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Biomethane production via biogas upgrading is regarded as a future renewable gas, further boosting the biogas economy. Moreover, when upgrading is realized by the biogas CO2 conversion to CH4 using surplus renewable energy, the process of upgrading becomes a renewable energy storage method. This conversion can be carried out via microorganisms, and has attracted scientific attention, especially under thermophilic conditions. In this study, mesophilic conditions were imposed using a previously developed enriched culture. The enriched culture consisted of the hydrogenotrophic Methanobrevibacter (97% of the Archaea species and 60% of the overall population). Biogas upgrading took place in three lab-scale bioreactors: (a) a 1.2 L bubble reactor (BR), (b) a 2 L trickling bed reactor (TBR) filled with plastic supporting material (TBR-P), and (c) a 1.2 L TBR filled with sintered glass balls (TBR-S). The gas fed into the reactors was a mixture of synthetic biogas and hydrogen, with the H2 to biogas CO2 ratio being 3.7:1, lower than the stoichiometric ratio (4:1). Therefore, the feeding gas mixture did not make it possible for the CH4 content in the biomethane to be more than 97%. The results showed that the BR produced biomethane with a CH4 content of 91.15 ± 1.01% under a gas retention time (GRT) of 12.7 h, while the TBR-P operation resulted in a CH4 content of 90.92 ± 2.15% under a GRT of 6 h. The TBR-S operated at a lower GRT (4 h), yielding an effluent gas richer in CH4 (93.08 ± 0.39%). Lowering the GRT further deteriorated the efficiency but did not influence the metabolic pathway, since no trace of volatile fatty acids was detected. These findings are essential indicators of the process stability under mesophilic conditions. [ABSTRACT FROM AUTHOR]

Anaerobic digestion is a well-established technology for the sustainable production of biogas. However, to be used as a substitute for natural gas or as vehicle fuel, it is necessary to remove carbon dioxide (CO2) and other contaminants from biogas that can compromise the useful life of combustion engines. Upgraded biogas is known as biomethane (>95% methane content). This work reviews the different technologies used for upgrading biogas, emphasizing microalgae–nanoparticle systems, representing a more sustainable and environmentally friendly system. Parameters affecting these systems performance are discussed, and the trends and areas of opportunity for subsequent work are evaluated through a bibliometric analysis. [ABSTRACT FROM AUTHOR]

A high rate upflow anaerobic polyfoam‐based bioreactor (UAPB) was developed for lab‐scale in‐situ biogas upgrading by H2 injection. The reactor, with a volume of 440 mL, was fed with synthetic wastewater at an organic loading rate (OLR) of 3.5 g COD/L·day and a hydraulic retention time (HRT) of 7.33 h. The use of a porous diffuser, alongside high gas recirculation, led to a higher H2 liquid mass transfer, and subsequently to a better uptake for high CH4 content of 56% (starting from 26%). Our attempts to optimize both operational parameters (H2 flow rate and gas recirculation ratio, which is the total flow rate of recirculated gas over the total outlet of gas flow rate) were not initially successful, however, at a very high recirculation ratio (32) and flow rate (54 mL/h), a significant improvement of the hydrogen consumption was achieved. These operational conditions have in turn driven the methanogenic community toward the dominance of Methanosaetaceae, which out‐competed Methanosarcinaceae. Nevertheless, highly stable methane production rates of 1.4–1.9 L CH4/Lreactor.day were observed despite the methanogenic turnover. During the different applied operational conditions, the bacterial community was especially impacted, resulting in substantial shifts of taxonomic groups. Notably, Aeromonadaceae was the only bacterial group positively correlated with increasing hydrogen consumption rates. The capacity of Aeromonadaceae to extracellularly donate electrons suggests that direct interspecies electron transfer (DIET) enhanced biogas upgrading. Overall, the proposed innovative biological in‐situ biogas upgrading technology using the UAPB configuration shows promising results for stable, simple, and effective biological biogas upgrading. [ABSTRACT FROM AUTHOR]

The valorization of biogas as a renewable energy source faces a major obstacle regarding its purification. Siloxane is one of the impurities that cause problems such as damages to equipment of combustion engines, turbines, and boilers used for biogas conversion to heat and electricity. In this review, adsorption for siloxane removal is widely discussed, with two specific approaches: adsorbents sensitivity to water and regeneration, two essential points for industrial application. Thus, determining factors in adsorbents capacity, reusability, and water tolerance including textural properties, surface functional groups, and hydrophobicity are deeply analyzed. Studies oriented to the optimization of traditional adsorbents such as activated carbon, silica gel, and aluminosilicates as well as newly emerging adsorbents such as metal organic frameworks, graphene oxides, and waste-derived materials are studied in detail in terms of reusability and water tolerance. Although activated carbon is commercially used, its low selectivity, pore blockage due to siloxane polymerization, and unsuccessful regeneration make it disadvantageous. Silica gel, however, shows better reusability as a result of less adsorbent-adsorbate dissociation energy. In addition, aluminosilicates, despite its low adsorption capacity, proved to be more practical for real biogas due to their high hydrophobicity. Graphene oxide cost and energy efficiency in their synthesis make them more industrially appealing candidates despite their low adsorption capacity. Finally, metal organic frameworks demonstrated high selectivity, high adsorption capacity, and more efficient regeneration and therefore have more advantages and less drawbacks, although the number of published studies is still limited. [ABSTRACT FROM AUTHOR]

Biogas is a renewable source of energy that when upgraded can be adopted as a reliable and sustainable alternative. This study evaluates the performance of thermal swing adsorption technology applying resistive heating, in upgrading biogas obtained from anaerobic digestion to biomethane. Commercial coconut shell-based activated carbon was used as an adsorbent in the four-step cycle process to capture carbon dioxide, using a fabricated adsorption model. The influence of minor gas constituents of biogas in carbon dioxide breakthrough curves was analyzed. Dynamic adsorption tests were carried out to evaluate the system performance in carbon dioxide capture. The maximum regeneration temperature of 60 ℃ was found to have peak carbon dioxide concentration of 39% in the waste gas, maximum energy requirements of 0.1538 kWh per cycle, and an energy efficiency of 87%. This is a good trade-off between adsorbent recovery and system energy efficiency. The adoption of thermal swing adsorption technology in biogas upgrading systems is a viable alternative for water-deficient regions.

Energy policies around the world are increasingly highlighting the importance of hydrogen in the evolving energy landscape. In this regard, the use of hydrogen to produce biomethanol not only plays an essential role in the chemical industry but also holds great promise as an alternative fuel for global shipping. This study evaluates a system for generating biomethanol and biomethane based on anaerobic digestion, biogas upgrading, methanol synthesis unit, and high-temperature electrolysis. Thermal integration is implemented to enhance efficiency by linking the oxy-fuel gas turbine unit. The integrated system performance is evaluated through thermodynamic modeling, and Aspen Plus V12.1 is employed for the analysis. Our findings show that the primary power consumers are the Solid Oxide Electrolysis Cell (SOEC) and Methanol Synthesis Unit (MSU), with the SOEC system consuming 824 kW of power and the MSU consuming 129.5 kW of power, corresponding to a production scale of 23.2 kg/h of hydrogen and 269.54 kg/h of biomethanol, respectively. The overall energy efficiency is calculated at 58.09%, considering a production output of 188 kg/h of biomethane and 269 kg/h of biomethanol. The amount of carbon dioxide emitted per biofuel production is equal to 0.017, and the proposed system can be considered a low-carbon emission system. Key findings include significant enhancements in biomethanol capacity and energy efficiency with higher temperatures in the methanol reactor. [ABSTRACT FROM AUTHOR]

Anaerobic digestion under hydrogen (H2)/carbon dioxide (CO2)-versus nitrogen (N2)-purged conditions was examined for the potential for biogas enhancement in the presence of polylactic acid. With or without polylactic acid, H2/CO2 purging demonstrated a 25% higher methane (CH4) production, reaching approximately 160 NmL CH4/g VSadd compared to N2 purging. When H2/CO2 was purged with polylactic acid, there was reduced dominance of Spirochaetales, resulting in fewer intermediates that caused a similar amount of CH4 yield. Despite similar CH4 yield to conditions without polylactic acid, verification through Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) confirmed extensive polylactic acid decomposition. DSC revealed double melting peaks at 151.8 °C and 156.1 °C, indicating increased crystallinity and vigorous polylactic acid decomposition, particularly in the amorphous region, under H2/CO2 purging. This aligned with the decrease in the FTIR carbonyl index, visually confirmed using SEM. Metagenome sequencing highlighted the prevalence of hydrogenotrophic methanogens, Anaerolineales, Bacteroidales, and Thermoanaerobacterales under H2/CO2 purging, demonstrating higher polylactic acid degradation compared to N2 purging conditions. This study revealed a potential for biogas upgrading with waste management of polylactic acid. [ABSTRACT FROM AUTHOR]

The anaerobic digestion (AD) process is one of the most practiced technologies for the remediation of organic waste and maximization of energy recovery in terms of biogas or biomethane. The presence of other gaseous components in biogas, e.g. CO2 and H2S, often makes its direct application in engines and electricity production unsuitable. This work aimed to develop and utilize an algae-assisted microbial fuel cell (AMFC) for the purification of biogas by removing both CO2 and H2S and simultaneous bioelectricity generation. In addition to biogas clean-up, elemental sulfur recovery and CO2 utilization for algae cultivation add value to the proposed AMFC process. Experiments were performed with both sulfide and bicarbonate in their dissolved form, in the respective anodic and cathodic chambers of the AMFC. The sulfide concentration was varied from 100 to 800 mg/l and the AMFC exhibited a sulfide removal efficiency exceeding 97% at all concentrations tested. The process efficiency dropped, however, at sulfide concentrations above 300 mg/l in terms of both sulfide removal and power output. The AMFC performed best at 400 mg/l sulfide by exhibiting a power density of 24.99 mW/m3 and sulfide removal efficiency of 98.87%. The system exhibited columbic efficiency (CE %) in the range of 7.85–80%. The total alkalinity representing CO2, carbonate and bicarbonate levels in the algae-based system was reduced by 49.54%. The electrical energy recovered from the AMFC was 0.1 kWh/m3 and the total energy recovery, which is the sum of the electrical and algal lipid energy, amounted to 7.25 kWh/m3. [ABSTRACT FROM AUTHOR]

The availability of pollutants in biogas especially carbon dioxide hinders its application in the enginery parts by minimizing its calorific standards. The presence of CO2 contributes to global warming which is a worry globally. Thus, upgrading technologies is needed for safe utilization on small-scale and wide-range. The commercial technologies mostly discussed in the literature are pressure swing adsorption, membrane separation, physical scrubbing, and water scrubbing. These techniques are costly concerning investment, and operation costs, and are energy-intensive, especially on a small scale. Thus, difficult to apply especially in low-income economies, and necessitates the development of natural, low-cost sorbents for biogas upgrading like biomass, eggshell waste, and clay soil. The current review critically evaluates the potentiality of new approaches using low-cost sorbents for biogas upgrading. The review proposed that activating and additional of pore-forming materials in the adsorbents is necessary to significantly enhance their performance. [ABSTRACT FROM AUTHOR]

This study focused on enhancing the efficiency of methane upgrading and reducing energy consumption in the biogas upgrading process through the use of biphasic solvents. An aqueous-based biphasic solvent, comprising methyl monoethanolamine (MMEA), N-methyldiethanolamine (MDEA), and 1-butyl-3-methylimidazolium tetrafluoroborate (ItFB), was meticulously prepared. The biogas upgrading effect, regeneration efficiency, regeneration energy consumption, economic viability, selectivity, and phase separation characteristics of this absorbent were systematically analyzed. Various parameters, including different inlet flow rates, stirring rate, methane inlet concentrations, reaction temperatures, and amine mixing ratios, were adjusted to investigate their impact. A comprehensive evaluation was conducted on the biogas upgrading effect and substance migration trends of the biphasic solvent. Optimal process parameters were determined, demonstrating the favorable impact of the biphasic solvent on biogas upgrading. The upgraded gas achieved a methane purity exceeding 96%, and the regeneration energy consumption decreased by 44.27% compared to 30 wt.% MEA, resulting in a more than 50% improvement in economic efficiency. The interaction between the ionic liquid and carbamate facilitated the phase separation process, with carbon enrichment after separation exceeding 95%. This enhancement significantly contributed to the improvement of regeneration energy consumption. The study thus concludes that biphasic solvents, exemplified by the described aqueous-based solution, offer a promising avenue for effective biogas upgrading with notable advancements in economic and energy efficiency. [ABSTRACT FROM AUTHOR]

Scalable, low-cost biofuel and biochemical production can accelerate progress on the path to a more circular carbon economy and reduced dependence on crude oil. Rather than producing a single fuel product, lignocellulosic biorefineries have the potential to serve as hubs for the production of fuels, production of petrochemical replacements, and treatment of high-moisture organic waste. A detailed techno-economic analysis and life-cycle greenhouse gas assessment are developed to explore the cost and emission impacts of integrated corn stover-to-ethanol biorefineries that incorporate both codigestion of organic wastes and different strategies for utilizing biogas, including onsite energy generation, upgrading to bio-compressed natural gas (bioCNG), conversion to poly(3-hydroxybutyrate) (PHB) bioplastic, and conversion to single-cell protein (SCP). We find that codigesting manure or a combination of manure and food waste alongside process wastewater can reduce the biorefinery's total costs per metric ton of CO2 equivalent mitigated by half or more. Upgrading biogas to bioCNG is the most cost-effective climate mitigation strategy, while upgrading biogas to PHB or SCP is competitive with combusting biogas onsite.

Biogas upgrading via biomethanation has been extensively studied recently, but the influence of organic loading rate on process performance remains to be fully understood. This is particularly significant because both organic loading rate and hydrogen injection can lead to volatile fatty acid accumulation during anaerobic digestion. This study investigated the impact of a wide range of organic loading rates (from 1.25 to 3.25 g VS/L/d) on hydrogen consumption rates, organic acid accumulation, and microbial communities during in situ biomethanation. It also provided kinetics data and metabolite production data for different control reactors, including anaerobic digestion, ex situ biomethanation, and endogenous control reactors. Hydrogen was injected into parallel batch reactors using digestate from a semi-continuous lab-scale reactor subjected to increasing organic loading rates (1.25–3.25 g VS/L/d) as an inoculum. The inoculum was well adapted to each tested organic loading rate. The batch experiments were replicated following a 12 h hydrogen starvation period to assess the stability of hydrogen consumption rates. High organic loading rate values resulted in increased hydrogen consumption rates, peaking at 68 mg COD/L/h at an organic loading rate of 3.25 g VS/L/d (maximum value tested), with no significant organic acid accumulation despite the high hydrogen partial pressures. The hydrogen consumption rates were maintained after the starvation period. Furthermore, the addition of an organic substrate did not impact the hydrogen consumption rate (i.e., the in situ and ex situ rates were similar). A higher organic loading rate resulted in higher relative abundances of hydrogenotrophic methanogens (i.e., Methanospirillum sp.). This study highlights that increasing the organic loading rate can accelerate the rate of hydrogen consumption during in situ biomethanation, consequently reducing both capital and operational costs. [ABSTRACT FROM AUTHOR]

In this study, a field study was presented on upgrading the biogas generated from shrimp processing wastewater (sfw‐biogas) that had H2S of 5000–6000 ppm, CO2 13–32 %, and CH4 68–87 % using the oxidative absorption of H2S in iron‐chelated solution in series with vacuum pressure swing adsorption (VPSA). The regeneration of the adsorbent treating sfw‐biogas required a shorter evacuation time than that of treating the biogas with a typical composition of 60 % CH4 (t‐biogas). The VPSA process treating sfw‐biogas required half the evacuation time and 26 % lower energy consumption. However, the methane recovery decreased from 80 % for t‐biogas to 65 % for sfw‐biogas. [ABSTRACT FROM AUTHOR]

While energy-related sectors remain significant contributors to greenhouse gas (GHG) emissions, biogas production from waste through anaerobic digestion (AD) helps to increase renewable energy production. The biogas production players focus efforts on optimising the AD process to maximise the methane content in biogas, improving known technologies for biogas production and applying newly invented ones: H2 addition technology, high-pressure anaerobic digestion technology, bioelectrochemical technology, the addition of additives, and others. Though increased methane concentration in biogas gives benefits, biogas upgrading still needs to reach a much higher methane concentration to replace natural gas. There are many biogas upgrading technologies, but almost any has methane slip. This research conducted a life cycle assessment (LCA) on membrane-based biogas upgrading technology, evaluating biomethane production from biogas with variable methane concentrations. The results showed that the increase in methane concentration in the biogas slightly increases the specific electricity consumption for biogas treatment, but heightens methane slip with off-gas in the biogas upgrading unit. However, the LCA analysis showed a positive environmental impact for treating biogas with increasing methane concentrations. This way, the LCA analysis gave a broader comprehension of the environmental impact of biogas upgrading technology on GHG emissions and offered valuable insights into the environmental implications of biomethane production. [ABSTRACT FROM AUTHOR]

Anaerobic digestion is a well-established technology for the sustainable production of biogas. However, to be used as a substitute for natural gas or as vehicle fuel, it is necessary to remove carbon dioxide (CO2) and other contaminants from biogas that can compromise the useful life of combustion engines. Upgraded biogas is known as biomethane (>95% methane content). This work reviews the different technologies used for upgrading biogas, emphasizing microalgae–nanoparticle systems, representing a more sustainable and environmentally friendly system. Parameters affecting these systems performance are discussed, and the trends and areas of opportunity for subsequent work are evaluated through a bibliometric analysis.

Biomethane production via biogas upgrading is regarded as a future renewable gas, further boosting the biogas economy. Moreover, when upgrading is realized by the biogas CO2 conversion to CH4 using surplus renewable energy, the process of upgrading becomes a renewable energy storage method. This conversion can be carried out via microorganisms, and has attracted scientific attention, especially under thermophilic conditions. In this study, mesophilic conditions were imposed using a previously developed enriched culture. The enriched culture consisted of the hydrogenotrophic Methanobrevibacter (97% of the Archaea species and 60% of the overall population). Biogas upgrading took place in three lab-scale bioreactors: (a) a 1.2 L bubble reactor (BR), (b) a 2 L trickling bed reactor (TBR) filled with plastic supporting material (TBR-P), and (c) a 1.2 L TBR filled with sintered glass balls (TBR-S). The gas fed into the reactors was a mixture of synthetic biogas and hydrogen, with the H2 to biogas CO2 ratio being 3.7:1, lower than the stoichiometric ratio (4:1). Therefore, the feeding gas mixture did not make it possible for the CH4 content in the biomethane to be more than 97%. The results showed that the BR produced biomethane with a CH4 content of 91.15 ± 1.01% under a gas retention time (GRT) of 12.7 h, while the TBR-P operation resulted in a CH4 content of 90.92 ± 2.15% under a GRT of 6 h. The TBR-S operated at a lower GRT (4 h), yielding an effluent gas richer in CH4 (93.08 ± 0.39%). Lowering the GRT further deteriorated the efficiency but did not influence the metabolic pathway, since no trace of volatile fatty acids was detected. These findings are essential indicators of the process stability under mesophilic conditions.

Renewable energies present an opportunity to enhance energy security, reduce dependence on imports, and lower greenhouse gas emissions. Natural gas, viewed as a transitional fuel from coal to renewables, lacks reliable environmental sustainability and does not contribute to EU energy independence. Recently, biomethane has been gaining attention as an alternative to natural gas. Obtained from purified or "upgraded" biogas, it offers environmental and economic advantages. Several developed technologies, including absorption, adsorption, membrane separation, and cryogenic separation, are commercially available. However, those are energy- and resource-intensive. In this context, this review aims to examine the recent advancements in biogas upgrading, particularly in physical, chemical, and biological pathways. It focuses on CO2 removal and/or conversion to methane, offering an updated overview for future studies. The technologies are classified based on the separation method (by phase addition, by solid agent, by phase creation, and by biological process), and an analysis of each category is conducted. The discussion covers the economic and environmental characteristics, process complexity, and future research prospects in sustainable technologies. This review highlights the potential of biogas upgrading technologies in contributing to sustainable development, increasing energy security, and achieving greenhouse gas reduction goals that are aligned with EU targets. [ABSTRACT FROM AUTHOR]

• Starch- and petro-based bioplastics were anaerobically digested under H 2 /CO 2 or N 2. • Higher methane yield in H 2 /CO 2 than N 2 accomplishing successful biogas upgrading. • H 2 /CO 2 can enhance methane production with breakdown of starch-based bioplastic. To identify an economically viable waste management system for bioplastics, thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate) (PBAT) were anaerobically digested under hydrogen (H 2)/carbon dioxide (CO 2) and nitrogen (N 2) gas-purged conditions to compare methane (CH 4) production and biodegradation. Regardless of the type of bioplastics, CH 4 production was consistently higher with H 2 /CO 2 than with N 2. The highest amount of CH 4 was produced at 307.74 mL CH 4 /g volatile solids when TPS digested with H 2 /CO 2. A stepwise increased in CH 4 yield was observed, with a nominal initial increment followed by accelerated methanogenesis conversion as H 2 was depleted. This may be attributed to a substantial shift in the microbial structure from hydrogenotrophic methanogen (Methanobacteriales and Methanomicrobiales) to heterotrophs (Spirochaetia). In contrast, no significant change was observed with PBAT, regardless of the type of purged gas. TPS was broken down into numerous derivatives, including volatile fatty acids. TPS produced more byproducts with H 2 /CO 2 (i.e., 430) than with N 2 (i.e., 320). In contrast, differential scanning calorimetry analysis on PBAT revealed an increase in crystallinity from 10.20 % to 12.31 % and 11.36 % in the H 2 /CO 2 - and N 2 -purged conditions, respectively, after 65 days of testing. PBAT surface modifications were characterized via Fourier transform infrared spectroscopy and scanning electron microscopy. The results suggest that the addition of H 2 /CO 2 can enhance the CH 4 yield and increase the breakdown rate of TPS more than that of PBAT. This study provides novel insights into the CH 4 production potential of two bioplastics with different biodegradabilities in H 2 /CO 2 -mediated anaerobic digestion systems. [ABSTRACT FROM AUTHOR]

In addition to agriculture, Brazil stands out as one of the main meat exporters. In beef production, the waste from the slaughter of a 400-kg bovine produces about 26 kg of waste. In pig farming, the waste generated in the slaughter of a 90-kg pig corresponds to 2.7 kg. Both residues are potential substrates for the production of bioenergy through anaerobic digestion and co-digestion. Likewise, the biogas plants in operation in the country annually generate 1.83 BNm3 of biogas, and the sector is expanding since the national production capacity is 42.7 Bm3/year. This biogas generated through the biological process is an energy source that stands out due to the growing demand for technologies that offer clean energy. Renewable energy sources can ensure greater diversity in the world's energy matrix, in addition to reducing greenhouse gases emissions and dependence on fossil fuels. Therefore, this review addresses the fundamentals of anaerobic digestion and co-digestion, the environmental impacts of biogas and biomethane, and Brazil's energy potential for biogas production. In addition, we discussed the biogas purification technologies, the applications of biomethane, and the current scenario and perspectives of Brazilian biogas involving government initiative policies, technical regulation, international panorama, and economic, environmental, and legislative aspects. [ABSTRACT FROM AUTHOR]

Considering biogas upgrading to feed energy systems and its significant impact on the biogas energy density, a novel polygeneration system utilizing biogas from landfill waste is designed, simulated, and studied in this paper. The primary innovation is to design a biogas upgrading technology for a novel multigeneration system using a thermal matching approach. This system is capable of simultaneously generating power, providing heating, producing fresh water, and extracting liquid carbon dioxide in an environmentally sustainable manner, thus resulting in reduced environmental impacts. For this purpose, a cryogenic separation system based on liquefied natural gas cold utilization is employed for biogas upgrading and biomethane separation. The proposed process also consists of a Kalina cycle, an organic Rankine cycle, a multi-effect desalination technology, and a heating provider unit. This system is simulated within the Aspen HYSYS software and is undergone a comprehensive analysis from the viewpoints of energy, exergy, environmental, and economic. The results indicate that the proposed structure achieves energy and exergy efficiencies of 80.91% and 43.76%, respectively. Environmental assessment reveals that the emission intensity is 90.43% lower in polygeneration mode compared to power generation mode, and the system's net emission is equal to 23,041.51 kg/h. The economic evaluation demonstrates that the total unit cost of products is minimized in polygeneration operation (1.84 $/GJ), while it is highest in power generation condition (7.564 $/GJ). The investigations show that when a system is modified from a single generation to polygeneration, all thermodynamic, economic, and environmental indicators face an improvement. [Display omitted] • Design of a new trigeneration system using biogas upgrading and LNG regasification. • Sustainable scheme for producing power, heating, fresh water, and liquid carbon dioxide. • Aspen HYSYS is used for simulation and thermo-enviro-economic analysis is done. • Energy and exergy efficiencies of the whole system equal 80.91% and 43.76%. • Net emission and total unit cost of products equal 23,041.51 kg/h and 1.84 $/GJ. [ABSTRACT FROM AUTHOR]

Although biogas is a renewable energy source alternative to natural gas, it contains approximately 40 vol% CO2 and, hence, a low calorific value. The sequestration of CO2 from biogas is, therefore, essential before its widespread use. As CO2 can be easily solubilized as carbonate and bicarbonate in alkaline water, in this study, we isolated and characterized alkaliphilic wild microalgae that grow under high-level CO2 conditions and evaluated their application potential in CO2-removal from biogas. For this purpose, freshwater samples were enriched with 10 vol% CO2 and an alkaline culture medium (pH 9.0), wherein almost free CO2 was converted to carbonate and bicarbonate to yield alkaliphilic and high-level CO2-tolerant microalgae. Ten microalgal strains of Micractinium, Chlorella, Scenedesmus/Tetradesmus, or Desmodesmus spp. were isolated, some of which demonstrated good growth even under conditions of >pH 10 and >30 vol% CO2 . All algal strains grew well through fixing biogas-derived CO2 in a vial-scale biogas upgrading experiment, which reduced the CO2 level in biogas to an undetectable level. These strains yielded antioxidant carotenoids, including lutein, astaxanthin, zeaxanthin, and β-carotene, particularly rich in lutein (up to 7.3 mg/g dry cells). In addition, these strains contained essential amino acids, accounting for 42.9 mol% of the total amino acids on average, and they were rich in unsaturated fatty acids (comprising 62.2 wt% of total fatty acids). The present study identified strains that can contribute to biogas upgrading technology, and the present findings suggest that their biomass can serve as useful raw material across the food, nutraceutical, and feed industries. [ABSTRACT FROM AUTHOR]

This article reports the results of a discrete choice experiment with 183 German biogas plant operators designed to elicit the respondents' plans for biogas utilization pathways after the end of guaranteed feed‐in tariffs. Participants could choose between 'flexibilization' for demand‐based electricity generation and conversion to biomethane upgrading for direct feed‐in into the natural gas grid. A binomial logit model revealed a 37% probability of switching to biomethane upgrading. These plants are characterized by higher capacities, several involved shareholders, secured succession, costly digestate disposal and belonging to the upper performance quartile. Mixed logit estimations conducted separately for the two investment concepts revealed a very high overall willingness to invest: 71% for flexibilization and 82% for biomethane upgrading. The respondents demand a return on investment of 19% for flexibilization and 26% for biomethane upgrading. Within the flexibilization, twofold overbuilding (installed capacity equals 2 times the rated power) is clearly preferred to fivefold overbuilding. For the biomethane upgrading, private ownership of the upgrading plant is preferred to a joint investment in a central upgrading facility. Limiting the use of energy crops reduces the propensity to invest in both models, while a longer utilization period enhances it. The respondents consider lack of planning reliability as the biggest obstacle to invest, followed by long approval procedures and high investment costs due to restrictive legal requirements. [ABSTRACT FROM AUTHOR]

The removal of the main impurity CO2 is a crucial step in biogas upgrading. In this work, the separation of CO2 from CH4 on electrospun polyacrylonitrile-based carbon nanofibers (CNFs) is investigated using breakthrough experiments. The CNFs are prepared at various carbonization temperatures ranging from 600 to 900 °C and feature a tailorable pore size that decreases at higher carbonization temperatures. The adsorption properties of the different CNFs are studied measuring pure component isotherms as well as column breakthrough experiments. Adsorption kinetics are discussed using a linear driving force approach to model the breakthrough experiment and obtain the adsorption rate constant. Moreover, different approaches to determine the selectivity of the competitive CO2/CH4 adsorption are applied and discussed in detail. The results clearly prove that a size exclusion effect governs the adsorption selectivity on the CNFs. While CH4 cannot adsorb in the pores of CNFs prepared at 800 °C or above, the smaller CO2 is only excluded from the pores of CNFs prepared at 900 °C. For CNFs carbonized in the range from 600 to 750 °C, values of the CO2/CH4 selectivity of 11–14 are obtained. On the CNFs prepared at 800 °C the CH4 adsorption is severely hindered, leading to a reduced adsorbed amount of CH4 and consequently to an improved CO2/CH4 selectivity of 40. Furthermore, owing to the shrinking pores, the adsorption rates of CH4 and CO2 decrease with higher carbonization temperature. [ABSTRACT FROM AUTHOR]

Energy policies around the world are increasingly highlighting the importance of hydrogen in the evolving energy landscape. In this regard, the use of hydrogen to produce biomethanol not only plays an essential role in the chemical industry but also holds great promise as an alternative fuel for global shipping. This study evaluates a system for generating biomethanol and biomethane based on anaerobic digestion, biogas upgrading, methanol synthesis unit, and high-temperature electrolysis. Thermal integration is implemented to enhance efficiency by linking the oxy-fuel gas turbine unit. The integrated system performance is evaluated through thermodynamic modeling, and Aspen Plus V12.1 is employed for the analysis. Our findings show that the primary power consumers are the Solid Oxide Electrolysis Cell (SOEC) and Methanol Synthesis Unit (MSU), with the SOEC system consuming 824 kW of power and the MSU consuming 129.5 kW of power, corresponding to a production scale of 23.2 kg/h of hydrogen and 269.54 kg/h of biomethanol, respectively. The overall energy efficiency is calculated at 58.09%, considering a production output of 188 kg/h of biomethane and 269 kg/h of biomethanol. The amount of carbon dioxide emitted per biofuel production is equal to 0.017, and the proposed system can be considered a low-carbon emission system. Key findings include significant enhancements in biomethanol capacity and energy efficiency with higher temperatures in the methanol reactor.

Capturing CO2 is necessary to abate the climate crisis. Amine CO2 capture is the most mature technology but suffers from high thermal energy consumption for solvent regeneration. Heat pumps are a proven technology with which to electrify industrial processes. This study investigates an integrated heat pump system used to electrify an amine CO2 capture unit for a biogas upgrading process using aqueous monoethanolamine. The study evaluates the potential of such integrated systems through the overall energy consumption at varied stripper pressures between 0.313 to 1.813 bara and includes a techno-economic analysis to determine the levelized cost. The most optimal heat pump scenario utilizes a vacuum operated stripper at 0.513 bara and reduces the overall energy consumption by 68 % compared to a classical amine scrubbing unit. The techno-economic analysis shows that the levelized costs for biogas upgrading per MWh of produced biomethane may be reduced by up to 33 % from 47 €/MWh to 31 €/MWh by implementing heat pump electrification systems and a vacuum operated stripper compared to a scenario using natural gas.

An intelligent optimization of multistage gas permeation layouts is required to achieve high product gas purities and high product recoveries at the same time in gas separation technologies. In this work, a superstructure-based mathematical model for the optimization of CO 2 removal in three applications including post-combustion CO 2 capture, natural gas sweetening and biogas upgrading is designed. A typical polymeric membrane prepared within the BIOCOMEM project, with high CO 2 permeance, CO 2 /N 2 selectivity of 25, and CO 2 /CH 4 selectivity of 7.9 is studied to assess the potential of this membrane at a real industrial scale. Using a superstructure-based model, operating conditions, driving force distribution along each membrane stage, the use of feed compression and/or permeate vacuum, the number of stages and recycle options are simultaneously optimized. The techno-economic analysis of all three applications is then carried out and the most promising membrane-based process configuration was chosen. The multi-stage membrane process is investigated in terms of capture cost, energy consumption, and membrane area. The results revealed that high purity and recovery at a minimum cost could be achieved by the three-stage process in post-combustion CO 2 capture and natural gas while in biogas upgrading the two-stage configuration exhibited the best performance. It was found that a reduction in capture cost to around 42 €/tCO 2 is possible in post-combustion CO 2 capture if membranes with a selectivity of 50 and the same permeation flow are developed. [Display omitted] • A superstructure-based optimization approach for gas separation was designed. • Superstructure applied to CO 2 removal from flue gas, natural gas and biogas upgrading. • Techno-economic feasibility analysis on membrane system for CO 2 separation. • Approach was investigated in terms of cost, membrane area and power consumption. • The power consumption and capture cost are a strong function of CO 2 purity. [ABSTRACT FROM AUTHOR]

In this work, ASPENplus was used to simulate biogas upgrading by sorption-enhanced methanation in a dual interconnected bubbling fluidized bed configuration using inexpensive, abundant, and eco-friendly CaO to remove H2O from the reaction environment. The chemical looping scheme consisted of two reactors: a methanator/hydrator, where the catalytic reactions occurred on a catalyst with 20% Ni supported on alumina as well as the steam removal by CaO, and a regenerator, where the Ca(OH)2 was dehydrated back to CaO. The simulations were carried out to identify possible reactant compositions (H2 and biogas), CaO amount, and the methanation temperature able to produce an outlet gas matching the specifications for direct grid injection. When considering a stoichiometric gas feed ratio at the methanator inlet, the unwanted CaO carbonation worsened the process performance, subtracting CO2 from the desired methanation reaction. However, optimal conditions were found with hydrogen-lean gas feedings, balancing the limited H2 amount with the capture of CO2 due to the sorbent carbonation. Thermodynamic considerations pointed out the possibility of solid carbon formation induced by sorption-enhanced methanation conditions, especially for H2 sub-stoichiometric feedings. [ABSTRACT FROM AUTHOR]

Anaerobic membrane bioreactors (AnMBRs) are formed through the combination of anaerobic digestion and membrane technology. The upgraded technology separates SRT from HRT in the anaerobic digester, shortening the treatment period, reducing the digester's volume and improving effluent quality. Furthermore, AnMBRs have a strong tolerance for the existing forms of objects and can handle liquids, high-solid materials and gases. Up to now, AnMBRs have been utilized in the treatment of various types of industrial and municipal wastewater, organic solid waste and also biogas upgrading, and they have achieved excellent performance. However, there are few studies which have discussed their multiple utilization, especially following the flow of wastewater treatment. This study summarizes the application of AnMBRs in their diverse roles in the municipal wastewater treatment process. The discussion revolves around energy generation and the fouling issue of AnMBRs in the treatment of municipal wastewater, the digestion of sewage sludge generated in conventional municipal wastewater treatment and the upgrading of biogas after anaerobic digestion. In addition to controlling operating parameters, strategies used to improve the treatment effectiveness are also introduced. Lastly, online methods for preventing membrane fouling, which is the main operational obstacle to AnMBRs' wider spread, are also discussed. This review aims to provide a fresh perspective on how AnMBRs are utilized in waste treatment. [ABSTRACT FROM AUTHOR]

The current challenges of commercial cyclic adsorption processes for biogas upgrading are associated with either high energy consumption or low recovery. To address these challenges, this work evaluates the performance of a range of configurations for biogas separations, including pressure swing adsorption (PSA), pressure vacuum swing adsorption (PVSA), and twin double-bed PSA, by dynamic modelling. Moreover, a sensitivity analysis was performed to explore the effect of various operating conditions, including adsorption time, purge-to-feed ratio, biogas feed temperature, and vacuum level, on recovery and energy consumption. It was found that the required energy for a twin double-bed PSA to produce biomethane with 87% purity is 903 kJ/kg CH4 with 90% recovery, compared to 961 kJ/kg CH4 and 76% recovery for a PVSA process. With respect to minimum purity requirements, increasing product purity from 95.35 to 99.96% resulted in a 32% increase in energy demand and a 23% drop in recovery, illustrating the degree of loss in process efficiency and the costly trade-off to produce ultra-high-purity biomethane. It was concluded that in processes with moderate vacuum requirements (>0.5 bar), a PVSA should be utilised when a high purity biomethane product is desirable. On the other hand, to minimise CH4 loss and enhance recovery, a twin double-bed PSA should be employed. [ABSTRACT FROM AUTHOR]

Biogas upgrading is an important technique for biomethane production, a renewable source of energy with low carbon footprint. The presence of even small concentrations of impurities in biogas influences its properties at different levels. The effect of the individual component species on the biogas upgrading performance has not been fully evaluated and closely understood. In this work, biogas component species, including the typical binary biogas mixture (CH4/CO2) and one impurity with maximum concentration, flowing over silica gel bed are modelled and analyzed to study their effects on the biogas upgrading process. The model is built using Aspen Adsorption™ and Aspen Hysys version 10 and validated using experimental data reported previously. The effect of each component species is reported, and the deviation from the typical binary biogas mixture is marked. From our analyses, the presence of all the component species causes an adverse implication on the biogas upgrading performance. The presence of 20% nitrogen, for example, brings about the highest increase in viscosity and density of the biogas mixture, resulting in the highest friction factor between gas molecules and bed surface. Ten percent of moisture content causes the highest pressure drop during adsorption. Interestingly, 5% oxygen, 3% hydrogen, and 1% ammonia enhance the recovery of methane by 1.48%, 0.93%, and 0.56%, respectively. This study can be used to predict the biogas mixing behavior during the biomethane upgrading using pressure swing adsorption. The proposed model possesses a great competence for making prediction of biomethane upgrading performance of PSA process with impressive ability to disclose the influence of the common impurities on upgrading performance and biogas properties. [ABSTRACT FROM AUTHOR]

Biogas upgrading via biomethanation has been extensively studied recently, but the influence of organic loading rate on process performance remains to be fully understood. This is particularly significant because both organic loading rate and hydrogen injection can lead to volatile fatty acid accumulation during anaerobic digestion. This study investigated the impact of a wide range of organic loading rates (from 1.25 to 3.25 g VS/L/d) on hydrogen consumption rates, organic acid accumulation, and microbial communities during in situ biomethanation. It also provided kinetics data and metabolite production data for different control reactors, including anaerobic digestion, ex situ biomethanation, and endogenous control reactors. Hydrogen was injected into parallel batch reactors using digestate from a semi-continuous lab-scale reactor subjected to increasing organic loading rates (1.25–3.25 g VS/L/d) as an inoculum. The inoculum was well adapted to each tested organic loading rate. The batch experiments were replicated following a 12 h hydrogen starvation period to assess the stability of hydrogen consumption rates. High organic loading rate values resulted in increased hydrogen consumption rates, peaking at 68 mg COD/L/h at an organic loading rate of 3.25 g VS/L/d (maximum value tested), with no significant organic acid accumulation despite the high hydrogen partial pressures. The hydrogen consumption rates were maintained after the starvation period. Furthermore, the addition of an organic substrate did not impact the hydrogen consumption rate (i.e., the in situ and ex situ rates were similar). A higher organic loading rate resulted in higher relative abundances of hydrogenotrophic methanogens (i.e., Methanospirillum sp.). This study highlights that increasing the organic loading rate can accelerate the rate of hydrogen consumption during in situ biomethanation, consequently reducing both capital and operational costs.

The anaerobic conversion of surplus hydrogen to methane by hydrogenotrophic methanogen in an anaerobic digester has been attempted to overcome the drawbacks of hydrogen uselessly escaped from small or middle-scale industries. A biochemical methane potential test was thus performed to evaluate the methane production from hydrogen and carbon dioxide (H 2 /CO 2 = 4:1) injected directly into the reactors at mesophilic temperature (38 °C) for 30 days. The cumulative methane yield increased stepwise, ultimately reaching a maximum of 143.94 NmL CH 4 /g VS add at the end of the experiment, which was 56% higher than the control. After 7 days of incubation, the methane content in the biogas accounted for about 90%, whereas the control showed 10% lower than that. The kinetic study showed the injection of H 2 /CO 2 could reduce the rate of hydrolysis, verifying that the experimental data fit the first-order model better. In the meantime, microbial community analysis showed an increase in relative abundance of hydrogenotrophic methanogens, Methanobacteriales and Methanomicrobiales , in the sludge obtained after the test compared to before, indicating the increased methane yield was dominantly attributed to hydrogenotrophic methanogenesis. This study demonstrated that H 2 /CO 2 injection directly into the anaerobic digester was feasible for ultimately enhancing the quality of biogas. • Adding hydrogen and carbon dioxide increased methane up to 90%. • In this regard, hydrogenotrophic methanogen predominantly metabolized hydrogen. • Kinetics better fitted with the first-order model than modified Gompertz model. • This increased methane yield might derive to enhancingly apply for retrofitted AD. [ABSTRACT FROM AUTHOR]

Non-renewability and difficult access to fossil fuels can be replaced with renewable fuels, such as biogas. Due to the close structure of biogas to fossil fuels, it has become a powerful fuel for energy systems, especially when it enters the upgrading process. With this in mind, the proposed system proposes a novel trigeneration model integrated into a biogas upgrading unit, producing electricity, desalinated water, and methanol. This process is proposed for the first time, which is able to increase the thermodynamic, economic, and environmental performances compared to previous studies. Negative CO2 emission is its main feature that is available using a methanol synthesis unit. Thermal desalination and ammonia Rankine cycles are other equipment used in the proposed structure. The whole system is simulated in the Aspen HYSYS software and is investigated from the 4E aspect, namely energy, exergy, economics, and environment. Also, a sensitivity study is conducted. The overall energy and exergy efficiencies equal 51.54% and 87.39%, respectively. These criteria are improved between 4.54% and 15.64%-points and 32.29–74.70%-point compared to the existing literature review, respectively. In addition, the net CO 2 emission intensity equals −0.54 kg CO2 /kg MeOH , which is considerably lower than other relevant technologies (between 1.78 and 10.68 times). Moreover, the unit cost of methanol in the proposed process equals 0.21 $/kg, which is 63.54–85.61% lower than other methods available in the literature review. [Display omitted] • A new integrated trigeneration process based on biogas upgrading is presented. • 4E analysis of the process is done and results are compared with previous studies. • The biogas upgrading unit is responsible for the largest exergy destruction. • Overall energy and exergy efficiencies are 51.54% and 87.39%, respectively. • CO 2 emission and methanol cost equal − 0.54 kg CO 2 / kg MeOH and 0.21 $/kg, respectively. [ABSTRACT FROM AUTHOR]

Rising adverse impact of climate change caused by anthropogenic activities is calling for advanced methods to reduce carbon dioxide emissions. Here, we review adsorption technologies for carbon dioxide capture with focus on materials, techniques, and processes, additive manufacturing, direct air capture, machine learning, life cycle assessment, commercialization and scale-up. [ABSTRACT FROM AUTHOR]

With the current increase in demand for animal and agricultural products, management of agrowaste has become critical to avoid greenhouse gas emissions. The present article investigates the applicability of ammonium bicarbonate synthesis via flash distillation to valorize and stabilize several types of anaerobic digestates which are produced from individual fermentations of amino acids. The content of CO2 in the digestate was found to be responsible for the OH alkalinity (0.4 equivalents of acid/kg digestate), while the partial and total alkalinities (0.8 eq/kg digestate) were essentially derived from the content of NH3. The most suitable conditions for the flash distillation were 95 °C and 1 bar with the condensation occurring at 25 °C. However, in order to attain the precipitation of NH4HCO3 in the distillate, it was necessary to consider digestates with a moisture content of 50 wt.%, since saturation levels of inorganic nitrogen and inorganic carbon were not attained otherwise. Even under these conditions, few amino acids (i.e., arginine, glycine, and histidine) were able to provide an anaerobic digestate upon fermentation that would be suitable for NH4HCO3 stabilization. The process of stabilization with a capacity of a t of digestate per h was improved by adding hydrochloric acid or sodium hydroxide at a rate of 44 kg/h, leading to production of 34 kg NH4HCO3/h. Given the role of the volatile elements of the biogas as endogenous stripping agents, it is recommended to use a fresh and saturated digestate as feed for the flash distillation. [ABSTRACT FROM AUTHOR]

The catalytic performance in the direct CO 2 methanation of a model biogas is investigated on NiO–CeO 2 nanostructured mixed oxides synthesized by the soft-template procedure with different Ni/Ce molar ratios. The samples are thoroughly characterized by means of ICP-AES, XRD, TEM and HR-TEM, N 2 physisorption at −196 °C, and H 2 -TPR. They result to be constituted of CeO 2 rounded nanocrystals and of polycrystalline needle-like NiO particles. After a H 2 -treatment at 400 °C for 1 h, the surface basic properties and the metal surface area are also assessed using CO 2 adsorption microcalorimetry and H 2 -pulse chemisorption measurements, respectively. At increasing Ni content the Ni0 surface area increases, while the opposite occurs for the number of basic sites. Using a CO 2 /CH 4 /H 2 feed, at 11,000 cm3 h−1 g cat −1, CO 2 conversions in the 83–89 mol% range and methane selectivities >99.5 mol% are reached at 275 °C and atmospheric pressure, highlighting the very good performances of the investigated catalysts. • A series of NiO–CeO 2 mixed oxides is synthesized by the soft-template procedure. • All samples show high surface areas and strong interactions between NiO and CeO 2. • Small Ni0 crystallites (6–9 nm) are obtained upon reduction regardless of Ni content. • Good catalytic performance is obtained in the direct upgrading of a model biogas. • Depending on composition and temperature, different steps control the overall rate. [ABSTRACT FROM AUTHOR]

Biogas consists of mainly methane, as a source of energy, and impurities such as carbon dioxide, hydrogen sulphide, water, and siloxanes. These impurities, such as hydrogen sulphide, reduce the biogas energy content and corrode equipment that store, transport, or utilise biogas. Several reviews on upgrading biogas to biomethane have been published, but minimal focus has been put on upgrading biogas for commercialisation in South Africa. Thus, this study reviewed biogas upgrading techniques in South Africa to put together information on activities and experiences on biogas valorisation to enhance the chances for different stakeholders to learn and build on from local experiences. To capture all relevant information, literature from the past 10 years was retrieved from online databases and government, municipality, and companies' websites and institutional repositories. The review covered the sorption, separation, and in situ techniques that are globally used for upgrading biogas. The status of the biogas sector and the upgrading activities that occur in the country with their cost, energy, and environmental impacts were given in detail. It is estimated that a total of 3 million Nm3d−1 of biogas can be produced in the country from biogas substrates. Thus, researchers and entrepreneurs are encouraged to collaborate to utilise the abundant resources used for biogas production to enhance the commercialisation of biomethane. [ABSTRACT FROM AUTHOR]

Microbial electrolysis cells (MECs) permit to couple the oxidation of waste organic streams (e.g., wastewater, fermentate or digestate) with the reduction of carbon dioxide into products with a high market value (e.g., methane or acetic acid). MECs exploit the ability of electroactive microorganisms to use a solid electrode as final electron acceptor or donor. Here, a micro pilot tubular MEC has been set up combining the anodic oxidation of the organic matter with the bioelectromethanogenesis reaction in the cathodic chamber. Seven different synthetic feeding solutions, simulating a domestic wastewater or an acidogenic fermentate, have been used to test different C/N ratio on the performance of the MEC bioanode in the range between 25 and 0.4 (molC/molN). As a main result it was found that, under the same operating conditions (i.e., anode potential controlled at + 0.2 V vs SHE and HRT of 0.5 d), a high C/N ratio (e.g., 19 mol/mol) promotes the bioelectrochemical metabolism of the electroactive biofilm. These findings are relevant for a practical application of the technology considering the variable content of carbon and nitrogen in real feedstocks. [Display omitted] • The MEC allowed the production of 64 mL/L rea d of CH 4. • Raising the C/N ratio does increase the COD abatement. • A high nitrogen loading rate (2.2 gN/L rea d) decreased the energy consumption. • Electrochemical losses analysis showed the decrease of the system's overpotentials. • A high ammonium concentration (2 gN/L) inside the cathodic chamber inhibits the methanogenesis. [ABSTRACT FROM AUTHOR]

Biogas is a cornerstone within a clean and sustainable energy portfolio, while hydrogen production from biogas is a key enabler for methane conversion and carbon dioxide valorization for greenhouse gases emissions mitigation. In this work, pressure swing adsorption (PSA) configuration of two vessels-four adsorption beds connected in series was tested for upgrading low-grade biogas (50% CH 4 and 50% CO 2). To resolve CH 4 spillage issue, steam-methane reforming (SMR) plant was proposed as a green route for converting CH 4 and portion of CO 2 in the waste stream of PSA system into hydrogen. The integrated system (PSA-SMR) was performed on two stages i.e., PSA runs were conducted experimentally in lab while SMR system was simulated using Aspen Hysys software under operating conditions from a real plant. Response surface methodology was applied into Design Expert software to optimize the effects of system pressure, CH 4 concentration, and biogas/steam flowrate ratio on H 2 , CO 2 , H 2 O, and CO molar fractions in the product. The results revealed that four adsorption beds in serial configuration successfully recorded ultrapure CH 4 of 99.9% and recovery of 84.9% along with average CO 2 content of 60% in the waste stream. For SMR system, produced syngas comprised of 42.2% H 2 , 28.46% CO 2 , 13.84% N 2 , 8.88% H 2 O, and 6.66% CO with 100% conversion of the CH 4 and about 52.56% conversion of the CO 2. The optimum conditions that achieved the highest H 2 content of 51% from SMR were system pressure below 32 bar, methane content in feed stream ≥61%, and biogas/steam ratio in the range of 0.41–0.66 to record H 2. [Display omitted] [ABSTRACT FROM AUTHOR]

Energy may be generated in large quantities from fossil fuels, but this comes with environmental concerns. Thus, renewable resources like biogas, comprising carbon dioxide and methane, should be used alone or in combination with fossil fuels to mitigate the environmental footprints of energy generation systems. In this study, a new concept of hybrid solvent was presented, which combines 1-octyl-3-methylimidazolium tetrafluoroborate with aqueous mono diethanolamine for biogas upgrading process to provide high purity (≥ 99 wt%) and recovery (≥ 99 wt%) of biomethane. The process was simulated in ASPEN Plus® V.11. The thermodynamic framework was validated against experimental data, and rigorous regression was conducted to obtain binary parameters. To establish the efficacy of the suggested hybrid solvent, three scenarios were studied by altering the concentration of ionic liquid (5–20 wt%) linked with amine and compared to aqueous mono diethanolamine as the base case (50 wt%). The results showed that a hybrid solvent with 5 wt% 1-octyl-3-methylimidazolium tetrafluoroborate could increase CH4 purity to 99% (mol%). The hybrid solvent led to an energy saving of 64.94% compared to the amine-based system. Thermodynamic irreversibilities showed that 5 wt% 1-octyl-3-methylimidazolium tetrafluoroborate improved exergy efficiency by 54% over the amine-based procedure. Environmentally, the hybrid solvent system also achieved a higher capture rate (99%) and lower emissions (0.017 kW/kmol). Comparing the economic prospects, 5 wt% 1-octyl-3-methylimidazolium tetrafluoroborate saved 56% on total capital cost, making it competitive from an investment perspective.

Biomethanation is a prospective method to integrate a renewable solar or wind power grid with a biogas grid, where excess energy can be used to produce hydrogen for the biomethanation of the biogas to produce biomethane. The use of biotrickling filter reactors with appropriate carrier materials for biomethanation is essential for the immobilisation of hydrogenotrophic methanogens on the surface of the packing material. This study tested the suitability of filter materials made from woodchip ash (FA and CA) and glass waste (GF) for methanogenesis in biotrickling filter reactors using comparative performance analysis. The readily available and widely used expanded clay pallets (EC) and polyurethane foam (PUF) in biomethanation were used for comparison. The manometric method and BMP test are used to determine the rate of CH4 production. CH4 produced using filter materials decreases in the order GF>EC >PUF>FA>CA, respectively. The physical parameters of tested materials are compared to other filter materials commonly used in biomethanation applications. Glass foam (GF) that is made from glass waste showed the best biomethane production rate of 201.2 NmL/Lmaterial, as it has the best physical properties for methanogenesis in biotrickling filter reactors such as low volume density, high external porosity, and neutral pH. Ash waste recycling is related to its specific chemical properties, as it is alkaline and contains heavy metals that can leach out and negatively affect living organisms.

The selection of a local and sustainable use of biogas, and biogas feedstocks, towards the upgrading process to biomethane, is a key aspect towards more consistent energy planning within the frame of the EU Green Deal and Sustainable Development Goals. In this paper, four biomethane production and utilization pathways were assessed in the view of economic, environmental, technological, and social dimensions compared to a reference scenario in which direct biogas use in a cogeneration unit is assumed. The technologies analyzed included membrane systems, amine scrubbing, water scrubbing, and biological methanation, regarding the Sardinian context. The impact assessment was carried out using the TOPSIS method. As an output, thirteen consistent indicators reflecting the holistic aspect of sustainability were designed and proposed based on an in-depth literature review and the authors’ technological knowledge. The results show that the reference scenario was the preferable one. In terms of environmental and social considerations, biological methanation emerged as the most environmentally and socially responsible alternative. From the economic perspective, all the upgrading options depicted similar results. The technological-oriented weighting showed that the two most widespread upgrading options highlighted the optimal results.

Biomethanation is a prospective biogas upgrading method to integrate renewable energy grid with existing biogas grid. Biomethane can directly substitute fossil natural gas and be used in all energy sectors. The selection of packing material for the ex-situ biomethanation in biotrickling filter reactors can be based on the physical and chemical characterization of the carrier material. The packing material selected for biotrickling filter reactors supports hydrogenotrophic methanogenic growth and thereby increases the area for H2 mass transfer. Chemical components and melting temperature analysis of wood ash material are carried out to determine optimal parameters for producing wood ash filter material. Physical characteristics of new wood ash filter material such as volume-specific surface area (m2 m−3), the external porosity (vol. %) and bulk density (kg m−3) are carried out to compare this material with other carrier materials that have been used in biotrickling filter reactors before.