The Effect of Operating Strategies on the Anaerobic Digestion of Gentamicin Mycelial Residues: Insights into the Enhancement of Methane Production and Attenuation of Gentamicin Resistance

Abstract

Anaerobic digestion (AD) has been widely employed for converting various biowastes into renewable energy. However, AD of gentamicin mycelial residues (GMRs, a byproduct of gentamicin production) is limited by ammonia inhibition and antimicrobial resistance risk. Compared to mesophilic AD (MMAD) of GMRs, this study looked into three semicontinuous AD processes, i.e., codigestion with wheat straw, thermophilic digestion (TAcoD), and AD at shortened retention time (RT). Results showed that a stable and safe AD could be achieved under suitable operating conditions. Co-digestion could effectively mitigate the adverse effect of ammonia inhibition. The methane production increased by 35.86% in TAcoD compared to that in MMAD and 43.99% of hazardous waste was reduced in TAcoD. Concerning the antimicrobial resistance of AD system, gentamicin was degraded efficiently and the degradation process was not involved in the expression of antibiotic resistance genes (ARGs) related to modifying enzyme. Effective removal of ARGs under three operating strategies was associated with a higher reduction in bacterial abundance of potential hosts. In addition, the changes in the relevant proteins for transformation and conjugation as predicted by PICRUSt suggested that thermophilic condition and shorter RT were conducive to the reduction of the dissemination risks of ARGs.

Optimizing anaerobic digestion: Benefits of mild temperature transition from thermophilic to mesophilic conditions

“…The principal coordinates analysis (PCoA), microbial biodiversity, and redundancy analysis (RDA) of the samples were implemented using the R Vegan package. The candidate biomarkers among the different phases were identified by linear discriminant analysis effect size (LEfSe) analysis [ 2 ]. A nonparametric factorial Kruskal–Wallis sum-rank test was performed with a significance level of p < 0.05, and the threshold value of the logarithmic linear discriminant analysis (LDA) score was 2.0 [ 29 ].…”

“…Microbially driven anaerobic digestion (AD) is a long-established technology adopted for methane (CH 4 ) production from a variety of organic waste types, including waste-activated sludge (WAS), food waste (FW), and livestock manure, thus facilitating sustainable waste management [ 1 ]. The efficiency of AD is primarily dictated by such operational parameters as temperature, solid retention time (SRT), organic loading rate (OLR), and pH [ 2 ]. Temperature can play a critical role in determining the performance and stability of AD by shaping microbial ecosystems, regulating metabolic activity, affecting cell physiology, and mediating enzyme biosynthesis [ 3 , 4 ].…”

“…The physiological status of microbial cells can be damaged when exposed to inhibitors (e.g., capsaicin, microplastics, and antibiotics) and adverse metabolic conditions (e.g., temperature and pH changes) [ 2 , 14 ]. In these scenarios, cell membrane integrity and microbial viability would be reduced, intracellular substances would be released, and cell energy metabolism would be downregulated, resulting in poor biogas production [ 15 ].…”

“…Quite a few studies have examined the effects of temperature shift on AD microbial dynamics [ 2 , 19 ]. For instance, a decrease in temperature from 37 to 25 °C was found to increase the abundance of Proteobacteria in cattle manure digesters [ 20 ], while Ruminococcaceae and Methanobacterium were found to be the main drivers of digester resilience to abrupt temperature disturbances from 55 to 35 °C [ 19 ].…”

Understanding Anaerobic Co-digestion of Organic Wastes through Meta-Analysis

“…While a carbon-to-nitrogen (C/N) ratio of 20–30 is typically used to determine the co-substrate ratio (CR, %VS (on a volatile solid basis)), this alone may not ensure system stability. The ideal CR for maximizing methane production depends on the intrinsic qualities of the substrate, including its macromolecule and fiber composition, nutrient profile, and the presence or generation of potential inhibitors, such as long-chain fatty acids (LCFAs), sulfide, ammonia, humic acid, and dissolved lignin. − …”