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

Purpose The treatment and management of gentamicin mycelial residue (GMR) is challenging due to the high residual antibiotic content in GMR. The objectives of this study were to investigate the viability of recycling GMR by co-composting with rice chaff, describe the dynamics of the physicochemical and biological parameters and the microbial community, and evaluate the maturity of the composting products. Methods The treatment and management of gentamicin mycelial residue (GMR) is challenging due to the high residual antibiotic content in GMR. Three 1-tonne piles of fresh GMR were composted with each treatment; the test treatments contained rice chaff, and the control treatment did not contain rice chaff. Dried GMR was prepared by drying fresh GMR. Composting was performed in cones with a diameter of 2 m and a height of 1.5 m using different ratios of fresh GMR to rice chaff (8:1 and 4:1) or in the absence of rice chaff (control). Results The optimal fresh GMR: rice chaff ratio (w/w) was 4:1. Characteristic temperature profiles consisting of a very brief mesophilic phase, a 4-57-day thermophilic phase (maximum of 50-70 degrees C) and a cooling phase (45-35 degrees C) after 58-73 days were observed. After 73 days of co-composting, 99.66% of gentamicin was degraded. All key parameters of the final products, such as the pH (8.12), EC (2.43 mS/cm), carbon/nitrogen ratio (8.6), germination index (96.06%) and crop growth indexes, met the national standards for compost maturity indicators. Compared with those of fungi, the number of OTUs, Chaol index and Shannon index of the bacteria in the T2 treatment clearly increased from 78, 105.14 and 0.97 to 149, 161 and 3.30, respectively, during the whole co-composting. A 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 responsible for the degradation of 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 of applying co-composting with rice chaff to achieve sustainable GMR management. [GRAPHICS] .