The responses of mesophilic and thermophilic anaerobic digestion of municipal sludge to periodic fluctuation disturbance of organic loading rate

Anaerobic digestion of microalgae: microbial response and recovery after organic loading disturbances

Industrial anaerobic digestion (AD) represents a relevant energy source beyond today's fossil fuels, wherein organic matter is recycled to methane gas via an intricate and complex microbial food web. Despite its potential, anaerobic reactors often undergo process instability over time, which is frequently caused by substrate composition perturbations, making the system unreliable for stable energy production. To ensure the reliability of AD technologies, it is crucial to identify microbial and system responses to better understand the effect of such perturbations and ultimately detect signatures indicative of process failure. Here, we investigate the effect of the microalgal organic loading rate (OLR) on the fermentation product profile, microbiome dynamics, and disruption/recovery of major microbial metabolisms. Reactors subjected to low- and high-OLR disturbances were operated and monitored for fermentation products and biogas production over time, while microbial responses were investigated via 16S rRNA gene amplicon data, shotgun metagenomics, and metagenome-centric metaproteomics. Both low- and high-ORL fed systems encountered a sudden decline in methane production during OLR disturbances, followed by a recovery of the methanogenic activity within the microbiome. In the high-OLR disturbances, system failure triggered an upregulation of hydrolytic enzymes, an accumulation of fermentation products, and a shift in the methanogenic population from hydrogenotrophic to acetoclastic methanogens, with the latter being essential for recovery of the system after collapse.

IMPORTANCE

Anaerobic digestion (AD) with microalgae holds great potential for sustainable energy production, but process instability caused by substrate disturbances remains a significant barrier. This study highlights the importance of understanding the microbial dynamics and system responses during organic loading rate perturbations. By identifying key shifts in microbial populations and enzyme activity, particularly the transition from hydrogenotrophic to acetoclastic methanogens during recovery, this research provides critical insights for improving AD system stability and can contribute to optimizing microalgae-based AD processes for more reliable and efficient methane production.

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.

Effects of sudden shock load on simultaneous biohythane production in two-stage anerobic digestion of high-strength organic wastewater

The two-stage anaerobic digestion (AD) for biohythane production is a sustainable solution, but it is sensitive to organic shock load that disrupts reactors and inhibits biohythane production. This study investigated biohythane production, reactor performance, and the possibility of post-failure restoration in a two-stage AD system designed for treating high-strength organic wastewater. Sudden shock load was applied by increasing the OLR threefold higher after reaching steady state phase. During shock load phase, hydrogen content, hydrogen yield and methane production rate (MPR) reached its peak values of 62.61 %, 1.641 mol H2/mol glucose, and 1.003 L CH4/L⋅d respectively before declining significantly. Interestingly, during the restorative phase, hydrogen production sharply declined to nearly zero, while methane production exhibited a resilience and reached its peak methane content of 52.2 %. The study successfully demonstrated the system's resilience to sudden shock load, ensuring stable methane production, while hydrogen production did not exhibit the same capability.

High-rate anaerobic digestion of sewage sludge using anaerobic dynamic membrane bioreactor under various sludge composition and organic loading rates

This study investigates the effects of sludge compositions and organic loading rates (OLRs) on stable biomethane production during sludge digestion. Batch digestion experiments evaluate the effects of alkaline-thermal pretreatment and waste activated sludge (WAS) fractions on the biochemical methane potential (BMP) of sludge. A lab-scale anaerobic dynamic membrane bioreactor (AnDMBR) is fed with a mixture of primary sludge and pretreated WAS. Monitoring of volatile fatty acid to total alkalinity (FOS/TAC) helps maintain operational stability. The highest average biomethane production rate of 0.7 L/L·d is achieved when the OLR, hydraulic retention time, WAS volume fraction, and FOS/TAC ratio are 5.0 g COD/L·d, 12 days, 0.75, and 0.32, respectively. This study finds functional redundancy in two pathways: hydrogenotrophic and acetolactic. An increase in OLR promotes bacterial and archaeal abundance and specific methanogenic activity. These results can be applied to the design and operation of sludge digestion for stable, high-rate biomethane recovery.