Recognition of core microbial communities contributing to complex organic components degradation during dry anaerobic digestion of chicken manure

Overcoming Extreme Ammonia Inhibition on Methanogenesis by Artificially Constructing a Synergistically Community with Acidogenic Bacteria and Hydrogenotrophic Archaea

High total ammonia nitrogen (TAN) inhibits anaerobic digestion (AD) and cannot be completely eliminated by merely enhancing a stage of AD. This study incorporates TAN-tolerant inoculum into substrates hydrolyzed by Rhizopus mixed agents to simultaneously enhance hydrolysis-acidogenesis-methanogenesis. The results show a 16.46-fold increase in CH4 production under TAN-inhibited (6870.97 mg L-1) conditions, even exceeding the AD without TAN by 21.10%. Model substrates sodium acetate and mixed H2 confirm hydrogenotrophic methanogenesis is the main pathway, with reduced TAN inhibition. Furthermore, a synergistic metabolic microbial community dominated by hydrolytic bacteria JAAYGG01 sp. and DTU014 sp., acidogenic bacteria DTU015 sp., DTU013 sp., and JAAYLO01 sp., and methanogens Methanosarcina mazei and an unclassified species in the Methanoculleus is reconstructed to resist TAN inhibition. Metagenomic combined with metatranscriptomic sequencing identifies that this microbial community carries xynD and bglB to regulate substrate hydrolysis, leading to acetate production through glycolysis, butyrate, and pyruvate metabolism with high acetate kinase activity, thereby CH4 produced primarily via hydrogenotrophic methanogenesis with high coenzyme F420 activity, facilitated by efficient mass transfer processes and quorum sensing regulation. This cleaner strategy obtains higher economic benefit (US$149.02) than conventional AD and can increase 154.64-fold energy production of a 24 000 m3 biogas plant, guided by machine learning.

Insights into links between redox cycling of dissolved organic matter ranked by molecular weight and methanogen-bacteria symbiosis-driven methane production

Molecular weight (MW) of dissolved organic matter (DOM) governs its redox capacity, playing pivotal roles in methanogen-bacteria symbiosis-driven CH4 production. However, the effect of redox capacity of DOM ranked by MW on these symbiotic associations during anaerobic digestion have never been investigated. The electron-donating (EDC) and -accepting capacity (EAC) of DOM with different MW were quantified, elucidating their impacts on bacteria-methanogen symbiosis-driven CH4 production. By contrast, DOM with 7000 > MW > 14,000 Da constituted the primary contribution to EAC, with an average contribution of 44.63 %. DOM with MW > 14,000 Da emerged as the predominant contributor to EDC, with an average contribution of 49.10 %. Random forest showed that EAC/EDC of DOM ranked by MW was the important factors for methanogenesis by driving shifts in microbial symbiotic relationships. 46 genera (relative abundance of 69.55 %) of microorganisms exhibited robust associations with EAC/EDC. EDC of DOM with 3500 < MW < 7000 Da exerted positive effect on CH4 by modulating the corporation of Caldicoprobacter, norank_o__TSCOR001-H18, norank_o__MBA03 and Methanobrevibacter. EDC of DOM (7000 < MW < 14,000 Da) promotes CH4 production by regulating cooperation of Corynebacterium, Pseudomonas and Methanosarcina, Methanothermus. EDC of DOM (MW > 14,000 Da) enhances CH4 production by modulating cooperation of Ureibacillus, Treponema and methanomassiliicoccus, methanogenium. EAC of DOMs were negatively correlated with CH4. This study broadens our knowledge on the intricate process of methanogenesis and holds significant importance in developing a microbial symbiosis regulation strategy based on electron transfer system.

Insight into response mechanism of short-chain fatty acids to refined microbial transformation order of dissolved organic matter ranked by molecular weight during dry anaerobic digestion

Dynamic transformation of dissolved organic matter (DOM) contributes to short-chain fatty acids (SCFAs) production during anaerobic digestion. However, the impact of refined transformation of DOM ranked by molecular weight (MW) on SCFAs has never been investigated. Results indicated that DOM conversion order was 3500-7000 Da>(MW>14000 Da) > 7000-4000 Da during hydrolysis stage, while it was independent of their MW in acidogenesis phase and followed a low to high MW order during methanogenesis stage. Proteins-like DOMs with different MW were closely related to SCFAs. Eight groups of microorganisms (e.g., Bacillus and Caldicoprobacter) responsible for the conversion of proteins-like DOMs to SCFAs. The possible routes linking environmental properties to microorganisms-proteins-like DOMs-SCFAs connections were constructed. Microbial activity modifications by regulating moisture, pH, NO3--N and NH4+-N can expedite the conversion of proteins-like DOMs to SCFAs. The study emphasizes the importance of MW-classification-based biotransformation of organic waste, offering a potential strategy to enhance anaerobic digestion performance.

Response of fulvic acid linking to redox characteristics on methane and short-chain fatty acids in anaerobic digestion of chicken manure

Fulvic acids (FAs) is formed during the bioconversion of organic matter (OM) to biogas during anaerobic digestion (AD) and has a complex structure and redox function. However, the evolutionary mechanisms of FAs during AD and its interactions with acid and methane production have not been sufficiently investigated, especially at different stages of AD. Intermittent AD experiments by chicken manure and rice husk showed significant structural changes and reduced aromatization of FAs (e.g., O-H stretch6, 14.10-0%; SR, 0.22-0.60). The electron donating capacity (EDC) [9.76-45.39 μmole-/(g C)] and electron accepting capacity (EAC) [2.55-5.20 μmole-/(g C)] of FAs showed a tendency of decreasing and then increasing, and FAs had a stronger electron transfer capacity (ETC) in the methanogenic stage. Correlation analysis showed that the EDC of FAs was influenced by their own structure (C-O stretch2, C-H bend1, C-H bend4, and N-H bend) and also had an inhibitory effect on propionic production, which further inhibited acetic production. The EAC of FAs was affected by molecular weight and had a promoting effect on methane production. Structural equation modelling identified three possible pathways for AD. The C-O stretch2 structure of FAs alone inhibits the production of propionic. In addition, pH can directly affect the EDC of FAs. This study provides a theoretical basis for the structural and functional evolution of FAs in AD of chicken manure on the mechanism of methane production.

Effect of biochar derived from biogas residue on methane production during dry anaerobic fermentation of kitchen waste

Kitchen wastes (KW) dramatically increasing with population and economy enhancing, and dry anaerobic fermentation was used to treat it. However, the large amount of biogas residue severely restricted the application of dry anaerobic fermentation, because the high total solid might lead to the system failure. Therefore, it is urgent to find appropriate way to improve the efficiency of dry anaerobic fermentation and reduce the great amount of biogas residue. In this study, a tentative experiment was conducted to investigate the effect of biochar prepared from biogas residue on the performance of dry anaerobic fermentation system. The results showed that almost half of the biogas residue was reduced and converted into biochar. At the presence of biochar, methane yield was 308.6 mL/gVS, which was 10.5% higher than that of control. Compared to the system without biochar, the highest volatile fatty acid (VFA) concentration was 19.3% higher and the percentage of acetate and valerate was 25.3％ and 12.8％, while it was 16.3% and 22.0% in the control, suggesting that biochar accelerated the degradation of VFA. Bacteria community diversity increased, Fastidiosipila and Proteiniphilum enriched at the presence of biochar, which might accelerate the hydrolysis and acidification of KW. Hydrogenotrophic methanogens was dominated and syntrophic acetate oxidation was the primary pathway to produce methane. This study developed a new recycle route for improving the efficiency of dry anaerobic fermentation while reducing the large amount of biogas residue generated from dry anaerobic fermentation.

Synergistic ammonia and fatty acids inhibition of microbial communities during slaughterhouse waste digestion for biogas production

The slaughterhouse waste (SHW) contains high organics which makes SHW a feasible feedstock for anaerobic digestion (AD). The present study systematically assessed the microbiome response and biomethanation along with the production of volatile fatty acids (VFAs) and ammonia under 2%, 4%, 6%, and 8% (w v^-1) loadings of SHW in AD. The optimum loading was 2% SHW which resulted in maximum biomethane production and VFAs consumption. A higher SHW concentration (4% and 6%) resulted in a prolonged lag-phase and decreased biomethane production. High VFAs (28.88 g L^-1) and ammonia nitrogen (>4 g L^-1) accumulation were observed at 8% SHW leading to permanent inhibition of biomethane and methanogenic archaea. An increase in ammonia and VFAs concentration, at 4% and 6% SHW loadings, shifted the methanogenic pathway from acetoclastic to hydrogenotrophic lead by Methanoculleus. Acetoclastic Methanosaeta (77.15%) dominated the reactors loaded with 2% SHW resulting in the highest biomethane production.

The synergistic effect of rumen cellulolytic bacteria and activated carbon on thermophilic digestion of cornstalk

To explore the bioaugmentation of rumen cellulolytic bacteria (RCB) and activated carbon (AC) on thermophilic digestion of cornstalk, biochemical methane potential tests were carried out. Adding RCB or AC can improve methane production, while simultaneous existence of AC (10 g/L) and RCB (5%) obtained the best performance. The maximum cellulose degradation rate, methane production rate and methane yield were 66.92%, 32.2 L/(kgVS·d), and 144.9 L/kgVS, which increased by 30.23%, 51.17%, and 20.35% compared with control group. The cellulolytic and fermentative bacteria (Hydrogenispora), syntrophic acetate-oxidizing bacteria (norank_o_MBA03), and hydrogenotrophic Methanothermobacter were crucial for thermophilic digestion of cornstalk. The enhancement of AC was due to the enrichment of Hydrogenispora and Methanothermobacter, while RCB can increase the abundance of cellulolytic bacteria (Halocella and norank_o_M55-D21) and mixotrophic Methanosarcina. The synergetic effect of AC and RCB owing to the enriched cellulolytic bacteria, the enhanced syntrophic acetate oxidation and the concentrated carbon metabolic flow to methane.

Effect of liquid volume and microflora source on degradation rate and microbial community in corn stover degradation

Degradation is the bottleneck in the utilization of crop straw. In this paper, we screened the microbial consortia degrading corn stover from straw degrading consortia MC1 (M), sheep feces (Y), and mixtures (Q) of M, Y, and cattle feces. The effects of microflora source and liquid volume (representing dissolved oxygen) on the microbial community and degradation rate of corn stover were investigated. The results showed that the degradation rate and cellulase activity of a 200 mL liquid volume (L2) were significantly higher than that of 100 mL (L1). Microflora source had a significant effect on bacterial and fungal diversity, composition and taxa. Q and Y had higher bacterial and fungal α-diversity than that of M. The degradation rate was significantly correlated with cellulase activity but not with microbial diversity. This indicated that liquid volume had a significant effect on degradation rate while microflora source had a significant effect on microbial community in corn stover degradation.