Inhibition of anaerobic digestion through accumulation of volatile fatty acids occasionally occurs as the result of unbalanced growth between acidogenic bacteria and methanogens. A fast recovery is a prerequisite for establishing an economical production of biogas. However, very little is known about the microorganisms facilitating this recovery. In this study, we investigated the organisms involved by a novel approach of mapping protein-stable isotope probing (protein-SIP) onto a binned metagenome. Under simulation of acetate accumulation conditions, formations of (13)C-labeled CO2 and CH4 were detected immediately following incubation with [U-(13)C]acetate, indicating high turnover rate of acetate. The identified (13)C-labeled peptides were mapped onto a binned metagenome for improved identification of the organisms involved. The results revealed that Methanosarcina and Methanoculleus were actively involved in acetate turnover, as were five subspecies of Clostridia. The acetate-consuming organisms affiliating with Clostridia all contained the FTFHS gene for formyltetrahydrofolate synthetase, a key enzyme for reductive acetogenesis, indicating that these organisms are possible syntrophic acetate-oxidizing (SAO) bacteria that can facilitate acetate consumption via SAO, coupled with hydrogenotrophic methanogenesis (SAO-HM). This study represents the first study applying protein-SIP for analysis of complex biogas samples, a promising method for identifying key microorganisms utilizing specific pathways.

Flexible biogas production that adapts biogas output to energy demand can be regulated by changing feeding regimes. In this study, the effect of changes in feeding intervals on process performance, microbial community structure, and the methanogenesis pathway was investigated. Three different feeding regimes (once daily, every second day, and every 2 h) at the same organic loading rate were studied in continuously stirred tank reactors treating distiller's dried grains with solubles. A larger amount of biogas was produced after feeding in the reactors fed less frequently (once per day and every second day), whereas the amount remained constant in the reactor fed more frequently (every 2 h), indicating the suitability of the former for the flexible production of biogas. Compared to the conventional more frequent feeding regimes, a methane yield that was up to 14% higher and an improved stability of the process against organic overloading were achieved by employing less frequent feeding regimes. The community structures of bacteria and methanogenic archaea were monitored by terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S rRNA and mcrA genes, respectively. The results showed that the composition of the bacterial community varied under the different feeding regimes, and the observed T-RFLP patterns were best explained by the differences in the total ammonia nitrogen concentrations, H 2 levels, and pH values. However, the methanogenic community remained stable under all feeding regimes, with the dominance of the Methanosarcina genus followed by that of the Methanobacterium genus. Stable isotope analysis showed that the average amount of methane produced during each feeding event by acetoclastic and hydrogenotrophic methanogenesis was not influenced by the three different feeding regimes.I nterest in a demand-driven biogas supply for flexible electricity production with the aim of balancing the supply of electricity generated from sources producing fluctuating amounts of electricity, such as solar and wind sources, has increased recently. Different strategies can be employed to obtain a demand-driven biogas supply, including a strategy involving a conventional biogas plant with biogas storage or a strategy involving a conventional biogas plant with a biogas upgrade to biomethane for subsequent storage in a natural gas grid (1-3). Conventional biogas production with integrated heat and power (CHP) plants are normally run on a semicontinuous substrate feeding regime in order to provide a constant biogas output and electricity generation (4).Alternatively, flexible biogas production that adapts biogas output to energy demand can be implemented by feeding management, including varying the feeding regimes and substrate composition. The production of larger amounts of biogas can be achieved immediately after feeding, and smaller amounts of biogas production are achieved during the nonfeeding period. Compared to the conventional operation of biogas plants with biogas storage, flexible biogas produc...

Background Commercial biogas upgrading facilities are expensive and consume energy. Biological biogas upgrading may serve as a low-cost approach because it can be easily integrated with existing facilities at biogas plants. The microbial communities found in anaerobic digesters typically contain hydrogenotrophic methanogens, which can use hydrogen (H 2 ) as a reducing agent for conversion of carbon dioxide (CO 2 ) into methane (CH 4 ). Thus, biological biogas upgrading through the exogenous addition of H 2 into biogas digesters for the conversion of CO 2 into CH 4 can increase CH 4 yield and lower CO 2 emission. Results The addition of 4 mol of H 2 per mol of CO 2 was optimal for batch biogas reactors and increased the CH 4 content of the biogas from 67 to 94%. The CO 2 content of the biogas was reduced from 33 to 3% and the average residual H 2 content was 3%. At molar H 2 :CO 2 ratios > 4:1, all CO 2 was converted into CH 4 , but the pH increased above 8 due to depletion of CO 2 , which negatively influenced the process stability. Additionally, high residual H 2 content in these reactors was unfavourable, causing volatile fatty acid accumulation and reduced CH 4 yields. The reactor microbial communities shifted in composition over time, which corresponded to changes in the reactor variables. Numerous taxa responded to the H 2 inputs, and in particular the hydrogenotrophic methanogen Methanobacterium increased in abundance with addition of H 2 . In addition, the apparent rapid response of hydrogenotrophic methanogens to intermittent H 2 feeding indicates the suitability of biological methanation for variable H 2 inputs, aligning well with fluctuations in renewable electricity production that may be used to produce H 2 . Conclusions Our research demonstrates that the H 2 :CO 2 ratio has a significant effect on reactor performance during in situ biological methanation. Consequently, the H 2 :CO 2 molar ratio should be kept at 4:1 to avoid process instability. A shift toward hydrogenotrophic methanogenesis was indicated by an increase in the abundance of the obligate hydrogenotrophic methanogen Methanobacterium . ...

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The off-line HPLC/DAD-NMR method is expedient for the unambiguous identication of structurally similar stilbenes in plant extracts.

BackgroundThe emerging cellulosic bioethanol industry will generate huge amounts of lignin-rich residues that may be converted into biogas by anaerobic digestion (AD) to increase the output of energy carriers from the biorefinery plants. The carbohydrates fraction of lignocellulosic biomass is degradable, whereas the lignin fraction is generally considered difficult to degrade during AD. The objective of this study was to investigate the feasibility of biogas production by AD from hydrolysis lignin (HL), prepared by steam explosion (SE) and enzymatic saccharification of birch. A novel nylon bag technique together with two-dimensional nuclear magnetic resonance spectroscopy, pyrolysis–gas chromatography–mass spectrometry (Py-GC/MS), and Fourier transform infrared (FTIR) spectroscopy was used to identify recalcitrant and degradable structures in the lignin during AD.ResultsThe HL had a lignin content of 80% which included pseudo-lignin and condensed-lignin structures resulting from the SE pretreatment. The obtained methane yield from HL was almost twofold higher than the theoretical methane from the carbohydrate fraction alone, indicating that part of the lignin was converted to methane. Characterization of the undegradable material after AD revealed a substantial loss of signals characteristic for carbohydrates and lignin–carbohydrate complexes (LCC), indicating conversion of these chemical components to methane during AD. The β-O-4′ linkage and resinol were not modified as such in AD, but major change was seen for the S/G ratio from 5.8 to 2.6, phenylcoumaran from 4.9 to 1.0%, and pseudo-lignin and condensed-lignin were clearly degraded. Scanning electron microscopy and simultaneous thermal analysis measurements demonstrated changes in morphology and thermal properties following SE pretreatment and AD. Our results showed that carbohydrate, LCC, pseudo-lignin, and condensed-lignin degradation had contributed to methane production. The energy yield for the combined ethanol production and biogas production was 8.1 MJ fuel per kg DM of substrate (4.9 MJ/kg from ethanol and 3.2 MJ/kg from methane).ConclusionThis study shows the benefit of using a novel bag technique together with advanced analytical techniques to investigate the degradation mechanisms of lignin during AD, and also points to a possible application of HL produced in cellulosic bioethanol plants.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1054-7) contains supplementary material, which is available to authorized users.

A unique method was developed and applied for monitoring methanogenesis pathways based on isotope labeled substrates combined with online membrane inlet quadrupole mass spectrometry (MIMS). In our study, a fermentation sample from a full-scale biogas plant fed with pig and cattle manure, maize silage, and deep litter was incubated with 100 mM of [2-(13)C] sodium acetate under thermophilic anaerobic conditions. MIMS was used to measure the isotopic distribution of dissolved CO2 and CH4 during the degradation of acetate, while excluding interference from water by applying a cold trap. After 6 days of incubation, the proportion of methane derived from reduction of CO2 had increased significantly and reached up to 87% of total methane, suggesting that synthrophic acetate oxidation coupled to hydrogenotrophic methanogenesis (SAO-HM) played an important role in the degradation of acetate. This study provided a new approach for online quantification of the relative contribution of methanogenesis pathways to methane production with a time resolution shorter than one minute. The observed contribution of SAO-HM to methane production under the tested conditions challenges the current widely accepted anaerobic digestion model (ADM1), which strongly emphasizes the importance of the acetoclastic methanogenesis.