Densification pretreatment triggers efficient methanogenic performance and robust microbial community during anaerobic digestion of corn stover

Enhanced methane production through synergistic integration of quorum sensing Signals and microbial electrolysis in anaerobic digestion of low-quality biomass

This study explored the synergistic effects of exogenous acyl homoserine lactones (AHLs) and microbial electrolysis (ME) on enhancing anaerobic digestion (AD) of low-quality biomass. The combined AHLs + ME strategy achieved a 79.50 % increase in cumulative methane production compared to the control, outperforming individual treatments. This enhancement was attributed to accelerated substrate degradation, selective enrichment of hydrogenotrophic methanogens (Methanobrevibacter, Methanobacterium, Methanofollis), and strengthened quorum sensing, electron transfer, and methane synthesis pathways. Metagenomic analysis revealed abundance upregulation of key genes involved in AHL synthesis (bjaI, rpaI, braI, rhiI) and sensing (solR, cepR, tofR), direct interspecies electron transfer (pilA, mtrC), and hydrogenotrophic methanogenesis (ftr, mvhD, vhuD, vhcD). This study offers a novel and sustainable strategy to optimize methane production from recalcitrant biomass, advancing AD-based waste-to-energy systems.

Conductive materials enhance anaerobic membrane bioreactor (AnMBR) treating waste leachate at high organic loading rates

The treatment of landfill leachate using anaerobic membrane bioreactors (AnMBRs) often faces challenges such as poor removal efficiency, low methane yield and membrane fouling. This study applied AnMBRs with incrementally adding conductive materials to enhance the treatment of landfill leachate under high organic loading rates(35 kg COD/(m3∙d)). With 50 g/L activated carbon, COD removal percentages and methane yield increased to 81.03 ± 2.12% and 0.34 ± 0.01 m³ CH₄/kg COD, respectively. The addition of conductive materials dramatically increased EPS content of the sludge, which not only enhanced inter-microbial electron transmission but also increased the sludge's biological activity. The primary membrane fouling type for AnMBRs was cake layer, with Ca being the main inorganic foulant, and humic substances and proteins being the principal organic foulants. Combined cleaning methods effectively removed membrane foulants, resulting in total membrane flux recovery rates of higher than 96.5%. The conductive materials stimulated the enrichment and synergistic collaboration of acid-producing bacteria and methanogenic archaea.

The effects of different pretreatment technologies on microbial community in anaerobic digestion process: A systematic review

Here we comprehensively review the available knowledge on effects of different pretreatment technologies on microbial population and microbial dynamics in anaerobic digestion (AD) fed with different substrates and different operational parameters. To identify peer-reviewed studies published in English-language journals, a comprehensive search was performed across multiple electronic databases. The eligible studies were analyzed to extract data and information pertaining to the configuration of anaerobic reactors, operational parameters, and various pretreatment processes such as chemical, biological, enzymatic, thermal, microaerobic, and ultrasonic. The findings derived from this current review demonstrated that different chemical, biological, and physical pretreatment technologies improve the biomethane potential (BMP) and potentially affect the dominant bacteria and archaea. Moreover, although hydrogenotrophic methanogenesis are more observed due to resistance to extreme conditions, methane production follows both aceticlastic and hydrogenotrophic pathways in AD assisted with different pretreatment process. Firmicutes and Bacteroidetes phyla of bacteria were the dominant hydrolytic bacteria due to synergetic effects of different pretreatment process on solubilization and bioavailability of recalcitrant substrates. In summary, a holistic understanding on bacteria and archaea communities, along with the mechanisms of the dominant microorganisms leads to enhanced stability and overall performance of anaerobic digestion (AD) processes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40201-024-00917-x.

Metabolic responses and microbial community changes to long chain fatty acids: Ammonia synergetic co-inhibition effect during biomethanation

Anaerobic co-digestion is an established strategy for increasing methane production of substrates. However, substrates rich in proteins and lipids could cause a long chain fatty acids (LCFA)-ammonia synergetic co-inhibition effect. The microbial mechanisms of this co-inhibition are still unclear. The current study explored the effect of the synergetic co-inhibition on microbial community changes and prediction of metabolic enzymes to reveal the microbial mechanisms of the co-inhibition effect. The results indicated that during the synergetic co-inhibition, methanogens were mainly affected by ammonia. Decreased relative abundances of Petrimonas (82%) and Paraclostridium (67%) showed that ammonia inhibition contributed to the suppression of LCFA β-oxidation under the synergetic co-inhibition conditions. The accumulation of more LCFA could further suppress microorganisms' activities involved in several steps of anaerobic digestion. Finally, decrease of critical enzymes' abundances confirmed the synergetic co-inhibition effect. Overall, the current study provides novel insights for the alleviation of synergetic co-inhibition during anaerobic digestion.

Substance bioconversion, hydrolases activity, and metagenomic analysis to unravel the enhanced biomethanation of corn stover with urea-hydrothermal pretreatment

Corn stover (CS) is a promising feedstock for producing biomethane, that can replace diminishing fossil fuels. However, the recalcitrant structure of CS resulted in low degradability in anaerobic digestion (AD). Numerous studies investigated the pretreatment of CS before AD, but the insight mechanism of biomethanation enhancement is not fully revealed. Therefore, this study advanced low-temperature urea-hydrothermal pretreatment of CS, and the biomethane production, substance bioconversion, hydrolase activity, and metagenomic analysis were conducted to unravel the intrinsic mechanisms of pretreatment for the enhanced biomethanation. The results showed that the pretreatment improved 11.5% of the specific surface area of CS, providing 111.5% higher total volatile fatty acids and 19.9% higher reducing sugars than the control, potentially enriching more anaerobic microorganisms. As a result, the pretreated CS achieved 19.1% higher biomethane yield, 9.1% higher volatile solid removal rate, and 3 days shorter digestion time. The mass balance and microbial community succession analysis indicated that the pretreatment reinforced the biomethane conversion from carbohydrate, which was attributed to the rapid enrichment of hydrolytic acidification bacteria (g__unclassified_o__Bacteroidales) (33.2%) and mixotrophic archaea (Methanosarcina) (72.3%). Meanwhile, the activity of cellulase and xylanase was enhanced up to 23.7% and 66.7%. Metagenomic analysis revealed that the combined pretreatment of CS promoted methanogenesis by enhancing various CAZymes secretion (such as oligosaccharide-degrading enzymes), and functional genes expression of hydrolytic, acidification and acetate-methane pathways at days 1-5. The study indicated that the combined pretreatment could influence microbial composition and function by changing the physicochemical properties of the CS, thereby improving methanogenic performance.

Enhancement of anaerobic digestion of rice straw by amino acid-derived ionic liquid

This study proposes a novel method to enhance methane production from anaerobic digestion using an amino acid-derived ionic liquid, glycine hydrochloride, ([Gly][Cl]), as an exogenous additive. After 40 days of digestion with 5% [Gly][Cl], the cumulative methane production was 115.56 mL/g VS, which was 73% higher than that of the control group (without additive). Specifically, the peak activities of cellulase, xylanase, and lignin peroxidase were significantly higher than those of the control group. The addition of [Gly][Cl] increased bacterial diversity and reduced archaeal diversity. Synergistota represented by Syner-01, Fibrobacterota represented by BBMC-4, Bacteroides, and unclassified_f__Lachnospiraceae significantly increased in relative abundance. It suggested that [Gly][Cl] stimulated the activities of protein-hydrolyzing and acid-producing bacteria. [Gly][Cl] also increased the abundance of methanogens and archaea, converting more lignocellulose to methane. Methanobacterium, that metabolizes H₂ and CO₂ to CH₄, was more abundant. Therefore, [Gly][Cl] can improve methane yield as an anaerobic digestion additive.