Effects of Pilot-Scale Co-Composting of Gentamicin Mycelial Residue with Rice Chaff on Gentamicin Degradation, Compost Maturity and Microbial Community Dynamics

Purpose: It is challenging to treat and manage gentamicin mycelial residue (GMR) due to the high residual antibiotic content in GMR. The objective of this study is aimed to investigate the viability of recycling GMR by co-composting with rice chaff, describe the dynamics of the physicochemical and biology parameters and microbial community, and evaluate the maturity of the compost products. Methods: The co-composting process applied was a pilot-scale composting process under the conditions found outside the laboratory. Three 1-tonne piles of fresh GMR were composted in each treatment; test treatment contained rich chaff and the control did not. Dried GMR was made by drying fresh GMR. Three compost treatments were as follows: (1) no rice chaff, 8:1 weight/weight fresh GMR-to-dried GMR (CK); (2) 8:1 weight/weight fresh GMR-to-rice chaff (T1); and (3) 4:1 weight/weight fresh GMR-to-rice chaff (T2). The raw materials were made into three compost cones of 2 m diameter and 1.5 m height. Results: The optimal fresh GMR:rice chaff ratio (w/w) was 4:1. Over 99% of gentamicin was degraded after 73 days of co-composting. The key parameters of the final products, such as the pH, C/N ratio, germination index and crop growth indexes, all met the national standards for compost maturity indicators. Compared with those of fungi, the abundance and diversity of bacteria obviously increased during co-composting. Canonical correlation analysis (CCA) revealed that the bacterial community dynamics were closely correlated with the amount of residual gentamicin. Micromonospora and Enterococcus may have been the key microorganisms degrading the gentamicin. Conclusion: The addition of rice chaff improved the decomposition of gentamicin residue in the GMR and made the GMR usable in fertilizer; this result could help antibiotic production factories recycle more of their waste products. The results provide new insight into the potential for co-composting with rice chaff to achieve sustainable GMR management.