Syngas biomethanation: effect of biomass-gas ratio, syngas composition and pH buffer

Microbiome re-assembly boosts anaerobic digestion under volatile fatty acid inhibition: focusing on reactive oxygen species metabolism

The accumulation of volatile fatty acids (VFAs) in anaerobic digestion (AD) systems resulting from food waste overload poses a risk of system collapse. However, limited understanding exists regarding the inhibitory mechanisms and effective strategies to address VFAs-induced stress. This study found that accumulated VFAs exert reactive oxygen species (ROS) stress on indigenous microbiota, particularly impacting methanogens due to their lower antioxidant capability compared to bacteria, which is supposed to be the primary reason for methanogenesis failure. To enhance the VFAs-stressed AD process, microbiome re-assembly using customized propionate-degrading consortia and bioaugmentation with concentrated digestate were implemented. Microbiome re-assembly demonstrated superior efficiency, yielding an average methane yield of 563.6±159.8 mL/L·d and reducing VFAs to undetectable levels for a minimum of 80 days. This strategy improved the abundance of Syntrophomonas, Syntrophobacter and Methanothrix, alleviating ROS stress. Conversely, microbial community in reactor with other strategy experienced an escalating intracellular damage, as indicated by the increase of ROS generation-related genes. This study fills knowledge gaps in stress-related metabolic mechanisms of anaerobic microbiomes exposed to VFAs and microbiome re-assembly to boost methanogenesis process.

Simultaneous adsorption and biodegradation of polychlorinated biphenyls using resuscitated strain Streptococcus sp. SPC0 immobilized in polyvinyl alcohol‑sodium alginate

Enhanced bioremediation of polychlorinated biphenyls (PCBs) is a promising and effective strategy for eliminating the risks posed by PCBs. In the present study, the feasibility of utilizing an immobilization approach to enhance the PCBs degradation performance of a resuscitated strain Streptococcus sp. SPC0 was evaluated. The results indicated that a mixed matrix containing polyvinyl alcohol (PVA) and sodium alginate (SA) used as immobilized carriers provided a porous microstructure space for SPC0 colonization and proliferation. The enhanced removal of PCBs by immobilized SPC0 was attributed to simultaneous adsorption and biodegradation performances of PVA-SA-SPC0 beads. The relative equilibrium adsorption capacity of immobilized beads increased with elevated initial concentration, and the maximum theoretical value calculated was 1.64 mg/g. The adsorption process of PCBs by immobilized beads was well fitted to the quasi-second-order kinetic model, and most suitable for Langmuir isotherm model. Immobilized SPC0 enhanced PCB removal with 1.0-7.1 times higher than free cells. Especially, more effective removal of PCBs at higher concentrations could be achieved, in which 73.9 % of 20 mg/L PCBs was removed at 12 h by immobilized SPC0, whereas only 12.0 % by free cells. Moreover, the immobilized SPC0 with excellent stability and reusability retained almost 100 % of the original PCBs removal activity after reusing four times. These results revealed the application potential of immobilizing resuscitated strains for enhanced bioremediation of PCBs.

Recent progress and challenges in biotechnological valorization of lignocellulosic materials: Towards sustainable biofuels and platform chemicals synthesis

Lignocellulosic materials (LCM) have garnered attention as feedstocks for second-generation biofuels and platform chemicals. With an estimated annual production of nearly 200 billion tons, LCM represent an abundant source of clean, renewable, and sustainable carbon that can be funneled to numerous biofuels and platform chemicals by sustainable microbial bioprocessing. However, the low bioavailability of LCM due to the recalcitrant nature of plant cell components, the complexity and compositional heterogeneity of LCM monomers, and the limited metabolic flexibility of wild-type product-forming microorganisms to simultaneously utilize various LCM monomers are major roadblocks. Several innovative strategies have been proposed recently to counter these issues and expedite the widespread commercialization of biorefineries using LCM as feedstocks. Herein, we critically summarize the recent advances in the biological valorization of LCM to value-added products. The review focuses on the progress achieved in the development of strategies that boost efficiency indicators such as yield and selectivity, minimize carbon losses via integrated biorefinery concepts, facilitate carbon co-metabolism and carbon-flux redirection towards targeted products using recently engineered microorganisms, and address specific product-related challenges, to provide perspectives on future research needs and developments. The strategies and views presented here could guide future studies in developing feasible and economically sustainable LCM-based biorefineries as a crucial node in achieving carbon neutrality.

Microbial community development during syngas methanation in a trickle bed reactor with various nutrient sources

Microbial community development within an anaerobic trickle bed reactor (TBR) during methanation of syngas (56% H₂, 30% CO, 14% CO₂) was investigated using three different nutrient media: defined nutrient medium (241 days), diluted digestate from a thermophilic co-digestion plant operating with food waste (200 days) and reject water from dewatered digested sewage sludge at a wastewater treatment plant (220 days). Different TBR operating periods showed slightly different performance that was not clearly linked to the nutrient medium, as all proved suitable for the methanation process. During operation, maximum syngas load was 5.33 L per L packed bed volume (pbv) & day and methane (CH₄) production was 1.26 L CH₄/L_pbv/d. Microbial community analysis with Illumina Miseq targeting 16S rDNA revealed high relative abundance (20-40%) of several potential syngas and acetate consumers within the genera Sporomusa, Spirochaetaceae, Rikenellaceae and Acetobacterium during the process. These were the dominant taxa except in a period with high flow rate of digestate from the food waste plant. The dominant methanogen in all periods was a member of the genus Methanobacterium, while Methanosarcina was also observed in the carrier community. As in reactor effluent, the dominant bacterial genus in the carrier was Sporomusa. These results show that syngas methanation in TBR can proceed well with different nutrient sources, including undefined medium of different origins. Moreover, the dominant syngas community remained the same over time even when non-sterilised digestates were used as nutrient medium. KEY POINTS: • Independent of nutrient source, syngas methanation above 1 L/L_pbv/D was achieved. • Methanobacterium and Sporomusa were dominant genera throughout the process. • Acetate conversion proceeded via both methanogenesis and syntrophic acetate oxidation.