Investigating the robustness of microbial communities in municipal sludge anaerobic digestion under organic loading rate disturbance

Anaerobic digestion (AD) frequently encounters disturbances due to variations in organic loading rates (OLRs), which can result in the failure of the sludge treatment process. However, there is a lack of comprehensive studies on the robustness of AD systems against OLR disturbances and the underlying mechanisms. In this study, the responses of reactor performance and active microbial communities in mesophilic AD were investigated and compared under conditions of OLR shock and OLR fluctuation. Statistical analysis confirmed that all reactors recovered from both types of OLR disturbance, indicating both functional and structural robustness of the mesophilic community. Based on metagenomics and metatranscriptomics analyses, it was observed that high diversity within the microbial community led to functional redundancy, which appears to be a key mechanism contributing to the robustness against OLR disturbances. Additionally, for the first time, the potential metabolic diversity of aerobic autotrophy bacteria in AD reactors was identified, including their roles in the utilization of glucose and acetate. Furthermore, the analysis of topological properties within the microbial interaction network was conducted, and the robustness of the community network was verified through the application of random node deletion attacks. The findings from this study provide valuable information for the effective regulation of microbial communities and the design of practical AD systems.