Fate of antibiotic resistance genes and class 1 integrons during sludge treatment using pilot-scale anaerobic digestion with thermal hydrolysis pretreatment

Microbial degradation and pollutant control in aerobic composting and anaerobic digestion of organic wastes: A review

Aerobic composting (AC) and anaerobic digestion (AD) are promising technologies for organic waste treatment, but their efficiency and safety are influenced by complex waste composition and persistent contaminants. This review identifies the advances in understanding microbial community dynamics, enzymatic degradation pathways, and the fate of contaminants during AC and AD processes. The findings indicate that substrate composition shapes dominant microbial populations and their degradative enzymes, with this correlation potentially useful for predicting functional microbial communities. Additionally, AC shows advantages in antibiotic elimination while AD excels in heavy metal immobilization, with both contributing to removing certain antibiotic resistance genes (ARGs). The strategic manipulation of environmental conditions, particularly temperature and oxygen levels, can drive microbial succession to optimize organic matter decomposition while minimizing ARG proliferation. Economic analyses reveal that AC offers lower operational costs and AD generates valuable by-products with potential energy recovery from organic waste. Case studies indicate that integrating both technologies can overcome individual limitations and enhance degradation efficiency compared to conventional single-technology approaches. This work proposes a comprehensive framework for developing coupled AC-AD systems to achieve more efficient and safer organic waste valorization than conventional single-technology approaches. This review has important implications for advancing sustainable waste management practices and mitigating the spread of antibiotic resistance in the environment.

Antibiotic resistance genes in anaerobic digestion: Unresolved challenges and potential solutions

Antimicrobial resistance (AMR) threatens public health, necessitating urgent efforts to mitigate the global impact of antibiotic resistance genes (ARGs). Anaerobic digestion (AD), known for volatile solid reduction and energy generation, also presents a feasible approach for the removal of ARGs. This review encapsulates the existing understanding of ARGs and antibiotic-resistant bacteria (ARB) during the AD process, highlighting unresolved challenges pertaining to their detection and quantification. The questions raised and discussed include: Do current ARGs detection methods meet qualitative and quantitative requirements? How can we conduct risk assessments of ARGs? What happens to ARGs when they come into co-exposure with other emerging pollutants? How can the application of internal standards bolster the reliability of the AD resistome study? What are the potential future research directions that could enhance ARG elimination? Investigating these subjects will assist in shaping more efficient management strategies that employ AD for effective ARG control.

Fate of antibiotic resistance genes during sludge anaerobic fermentation: Roles of different sludge pretreatment

Excess sludge, the primary by-product of wastewater treatment plants, is the source and sink of antibiotic resistance genes (ARGs). Sludge pretreatments are an indispensable pathway to improve the resource recovery and harmfulness for anaerobic digestion sludge. However, fewer studies have compared the effects of different pretreatment technologies on the distribution of ARGs during anaerobic sludge digestion. Here, this study established seven anaerobic digesters, and four typical ARGs and one integrase gene of class 1 integron (intI1) regarded as the representative mobile genetic elements (MGEs) were examined during the whole anaerobic digestion process. It was found anaerobic digestion could effectively remove ARGs with about 70.86% removal rate of total ARGs. Among these pretreatments, the reduce efficiency of ARGs was the highest in 50 °C pretreatment, followed by oxidant, and the last was acid-alkaline. The microbial community analysis demonstrated the microbial community structure, including ARGs hosts and antibiotic resistant bacteria, was significantly changed and influenced by high temperature pretreatment. In addition, high temperature and K2S2O8 observably decrease the level of ROS production. Macro transcriptome analysis indicated that sludge pretreatment, except for 50 °C pretreatment, up-regulated the genes relevant to lyases and transferase, but down-regulated the genes responsible for peroxidase, antioxidant enzymes and T4SS gene. This study emphasized and compared the different sludge pretreatments on the fate of ARGs in anaerobic sludge, and highlighted concerns regarding the environmental and health risks to our society.

Leveraging machine learning for prediction of antibiotic resistance genes post thermal hydrolysis-anaerobic digestion in dairy waste

Anaerobic digestion holds promise as a method for removing antibiotic resistance genes (ARGs) from dairy waste. However, accurately predicting the efficiency of ARG removal remains a challenge. This study introduces a novel appproach utilizing machine learning to forecast changes in ARG abundances following thermal hydrolysis-anaerobic digestion (TH-AD) treatment. Through network analysis and redundancy analyses, key determinants of affect ARG fluctuations were identified, facilitating the development of machine learning models capable of accurately predicting ARG changes during TH-AD processes. The decision tree model demonstrated impressive predictive power, achieving an impessive R2 value of 87% against validation data. Feature analysis revealed that the genes intI2 and intI1 had a critical impact on the absolute abundance of ARGs. The predictive model developed in this study offers valuable insights for improving operational and managerial practices in dairy waste treatment facilities, with the ultimate goal of mitigating the spread of antibiotic resistance.

Effect of reactor operation modes on mitigating antibiotic resistance genes (ARGs) and methane production from hydrothermally-pretreated pig manure

Numerous efforts have been made to enhance the performance of anaerobic digestion (AD) for accelerating renewable energy generation, however, it remains unclear whether the intensified measures could enhance the proliferation and transmissions of antibiotic resistance genes (ARGs) in the system. This study assessed the impact of an innovative pig manure AD process, which includes hydrothermal pretreatment (HTP) and a two-stage configuration with separated acidogenic and methanogenic phases, on biomethane (CH4) production and ARGs dynamics. Results showed that HTP significantly increase CH4 production from 0.65 to 0.75 L/L/d in conventional single-stage AD to 0.82 and 0.91 L/L/d in two-stage AD. This improvement correlated with a rise in the relative abundance of Methanosarcina, a key methanogenesis microorganism. In the two-stage AD, the methanogenic stage offered an ideal environment for methanogens growth, resulting in substantially faster and higher CH4 production by about 10% compared to single-stage AD. Overall, the combined use of HTP and the two-stage AD configuration enhanced CH4 production by 40% compared to traditional single-stage AD. The abundance and diversity of ARGs were significantly reduced in the acidogenic reactors after HTP. However, the ARGs levels increased by about two times in the following methanogenesis stage and reached similar or higher levels than in single stage AD. The erm(F), erm(G), ant(6)-Ia, tet(W), mef(A) and erm(B) were the six main ARGs with significant differences in relative abundances in various treatments. The two-stage AD mode could better remove sul2, but it also had a rebound which elevated the risk of ARGs to the environment and human health. Network analysis identified pH and TVFAs as critical factors driving microbial communities and ARG proliferation in the new AD process. With the results, this study offers valuable insights into the trade-offs between AD performance enhancement and ARG-related risks, pinpointing essential areas for future research and practical improvements.

Performance of sewage sludge treatment for the removal of antibiotic resistance genes: Status and prospects

Wastewater treatment plants (WWTPs) receive wastewater containing antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARGs), which are predominant contributors to environmental pollution in water and soil. Of these sources, sludge is a more significant contributor than effluent. Knowing how sludge treatment affects the fate of ARGs is vital for managing the risk of these genes in both human and natural environments. This review therefore discusses the sources and transmission of ARGs in the environment and highlights the risks of ARGs in sludge. The effects of co-existing constituents (heavy metals, microplastics, etc.) on sludge and ARGs during treatment are collated to highlight the difficulty of treating sludge with complex constituents in ARGs. The effects of various sludge treatment methods on the abundances of ARGs in sludge and in soil from land application of treated sludge are discussed, pointing out that the choice of sludge treatment method should take into account various potential factors, such as soil and soil biology in subsequent land application. This review offers significant insights and explores the abundances of ARGs throughout the process of sludge treatment and disposal. Unintentional addition of antibiotic residues, heavy metals, microplastics and organic matter in sludge could significantly increase the abundance and reduce the removal efficiency of ARGs during treatment, which undoubtedly adds a barrier to the removal of ARGs from sludge treatment. The complexity of the sludge composition and the diversities of ARGs have led to the fact that no effective sludge treatment method has so far been able to completely eliminate the ecological risk of ARGs. In order to reduce risks resulting by transmission of ARGs, technical and management measures need to be implemented.