Biogas production is an established sustainable process for simultaneous generation of renewable energy and treatment of organic wastes. The increasing interest of utilizing biogas as substitute to ...natural gas or its exploitation as transport fuel opened new avenues in the development of biogas upgrading techniques. The present work is a critical review that summarizes state-of-the-art technologies for biogas upgrading and enhancement with particular attention to the emerging biological methanation processes. The review includes comprehensive description of the main principles of various biogas upgrading methodologies, scientific and technical outcomes related to their biomethanation efficiency, challenges that have to be addressed for further development and incentives and feasibility of the upgrading concepts.
•Data related to the development of commercial biogas upgrading plants are provided.•Physicochemical technologies for biogas upgrade are reviewed.•Biological biogas upgrading technologies are extensively presented.•Incentives and feasibility of biogas upgrading are discussed.•Biomethanation efficiencies from different upgrading technologies are compared.
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•Biogas upgrading to 82% CH4 is feasible in a thermophilic granular UASB reactor.•H2 is introduced in a separate chamber having a volume of 25% of the reactor.•H2 low gas-liquid mass ...transfer rate limits the availability of H2 for methanogens.•H2 distribution can be improved using porous inert devices, like ceramic sponge.•Gas recirculation and chamber configuration help to maximize CO2 conversion to CH4.
Biological biogas upgrading coupling CO2 with external H2 to form biomethane opens new avenues for sustainable biofuel production. For developing this technology, efficient H2 to liquid transfer is fundamental. This study proposes an innovative setup for in-situ biogas upgrading converting the CO2 in the biogas into CH4, via hydrogenotrophic methanogenesis. The setup consisted of a granular reactor connected to a separate chamber, where H2 was injected. Different packing materials (rashig rings and alumina ceramic sponge) were tested to increase gas-liquid mass transfer. This aspect was optimized by liquid and gas recirculation and chamber configuration. It was shown that by distributing H2 through a metallic diffuser followed by ceramic sponge in a separate chamber, having a volume of 25% of the reactor, and by applying a mild gas recirculation, CO2 content in the biogas dropped from 42 to 10% and the final biogas was upgraded from 58 to 82% CH4 content.
This study proposes an innovative setup composed by two stage reactors to achieve biogas upgrading coupling the CO2 in the biogas with external H2 and subsequent conversion into CH4 by ...hydrogenotrophic methanogenesis. In this configuration, the biogas produced in the first reactor was transferred to the second one, where H2 was injected. This configuration was tested at both mesophilic and thermophilic conditions. After H2 addition, the produced biogas was upgraded to average CH4 content of 89% in the mesophilic reactor and 85% in the thermophilic. At thermophilic conditions, a higher efficiency of CH4 production and CO2 conversion was recorded. The consequent increase of pH did not inhibit the process indicating adaptation of microorganisms to higher pH levels. The effects of H2 on the microbial community were studied using high-throughput Illumina random sequences and full-length 16S rRNA genes extracted from the total sequences. The relative abundance of archaeal community markedly increased upon H2 addition with Methanoculleus as dominant genus. The increase of hydrogenotrophic methanogens and syntrophic Desulfovibrio and the decrease of aceticlastic methanogens indicate a H2-mediated shift toward the hydrogenotrophic pathway enhancing biogas upgrading. Moreover, Thermoanaerobacteraceae were likely involved in syntrophic acetate oxidation with hydrogenotrophic methanogens in absence of aceticlastic methanogenesis.
Biogas and its opportunities-A review Kougias, Panagiotis G.; Angelidaki, Irini
Frontiers of environmental science & engineering,
06/2018, Letnik:
12, Številka:
3
Journal Article
Recenzirano
A comprehensive description of the biogas process is presented. Main operational parameters influencing the biogas process are reviewed. A historical overview of the biogas development is extensively ...presented. The current status of anaerobic digestion for biogas production is discussed. New horizons for exploitation and utilisation of biogas are proposed.
Biogas production is a well-established technology primarily for the generation of renewable energy and also for the valorization of organic residues. Biogas is the end product of a biological mediated process, the so called anaerobic digestion, in which different microorganisms, follow diverse metabolic pathways to decompose the organic matter. The process has been known since ancient times and was widely applied at domestic households providing heat and power for hundreds of years. Nowadays, the biogas sector is rapidly growing and novel achievements create the foundation for constituting biogas plants as advanced bioenergy factories. In this context, the biogas plants are the basis of a circular economy concept targeting nutrients recycling, reduction of greenhouse gas emissions and biorefinery purposes. This review summarizes the current state-of-the-art and presents future perspectives related to the anaerobic digestion process for biogas production. Moreover, a historical retrospective of biogas sector from the early years of its development till its recent advancements gives an outlook of the opportunities that are opening up for process optimisation.
The aim of this work was to elucidate the microbial ecology in twelve mesophilic and thermophilic full-scale biogas plants using a genome-centric metagenomic approach. In this study both biogas ...plants treating manure and those treating sludge from waste water treatment plants were considered. The identification of 132 Metagenome-Assembled Genomes (MAGs) and analysis of their abundance profile in different samples allowed the identification of the most abundant core members of the anaerobic digestion microbiome. Canonical correspondence analysis was used to determine the influence of biotic and environmental factors on MAGs abundance and to investigate the methanogenic performance of the biogas plants. Prediction of the functional properties of MAGs was obtained analyzing their KEGG pathways and their carbohydrate active domains. Network analysis allowed investigation of species-species associations and shed light on syntrophic interactions between members belonging to the anaerobic digestion dark matter (phylum Fermentibacteria). By stratifying and comparing different levels of information, it was predicted that some MAGs have a crucial role in the manure-supplemented thermophilic biogas plants and it was highlighted the importance of the glycine cleavage system in complementing the “truncated” Wood-Ljungdahl pathway.
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•Metagenomic binning identified core MAGs of the anaerobic digestion microbiome.•CCA revealed influence of biotic and environmental factors on MAGs abundance.•Functional properties of core MAGs were analyzed.•Network analysis revealed the syntrophic interactions between MAGs.
•Anaerobic digestion of diverse lignocellulosic substrates was examined.•The mechanical pretreatment methods enhanced the biodegradability of ensiled grass.•The most efficient mechanical method ...increased the methane yield of silage by 27%•Single and multiple linear regression were used to predict biomass digestibility.•The most efficient regressors were arabinan, lignin and protein contents.
Lignocellulosic substrates are associated with limited biodegradability due to the structural complexity. For that reason, a pretreatment step is mandatory for efficient biomass transformation which will lead to increased bioenergy output. The aim of the present study was to assess the efficiency of two pretreatment machines to enhance the methane yield of meadow grass. Specifically, the application of shearing forces with a rotated plastic sweeping brush against a steel roller significantly increased biomass biodegradability by 20% under relatively gentle operation conditions (600 rpm). The more intense operation (1200 rpm) was not associated with higher methane yield enhancement. Regarding an alternative machine, in which the brush was replaced with a coarse steel roller resulted in a more distinct effect (+27%) despite the lower rotating speed (∼400 rpm). Moreover, the association of the substrate’s individual chemical components and the practical methane yield was assessed, establishing single and multiple linear regression models. However, the estimation accuracy was rather low with either single (regressor: lignin, R2: 0.50) or multiple linear regression analyses (regressors: arabinan-lignin-protein, R2: 0.61). Results showed that poorly lignified plant tissue containing relatively high fractions of protein and arabinan is more susceptible to anaerobic digestion.
In typical anaerobic digestion (AD) systems, the microbial functional assertion is hampered by synchronised versatile metabolism required for heterogeneous substrates degradation. Thus, the intricate ...methanogenic process from organic compounds remains an enigma after decades of empirical operation. In this study, simplified AD microbial communities were obtained with substrate specifications and continuous reactor operation. Genome-centric metagenomic approach was followed to holistically investigate the metabolic pathways of the AD and the microbial synergistic networks. In total, 63 metagenome assembled genomes (MAGs) were assembled from 8 metagenomes acquired in specific methanogenic niches. The metabolic pathways were reconstructed from the annotated genes and their dynamicity under experimental conditions. The results show that the methanogenic niches nourish unique metabolism beyond current knowledge acquired from cultivation-based methods. A novel glucose mineralization model without acetate formation was proposed and asserted in a pair of syntrophs: Clostridiaceae sp. and Methanoculleus thermophilus. Moreover, the catabolic pathway was elucidated in uncharacterized syntrophic acetate oxidizers, Synergistaceae spp. A remarkable evolutionary insight is the discovery that electron transport and energy conservation mechanisms impose selective pressure on syntrophic partners. Overall, the functional roles of the individual microbes tightly rely on the catabolic pathways and cannot always be physiologically defined in accordance with conventional four-step AD concept. The substrate-specific systems provided a traceable microbial community to dissecting the AD process. The genome-centric metagenomics successfully constructed genomes of microbes that have not been previously isolated and illustrated metabolic pathways that beyond the current knowledge of AD process. This study provides new perspectives to unravel the AD microbial ecology and suggests more attention should be paid on uncharacterized metabolism specifically harboured by AD microbial communities.
•Genome-centric metagenomics was used to unveil the anaerobic digestion process.•Traceable microbial communities were obtained with substrate specifications.•The metabolisms were dissected by stepwise simplified substrates.•A novel glucose mineralization model without acetate formation was proposed.•Electron transfer mechanisms are key factors of selecting syntrophic partners.
•Biogas with more than 98% CH4 was produced in serial upflow and bubble column reactors.•Increased gas recirculation rate enhanced the biogas upgrading efficiency.•Biofilm was created on top of the ...diffuser surface in the bubble column reactor.•Abundance of novel phylotypes belonging to MBA08 and Bacteroidales sp.•Methanothermobacter thermautotrophicus was the most abundant methanogen.
Biogas upgrading is envisioned as a key process for clean energy production. The current study evaluates the efficiency of different reactor configurations for ex-situ biogas upgrading and enhancement, in which externally provided hydrogen and carbon dioxide were biologically converted to methane by the action of hydrogenotrophic methanogens. The methane content in the output gas of the most efficient configuration was >98%, allowing its exploitation as substitute to natural gas. Additionally, use of digestate from biogas plants as a cost efficient method to provide all the necessary nutrients for microbial growth was successful. High-throughput 16S rRNA sequencing revealed that the microbial community was resided by novel phylotypes belonging to the uncultured order MBA08 and to Bacteroidales. Moreover, only hydrogenotrophic methanogens were identified belonging to Methanothermobacter and Methanoculleus genera. Methanothermobacter thermautotrophicus was the predominant methanogen in the biofilm formed on top of the diffuser surface in the bubble column reactor.
This study evaluated the process performance and determined the microbial community structure of two lab-scale thermophilic trickling biofilter reactors used for biological methanation of hydrogen ...and carbon-dioxide for a total period of 94 days. Stable and robust operation was achieved by means of a single-pass gas flow. The quality of the output gas (>97%) was comparable to the methane purity achieved by commercial biogas upgrading systems fulfilling the specifications to be used as substitute to natural gas. The reactors' methane productivity reached >1.7 LCH4/(LR·d) at hydrogen loading rate of 7.2 LH2/(LR·d). The spatial distribution of the microbial consortia localized in the liquid media and biofilm enabled us to gain a deeper understanding on how the microbiome is structured inside the trickling biofilter. Sequencing results revealed a significant predominance of Methanothermobacter sp. in the biofilm. Unknown members of the class Clostridia were highly abundant in biofilm and liquid media, while acetate utilising bacteria predominated in liquid samples.
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•Biological biogas upgrading process was evaluated in trickling biofilter reactors.•Gas input was directed in concurrent or countercurrent flow of the trickling media.•Stable and robust operation was achieved by means of a single-pass gas flow.•Methane concentration in output gas was higher than 97%.•Hydrogenotrophic methanogens were localized in biofilm.
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•Ex situ biogas upgrading to 96% CH4 is achieved in thermophilic up-flow reactors.•The totality of H2 and CO2 is converted to CH4 reaching 0.25 LCH4/LH2 CH4 yield.•Higher gas ...recirculation and diffusers’ pore size improved gas-liquid contact.•H2 selectively enhances hydrogenotrophic methanogens and syntrophic bacteria.
This study evaluates the efficiency of four novel up-flow reactors for ex situ biogas upgrading converting externally provided CO2 and H2 to CH4, via hydrogenotrophic methanogenesis. The gases were injected through stainless steel diffusers combined with alumina ceramic sponge or through alumina ceramic membranes. Pore size, input gas loading and gas recirculation flow rate were modulated to optimize gas-liquid mass transfer, and thus methanation efficiency. Results showed that larger pore size diffusion devices achieved the best kinetics and output-gas quality converting all the injected H2 and CO2, up to 3.6L/LREACTOR·d H2 loading rate. Specifically, reactors’ CH4 content increased from 23 to 96% and the CH4 yield reached 0.25LCH4/LH2. High throughput 16S rRNA gene sequencing revealed predominance of bacteria belonging to Anaerobaculum genus and to uncultured order MBA08. Additionally, the massive increase of hydrogenotrophic methanogens, such as Methanothermobacter thermautotrophicus, and syntrophic bacteria demonstrates the selection-effect of H2 on community composition.
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