Fate of Antibiotics and Antibiotic Resistance during Digestion and Composting: A Review

Abstract

Antibiotics and antibiotic-resistant bacteria (ARB) enter the environment through municipal and agricultural waste streams and pose a potential risk to human and livestock health through either direct exposure to antibiotic-resistant pathogens or selective pressure on the soil microbial community. This review summarizes current literature on the fate of antibiotics, ARB, and antibiotic resistance genes (ARGs) during anaerobic digestion and composting of manure and wastewater residuals. Studies have shown that removal of antibiotics varies widely during mesophilic anaerobic digestion, even within the same class of antibiotics. Research on ARB shows a wide range of removal under mesophilic conditions, with nearly complete removal under thermophilic conditions. Research on 16 antibiotics in 11 different studies using both bench-scale and farm-scale composting systems demonstrates that composting significantly reduces levels of extractable antibiotics in livestock manure in nearly all cases. Calculated half-lives ranged from 0.9 to 16 d for most antibiotics. There is more limited evidence that levels of ARB are also reduced by composting. Studies of the fate of ARGs show mixed evidence for removal during both mesophilic and thermophilic anaerobic digestion and during thermophilic composting. Antibiotic resistance genes are DNA structures, so they may persist until the DNA structure is degraded, yet the bacterium may have been rendered nonviable long before the DNA is completely degraded. Additional research would be of value to determine optimum anaerobic digestion and composting conditions for removal of ARB and to increase understanding of the fate of ARGs during anaerobic digestion and composting.

Antimicrobial Resistance in the Environment

“…Diverse removal patterns were observed for the antibiotics, ARBs and ARGs during anaerobic digestion which is in complete agreement with previously reported studies (Youngquist et al, 2016). ARGs was achieved by cyclic activated sludge system (Wen et al, 2016).…”

Sludge bio-drying: Effective to reduce both antibiotic resistance genes and mobile genetic elements

“…changes of bacterial community composition was influenced significantly by environmental factors like pH, the properties of available nutrition, temperature and MC, these factors may affect the ARGs profiles through bacterial community indirectly. The operational condition may be the primary factor that governs the evolution of bacterial community and the subsequent prevalence of ARGs as suggested previously in anaerobic digestion (Youngquist et al, 2016). Considering controlling the ARGs, more researches should be done to improve these environmental factors through optimization of the key operational parameters, just like what has been done in this study that the improved aeration strategy in Pile I realized the higher reduction and less enrichment of ARGs.…”

Effects of graphene oxide on the performance, microbial community dynamics and antibiotic resistance genes reduction during anaerobic digestion of swine manure

“…Considering the huge amounts of swine manure, anaerobic digestion (AD) was widely adopted due to its effectiveness on the pathogens removal, volume reduction and resource utilization, especially the biogas production, and luckily, it was demonstrated that AD could also realize some ARGs reduction in swine manure (Youngquist et al, 2016). But the digestate still contributed a lot to the spread and proliferation of ARGs in the environment (Sui et al, 2016) and there was much space for the improvement of AD efficiency (Astals et al, 2012), which indicated that some work could be done to simultaneously enhance the AD efficiency and ARGs removal.…”