Effects of added thermally treated penicillin fermentation residues on the quality and safety of composts.

Thermal treatment and composting are effective methods of degrading antibiotics and organic matter in penicillin fermentation residues (PFR), respectively. However, the composting efficiency and environmental safety of thermally treated PFR (HT-PFR) remain unclear. In this study, HT-PFR was composted with cattle manure and maize straw at ratios of 0:1:1 (CK), 1.5:1:1 (T1), and 5:1:1 (T2). Changes in physicochemical properties, seed germination index (GI), and microbial antibiotic resistance genes (ARGs) were determined. Addition of HT-PFR significantly reduced the C:N ratio of each compost (P < 0.05) and prolonged the thermophilic stage. The GI of CK and T1 composts increased during processing, whereas that of T2 compost remained low. The PO43- concentrations of T1 and T2 composts were 6.3- and 11.1-fold higher than that of CK, respectively. HT-PFR contained relatively small amounts of mineral elements, and composting it with cattle manure and maize straw provided balanced nutrients for plant growth. After 52 days of composting, most ARGs of the microflora were reduced to low levels, but blaTEM increased significantly in T2 compost. Overall, composting HT-PFR at up to 42% of a mix containing equal parts of cattle manure and wheat straw is an environmentally safe and effective way of transforming it into organic fertilizer.