied manure and biosolids present a potential threat to public and ecological health, so it is important to determine antibiotic removal efficiencies for manure and biosolids waste management practices and to identify conditions that enhance antibiotic degradation.
What we did
Loss of the antibiotics florfenicol, sulfadimethoxine, sulfamethazine, and tylosin was studied during pilot-scale static pile thermophilic composting and the effects of temperature and feedstock particles on antibiotic removal 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.
Figure 1. Applying antibiotic solution to biosolids
What have we learned
Results showed no significant differences between aerated and non-aerated treatments; on average ≥85%, ≥93%, and ≥95% antibiotic reduction was observed after 7, 14, and 21 d of composting. Greater antibiotic reduction was observed in manure compost compared to biosolids compost for florfenicol (7, 14, 21, 28 d) and tylosin (7, 14, 28 d); however, there was no significant difference for sulfadimethoxine and sulfamethazine. Peak temperatures were 66-73°C, and ≥55°C was maintained for 6-7 d in the biosolids compost and 17-20 d in the manure compost.
Bench-scale experiments conducted at 25, 55, and 60°C showed that lower temperature decreased removal of the sulfonamides and tylosin in both feedstocks and florfenicol in the biosolids. The presence of compost particles increased antibiotic loss, with time to 50% dissipation ≤ 2 d in the presence of solids (60°C), compared to no degradation in their absence. These results indicate that thermophilic composting effectively reduces residual antibiotics in manure and biosolids.
Figure 2. Mixing biosolids and wood shavings
Figure 3. Mixing biosolids and wood shavings.
A. Bary*, S.M. Mitchell*, J.L. Ullman**, C.G. Cogger*, A.L. Teel*, R.J. Watts*
Washington State University*, University of Florida**.
Andy Bary, firstname.lastname@example.org
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Figure 4. Compost bins