Abstract：
Organic loading rate (OLR) is crucial for determining the stability of dry anaerobic digestion (AD). Digestate recirculation contributes to reactor stability and enhances methane production. Nevertheless, the understanding of how OLR and digestate recirculation affect the abundance and diversity of antibiotics and antibiotic resistance genes (ARGs), as well as the mechanisms involved in the dissemination of ARGs, remains limited. This study thoroughly investigated this critical issue through a long-term pilot-scale experiment. The metabolome analyses revealed the enrichment of various antibiotics, such as aminoglycoside, tetracycline, and macrolide, under low OLR conditions (OLR ≤ 4.0 g·VS/L·d) and the reactor instability. Antibiotics abundance decreased by approximately 19.66-31.69 % during high OLR operation (OLR ≥ 6.0 g·VS/L·d) with digestate recirculation. The metagenome analyses demonstrated that although low OLR promoted reactor stability, it facilitated the proliferation of antibiotic-resistant bacteria, such as Pseudomonas, and triggered functional profiles related to ATP generation, oxidative stress response, EPS secretion, and cell membrane permeability, thereby facilitating horizontal gene transfer (HGT) of ARGs. However, under stable operation at an OLR of 6.0 g·VS/L·d, there was a decrease in ARGs abundance but a notable increase in human pathogenic bacteria (HPB) and mobile genetic elements (MGEs). Subsequently, during reactor instability, the abundance of ARGs and HPB increased. Notably, during digestate recirculation at OLR levels of 6.0 and 7.0 g·VS/L·d, the process attenuated the risk of ARGs spread by reducing the diversity of ARGs hosts, minimizing interactions among ARGs hosts, ARGs, and MGEs, and weakening functional profiles associated with HGT of ARGs. Overall, digestate recirculation aids in reducing the abundance of antibiotics and ARGs under high OLR conditions. These findings provide advanced insights into how OLR and digestate recirculation affect the occurrence patterns of antibiotics and ARGs in dry AD.
摘要：
有机负荷率（OLR）对于确定干式厌氧消化（AD）的稳定性至关重要。消化再循环有助于反应器稳定性并提高甲烷产量。然而，对OLR和消化物再循环如何影响抗生素和抗生素抗性基因（ARGs）的丰度和多样性的理解，以及传播ARGs的机制，仍然有限。这项研究通过长期的中试实验彻底调查了这一关键问题。代谢组分析揭示了各种抗生素的富集，如氨基糖苷，四环素,和大环内酯,在低OLR条件下(OLR≤4.0g·VS/L·d)和反应堆不稳定性。在消化物再循环的高OLR操作（OLR≥6.0g·VS/L·d）期间，抗生素丰度降低了约19.66-31.69％。宏基因组分析表明，尽管低OLR促进了反应器的稳定性，它促进了抗生素抗性细菌的增殖，如假单胞菌，以及与ATP生成相关的触发功能概况，氧化应激反应，EPS分泌，和细胞膜通透性，从而促进ARGs的水平基因转移(HGT)。然而,在OLR为6.0g·VS/L·d的稳定运行下，ARGs丰度下降，但人类致病菌（HPB）和可移动遗传元件（MGEs）显着增加。随后，在反应堆不稳定期间，ARGs和HPB的丰度增加。值得注意的是,在OLR水平为6.0和7.0g·VS/L·d的消化物再循环期间，该过程通过降低ARGs宿主的多样性来降低ARGs传播的风险，最大限度地减少ARGs主机之间的交互，ARGs,和MGE,和削弱与ARGsHGT相关的功能概况。总的来说,消化物再循环有助于在高OLR条件下减少抗生素和ARGs的丰度。这些发现为OLR和消化物再循环如何影响干AD中抗生素和ARGs的发生模式提供了深入的见解。
