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Food waste is a significant issue in many developed and emerging countries and has significant environmental, social, and economic impacts. As China's urban population increases and restaurants expand, so does food wastage, resulting in many environmental and social issues. Therefore, this study investigates how the economic feasibility and environmental benefits of energy generation using biogas from food waste in Jiangsu Province can help achieve sustainable development goals and China's 14th Five-Year Plan. This study used Buswell's formulation, mathematical formulation, and economic metrics methods to analyze data from 2004 to 2020. The findings of the study are as follows: 1. The results show that 109.1 Mt. of food waste was produced in Jiangsu Province. 2. The total amount of electricity production potential from biogas yield during the 17 years is 16,126.0 GWh. 3. The study revealed that 3090.32 million tons (3.43% of the coal employed for energy production during the period) of coal combustion could be saved. 4. This prevented the release of 7262.26 million kilograms of carbon dioxide, 149.49 million kilograms of nitrous oxide, and 996.63 million kilograms of methane emissions. 5. The avoided coal consumption also helped reduce global warming by 76,727.33 kt of CO 2 equivalent. 6. The project is economically beneficial with a shorter net present value (NPV) for 1 year, a positive NPV (US$34.7 Million), an internal rate of return (23%), a return on investment (33.0%), and a lower levelized cost of energy (US$ 0.039/kWh). Policy recommendations are also discussed. • Electricity production potential from food waste in Jiangsu is analyzed. • The economic feasibility and environmental impacts were assessed. • Biogas derived from food waste has a high electricity generation potential. • Food waste to energy project is economically viable. • Food waste-to-energy projects can save coal combustion. [ABSTRACT FROM AUTHOR]

Biogas has gained increasing consideration as a competitive, environmentally benign, and sustainable alternative to fossil fuels. These benefits of biogas necessitate the need for intercontinental transportation, which is challenging because of its low energy density. Liquefaction is a viable approach to increase energy density, but this approach is energy and cost-intensive and requires high purity of biomethane. Cryogenic biogas upgrading integrated with the biomethane liquefaction (or bio-LNG) process is an efficient technique to meet these challenges due to its dual benefits: separation with high purity/recovery and precooling of biomethane. This study evaluates different cryogenic technologies (distillation, controlled freeze zone (CFZ), and anti-sublimation) and their integration potential with the bio-LNG production process from a technical and economic perspective. This type of comparative assessment is not found in the open literature. In addition, the CFZ process has not been investigated previously for biogas upgrading. The processes are designed and simulated in Aspen Hysys v14. Among all these processes, the CFZ performs better due to its single-column operation, which reduces cost and energy requirements. The results reveal that the CFZ process is an efficient and economical integrated process, boasting high exergy efficiency (40%), competitive energy consumption (0.30 kWh/kg), and a low production cost (6.3 $/MMBtu). This study can help process engineers design an improved biogas supply chain in terms of cost and energy. • Controlled freeze zone process is introduced for biogas upgrading. • Comparative assessment of cryogenic technologies is conducted. • CFZ process is energy-efficient and low-cost (OPEX) process. • Energy, exergy, and economic analyses are performed. [ABSTRACT FROM AUTHOR]

The production of biogas for energy generation through the anaerobic digestion is seen as an effective way to exploit local renewable resources as a substitute of fossil fuels. The two main applications that are currently adopted are the electricity production through biogas internal combustion engines, potentially combined with heat recovery, and the biogas upgrading to biomethane, to be supplied to the natural gas infrastructure. This research work contributes to the discussion by analyzing the performance of a real biogas plant in Italy, based on the anaerobic digestion of the organic fraction of municipal solid waste, that has shifted from power generation to biomethane generation. The performance of the two configurations is compared by means of the expected CO 2 emissions savings against the current average electricity in Italy and natural gas carbon intensities, including upstream emissions. The results show that, based on the assumptions of our analysis for the current context of Italy, 1 MWh of biogas from organic fraction of municipal solid waste can lead to 152 kg CO2,eq savings if upgraded to biomethane and injected into the grid, but only to 120 kg CO2,eq when used in engines running in full-electric mode. If the engines are also producing useful heat, emission savings increase, reaching a trade-off with biomethane if 31% of the annual heat production can be recovered. However, considering the expected 2030 electricity mix in Italy, biomethane production would still be the best solution to maximize emission savings. Performance data from real plants are an important resource to develop reliable and effective energy system models, that can support policy makers in defining local energy plans and decarbonization strategies. • We compare combined heat and power from biogas vs upgrading to biomethane. • Our results are based on the monthly operation of a real plant over multiple years. • The results show the importance of heat recovery to support emission savings. • The national electricity mix is a key parameter to be considered in the comparison. • The best energy use of biogas in terms of CO2 emissions depend on multiple aspects. [ABSTRACT FROM AUTHOR]

Production of electrolytic hydrogen and its conversion to methane, also known as power-to-gas (PtG), could play a key role in the transition towards a defossilised energy system. Integration of PtG technology with wastewater treatment and co-digestion presents an opportunity to produce low-carbon methane while simultaneously upgrading biogas, recycling biogenic carbon dioxide and utilising process by-products (heat and oxygen). A model of such an integrated system was developed using real plant data to assess the techno-economic performance through simulation of hourly operation and configuration optimisation. The integrated concept was demonstrated to be a promising option for increasing efficiency and reducing costs and emissions in the PtG system. By-product utilisation increased net energy efficiency from 52.3 to 59.7 % HHV , leading to a reduction in levelised cost of PtG (LCOPtG) of 1.0 % and in net specific emissions of 28.3 % and 2.2 % based on average and marginal grid emission factors respectively. Minimum LCOPtG of 194.6 €/MWh CH4 was achieved, which entailed average and marginal net specific emissions of 37.2 and 635.2 gCO 2 /kWh CH4 , respectively. In the investigated conditions, the optimised PtG configuration produced heat in excess, but could not fulfil oxygen demand at the wastewater treatment plant. Heat integration yielded considerable performance improvements, while oxygen integration provided only minor benefits and slightly increased overall production costs. However, improved economic performance of oxygen integration was shown to be possible depending on local conditions. Although integrating several independent systems introduced the challenge of managing fluctuating heat and oxygen demand, alongside the varying supply of biogas and renewable electricity, the difference in magnitude between by-product generation and demand meant that their utilisation had only a minor impact on system operation. [Display omitted] • An hourly-based model of a locally integrated PtG system was developed. • Configuration optimisation led to minimum production cost of 194.6 €/MWh. • Heat and oxygen use altered production costs by −2 % and + 1 %, respectively. • The system produced heat in excess, but could not meet oxygen demand. • Biogas upgrading via PtG increased costs by 54 % compared with amine scrubbing. [ABSTRACT FROM AUTHOR]

As Europe faces the dual challenge of decarbonizing its energy sector while ensuring energy security, REPowerEU reinforces the ambitious targets outlined in the Green Deal, complementing the "Fit for 55" package. This work analyses sustainable biomethane production in Europe, with a specific focus on Italy, and its conversion into sustainable fuels. Under the light of existing policy targets and regulatory instruments, the study explores innovative and sustainable agro-energy chains, with biomethane as energy vector for producing sustainable aviation fuels (SAF) and methanol for maritime. Decentralized biomass digestion and centralized biomethane conversion in refinery are combined, considering three key Gas-to-Liquid (GTL) pathways: Fischer-Tropsch and methanol synthesis, and gas fermentation/alcohol-to-jet. A simulation model was used to estimate the performances of these routes, providing insights on process yields and energy balances. Additionally, preliminary investment cost estimates are considered by reviewing existing references and extrapolating unit-specific cost data. As by 2030 biomethane in Europe could supply 38 bcm, the routes analysed could cover 4 to 11% of jet fuel demand, and from 25 to 56% of maritime fuel needs. By 2050, with a potential EU biomethane supply of 91 bcm, these pathways might meet 9–25% of jet fuel demand, and 48–105% of maritime fuel demand. In Italy, by 2030, 5.6 bcm of biomethane could enable these pathways to meet 7–18% of jet fuel demand, and a remarkable 69–152% of maritime fuel demand. By 2050, with 8.2 bcm of biomethane, these routes might cover 8–22% of jet fuel demand, and potentially satisfy 91–198% of maritime fuel demand. Moreover, these pathways would also yield other added-value by-products (e.g. naphtha, diesel, waxes, hydrogen, gasoline), which should be considered in comparing them. The average investment costs for each route were estimated at 791,970 USD/t/day for the Fischer-Tropsch based GTL plant, 130,275 USD/t/day for the methanol-based GTL plant, and 669,740 USD/t/day for the GTL plant involving gas fermentation/alcohol-to-jet conversion. [Display omitted] • Decentralized biomethane-centralized Gas-to-Liquid can decarbonize EU aviation and maritime sectors. • By 2030, GTL routes may satisfy 4–11% jet fuel and 25–56% of maritime fuel EU demands. • By 2050, 9–25% of jet and 48–105% of maritime fuel EU needs could be covered by these paths. • 2030 Italian jet fuel (7–18%) and maritime (69–152%) demands could be met by these routes. • At 2050, 8–22% of jet fuel and 91–198% of maritime needs could be satisfied for Italy. [ABSTRACT FROM AUTHOR]

This paper aims at evaluating the best allocation of potential biomethane generation for the decarbonization of the transport system, presenting a case study in Italy. The country has some peculiar features, such as several operating biogas plants, additional potential feedstock for biogas/biomethane generation, a well-developed natural gas network and established relevant natural gas uses in different final sectors, including transport. Based on current estimates for sustainable biomethane potential by 2030, ranging from 2.3 to 7.6 billion cubic meters depending on the scenario, the analysis compares technologies for the generation, distribution and final use of biomethane. The results of the analysis confirm the potential interesting contribution of biomethane in decarbonizing the Italian transport system: a billion cubic meters of biomethane can lead to 2.33–4.37 Mt CO 2 e savings, depending on the feedstock mix and the application. On a national basis, annual climate emission savings in 2030 range from 10.0 to 26.7 Mt CO 2 e , depending on the scenario. Additional 3.1–8.1 Mt CO 2 of emissions can be avoided if the CO 2 captured during the biomethane upgrading can be stored or reused. The proposed methodology could be used to extend the analysis to other countries, and to the European context. • We analyze the climate emissions of biomethane for different supply chains. • We evaluate the effects of feedstock, distribution strategy and electricity mix. • The results confirm the important role of biomethane for transport decarbonization. • We discuss the best allocation in transport segments based on emissions savings. • We compare alternative biomethane scenarios for Italy in 2030. [ABSTRACT FROM AUTHOR]

In recent times, electrification has become the most important means for decarbonization. One of the most pressing challenges to be addressed is the large-scale and long-term storage of electricity from renewable sources. By the utilization of the significant storage capacities of natural gas networks, power-to-methane technology using electrolysis offers the storage option most compatible with current electricity systems. Based on and complementing the IEA's hydrogen production database, the study compiled a database of power-to-methane projects launched globally between 2000 and 2020, also comparing these projects. The aim of the research was to examine the temporal and spatial distribution of international projects and their electrolysis technologies, types of methanation, carbon dioxide sources and utilizations of the final product. These analyses are important because it was these project factors, analyzed during the research, that best describe the synthetic methane production initiatives launched so far. The innovative importance of the research is that these aspects can be taken into account to establish the real contribution potentials of power-to-methane technology to decarbonization, especially in a changing policy and regulatory environment that seeks to accelerate its process. • Making global database of power-to-methane projects launched 2000-2020, analyzing 44 projects and comparisons (6 criteria). • They showed high spatial concentration but great heterogeneity in their temporal distribution and electrolysis technology. • The majority of the projects (72.7%) used chemical methanation and mostly biogas as a source of CO 2. • With an average electrolyzer power capacity of 0.49 MW, feeding in the natural gas grid was the most typical methane use. • In the future P2M technology may be important in decarbonization and help reach biogas and methane production goals. [ABSTRACT FROM AUTHOR]

• Government subsidies are vital to development of biomethane for pipeline addition. • Most changes to gas quality due to biomethane addition will be highly localized. • Regional biomethane availability is substantially affected by siloxane regulation. • Slightly relaxed heating value standards should not violate gas quality guidelines. Biomethane is a promising alternative fuel to mitigate the climate impacts arising from the natural gas sector. In California, several policies are in place to facilitate the development of biomethane. However, constraints on gas quality and gas properties can limit biomethane introduction into the gas pipeline. In this study, regional biomethane supplies and potential deviations in gas quality were assessed using steady-state simulation of natural gas pipeline networks at the zip-code scale under a variety of biomethane development scenarios and regulatory limits. Three regions of California – San Diego, Hanford, and South San Francisco bay area – were modeled. We explore local impacts to gas quality under various biomethane price scenarios and different levels of regulatory support. Across all regions, we do not find regional or local gas quality deviations to exceed interchangeability guidance with slightly relaxed biomethane heating value standards. Agricultural regions such as Hanford with high concentrations of dairy farms and low natural gas consumption may require pipeline upgrades to act as net exporters of biomethane. Regions with large seasonal variation in natural gas consumption may necessitate more stringent gas quality requirements to ensure safe combustion as gas composition varies across the year. High year-round demand for gas in urban regions will minimize gas quality deviation and could allow for case-by-case relaxation in gas quality requirements. We find that CO 2 and biofuel credits under state and federal regulations such as the California Low Carbon Fuel Standard (LCFS) and U.S. Renewable Fuel Standard (RFS) are vital to development of biomethane. With the incorporation of LCFS revenues, the portion of natural gas demands served by biomethane could be 4.3% in San Diego (5.2 bcf/y or 150 million m3/y), 54% in Hanford (2.66 bcf/y or 75.3 million m3/y), and 2.4% in the South Bay area (3.8 bcf/y or 110 million m3/y). Adding in current federal RFS credits, the biomethane supply only rises slightly in San Diego and South Bay Area but exceeds 100% of natural gas demand in Hanford (4.5 bcf/y or 130 million m3/y). [ABSTRACT FROM AUTHOR]

• Both CFD modelling and experiments optimized the mixing conditions in digesters. • The optimal mixing time was reduced to 2 mins/hr. • Intermittent mixing is an alternative strategy to reduce energy consumption. • Energy performance of an anaerobic digestion waste-to-energy system was simulated. • Intermittent mixing is efficient to generate sufficient biogas for net energy output. This study investigates the effect of different mixing strategies on anaerobic digestion of food waste in order to make the anaerobic digestion waste-to-energy process more energy efficient. Results showed that intermittent mixing is an alternative strategy to continuous mixing or unmixing for high efficient biogas production and energy saving. Through computational fluid dynamics modelling of fluid flow in anaerobic digesters, the mixing time was optimized to 2 mins/hr, at which point the reaction mixture is almost entirely homogeneous. The results of the model was validated with the experimental data. At an organic loading rate of 2.4 g VS FW /L/day, the semi-continuously mixed reactor maintains a higher specific methane yield of 437 mL CH 4 /g VS FW in comparison with the other controls. In addition, the semi-continuously mixed reactor has a larger proportion of Bacteroides and Methanocuelles. Based on the results of the bench scale experiment, the energy balance of the hybrid AD waste-to-energy system was simulated and evaluated. The calculated AD efficiency of the semi-continuously mixed reactor is 74.4%, which is higher than the AD efficiencies of the continuously mixed (66.9%) and unmixed reactors (14.9%). The energy balance investigated the electricity generated and the net heat output generated, in addition to self-sustaining and meeting the energy requirements of the various AD processes investigated. Based on the analysis, it was found the semi-continuous mixing is more energy efficient and sustainable to generate sufficient biogas output for the energy system to provide a net positive heat and electricity output. [ABSTRACT FROM AUTHOR]

• Novel simultaneous in-situ and ex-situ CO 2 biomethanisation demonstrated. • Biogas methane content over 95% achieved from conventional anaerobic digesters. • Volumetric methane production increased by more than 3-fold of its original value. • Upgrading biogas from multiple digesters in a single retrofitted digester. • CO 2 biomethanisation coupled AD bridges biomass and renewable energy industries. In-situ biomethanisation reduces the CO 2 in biogas to CH 4 via direct H 2 injection into an anaerobic digester, but volumetric methane production (VMP) is limited by organic loading. Ex-situ biomethanisation, where gaseous substrates are fed to pure or mixed cultures of hydrogenotrophic methanogens, offers higher VMP but requires an additional reactor and supply of essential nutrients. This work combined the two approaches in a novel hybrid application achieving simultaneous in-situ and ex-situ biomethanisation within an organically-loaded anaerobic digester receiving supplementary biogas. Conventional stirred-tank digesters were first acclimated to H 2 addition, increasing biogas methane content from 50% to 95% and VMP from 0.86 to 1.51 L L−1 day−1 at a moderate loading rate of 3 g organic chemical oxygen demand per L per day (g COD org L−1 day−1). Externally-produced biogas was then added to demonstrate simultaneous biomethanisation of endogenous and imported CO 2. This further increased VMP to 2.76 L L−1 day−1 without affecting organic substrate degradation. In-situ CO 2 reduction can alter digester pH by reducing bicarbonate buffering: the combined process operated stably at around pH 8.0 with 3–5% CO 2 in the headspace. Microbial community analysis indicated the process was mediated by bacterial syntrophic acetate oxidation and highly enriched hydrogenotrophic methanogenic archaea (up to 97% of the archaeal population). This approach presents the opportunity to retrofit a single digester for H 2 injection to convert and upgrade biogas from several others, minimising capital and operating costs by utilising both existing infrastructure and waste-derived feedstock nutrients for simultaneous biogas upgrading and power-to-methane. [ABSTRACT FROM AUTHOR]

• Conceptual design of power-to-methane with air or oxygen sweep for biogas upgrading. • Oxygen sweep by anode recirculation only marginally affects the system performance. • Most biogas-upgrading systems behave similarly to the standalone power-to-methane. • Internal methanation only beneficial at low voltage and high reactant utilization. • Adverse effect of internal methane reforming reduced by high utilization and pressure. Solid-oxide electrolyzer based power-to-methane is promising for large-scale energy storage as well as biogas upgrading by efficiently converting intermittent renewable power and CO 2 (e.g., in biogas) into synthetic methane. Either air or pure oxygen can be employed in solid oxide electrolyzers for anode sweeping and thermal management. This work investigates the optimal conceptual design of a variety of power-to-methane layouts to (i) identify the effect of sweep-gas type on system performance and (ii) compare different concepts for biogas upgrading. Bi-objective optimization is performed to understand the trade-off between system efficiency and methane production with the effects of the key design variables. The results indicate that oxygen sweep only marginally affected the system performance (6% reduction in methane production at the same system efficiency). The methanation inside the electrolyzer helped achieve a higher system efficiency (over 90%) by maintaining the electrolyzer temperature as high as possible. Unlike most biogas-upgrading systems, which behaved similarly to the standalone power-to-methane system, with an efficiency range of 70–86%, the direct-biogas-electrolysis performed within a wide efficiency range (52–88%) and a reduced methane yield (50% less than the other systems operating at 70% efficiency). The detrimental methane reforming inside the electrolyzer was limited by increasing the reactant conversion and the electrolysis pressure. The various solid-oxide electrolyzer based power-to-methane concepts showed promising results for biogas upgrading applications. The practical choice of biogas-upgrading concepts will depend on the requirement of operational flexibility to handle variable renewable power considering different gas storage and carbon capture technologies. [ABSTRACT FROM AUTHOR]

• The biological methanation was observed in a continuous long-term trickle bed process. • High product gas quality at c CH4,∅ = 96.6% at MFR max = 3.1 Nm3 CH4 /(m3·d) was reached. • After interruption and restart of input feeding, the same level performance was possible. • Inner pressure of p abs = 5 bar results in a MFR of 5.75 Nm3 CH4 /(m3·d) at c CH4,∅ = 97.7%. • Ex-situ methane enrichment of c CH4 = 50% to c CH4 > 94% could be shown. The recent increasing amount of energy from different renewable sources is connected to several challenges like flexible availability, secured energy supply, energy storage and its distribution. A suitable method is the sector coupling via conversion of excess renewable energy into natural gas by electrolysis followed by biological methanation of H 2 and CO 2. Gas quality, stability, controllability as well as low internal energy consumption and low technical effort of the process are of higher significance. Therefore, the biological methanation and methane enrichment by conversion of carbon dioxide and hydrogen were investigated in an anaerobic trickle bed process. In continuous long-term operation of 1200 days, a stable and significant high methane concentration of c CH4,∅ = 96.6% at methane formation rate of MFR max = 3.1 Nm3 CH4 /(m3·d) could be achieved. Process disturbance like interrupted availability of the input gases was examined and discussed. Methanation could be terminated and restarted almost immediately. Even after an interruption for a short (hours) or long (weeks) period, a performance at the same level was achievable. Therefore, process control is feasible. In a second and uncoupled investigation, the inner pressure was increased up to p abs = 25 bar. A pressure of p abs = 5 bar led to a maximum of MFR = 5.75 Nm3 CH4 /(m3·d) and c CH4,∅ = 97.7%. The higher pressure was harmful. Apart from pure carbon dioxide, biogas could also serve as a source of carbon, which enables an ex-situ methane enrichment of c CH4,∅ =50% to c CH4 > 94% and MFR max = 2.1 Nm3 CH4 /(m3·d) using the same process design without increased inner pressure. In particular, the high gas quality and process controllability cannot be found in comparable processes for biological methanation. Biogas for methane enrichment and CO 2 for methanation were accepted as carbon source. The high gas quality in the product reduces further effort of gas conditioning before injection into the natural gas grid. [ABSTRACT FROM AUTHOR]

• Catalytic direct methanation of biogas was demonstrated with real biogas. • Stable operation of the fluidised bed methanation for over 1100 h. • Biomethane with an average methane yield of 96% was injected into the gas grid. • Slow deactivation by organic sulphur compounds was identified and solved. • Experimental results were in accordance with results from a rate-based model. The catalytic direct methanation of biogas to produce biomethane was conducted in a pilot plant with real biogas from a biogas plant in Zurich. Stable operation of the methanation system including a bubbling fluidised bed could be demonstrated for over 1100 h of regular operation with subsequent injection into the gas grid. An average methane yield of 96% was reached. During the long-duration experiment, the slow deactivation process was monitored and found to be only moderate. Organic sulphur compounds could be identified as the main source of deactivation. However, deactivation from coking could not be fully excluded. With appropriate measures in the gas cleaning unit, so that no sulphur compounds were measured subsequently (limit of detection: <0.05 ppm of relevant components), the yield reduction went close to zero. Additionally, experimental results were compared to simulation results from a rate-based model presented elsewhere. Model predictions and experimental results are in accordance. The kinetics used in the rate-based model allowed a correct prediction of the optimum reaction temperature found by experimental results. [ABSTRACT FROM AUTHOR]

Highlights • Biological methanation was assessed in-situ and ex-situ. • A 24-hour batch ex-situ system produced 3.7 L CH 4 L VR −1 d−1 at 96% methane content. • High hydrogen loadings boost performance while adversely affecting efficiency. • Elevated hydrogen concentrations hamper in-situ acetogenesis process. • Concepts for full-scale methanation strategies are proposed to upgrade biogas. Abstract This study investigated in-situ and ex-situ biological methanation strategies for biogas upgrading potential. The addition and circulation of hydrogen with a ceramic gas diffuser unit revealed positive effects on the methanogenic process. A short-term maximum methane productivity of 2.5 L CH 4 per L reactor volume per day (L VR −1 d−1) was obtained in-situ. Adverse effects of elevated dissolved hydrogen concentrations on acetogenesis became evident. Ex-situ methanation in a reactor subjected to gas recirculation for recurrent 24 h periods achieved methane formation rates of 3.7 L CH 4 L VR −1 d−1. A biomethane with methane concentrations in excess of 96% successfully demonstrated the potential for gas grid injection. A theoretic model supplying gases continuously into a sequential ex-situ reactor system and steadily displacing the upgraded biogas confirmed similar methane formation performance and was advanced to a full-scale concept. Gas conversion efficiency of 95% producing biomethane at 85% methane content was attained. A hybrid model, where an in-situ grass digester is followed by an ex-situ reactor, is proposed as a novel upgrading strategy. [ABSTRACT FROM AUTHOR]

Highlight • A concentrating photovoltaic/thermal (C-PV/T) hybrid system is integrated in a biogas plant. • C-PV/T can partly provide the heat and electricity needed by biogas production and upgrading. • Integrating C-PV/T can achieve a positive net present value under the current market conditions. • The capital cost of C-PV/T, the interest rate and the biomethane price are the most critical factors. Abstract Biogas produced from anaerobic digestion processes is considered as an important alternative to natural gas and plays a key role in the emerging market for renewable energy. Aiming at achieving a more sustainable and efficient biomethane production, this work proposed a novel energy system, which integrates concentrating photovoltaic/thermal (C-PV/T) hybrid modules into a biogas plant with chemical absorption for biogas upgrading. The investigated energy system was optimized based on the data from an existing biogas plant, and its techno-economic feasibility was evaluated. Results show that about 7% of the heat consumption and 12% of the electricity consumption of the biogas plant can be covered by solar energy, by using the produced heat in a cascade way according to the operating temperature of different processes. The production of biomethane can also be improved by 25,800 N m3/yr (or 1.7%). The net present value of the integrated system is about 2.78 MSEK and the payback period is around 10 years. In order to further improve the economic performance, it is of great importance to lower the capital cost of the C-PV/T module. [ABSTRACT FROM AUTHOR]

Highlights • Direct use of renewable hydrogen and conversion to methane, methanol, or dimethyl ether. • Large-scale steady-state fuel production using carbon dioxide from biogas. • Simultaneous environmental, economic, and technical evaluation. • All four fuels enable significant greenhouse gas and pollutant reductions. • Combustion engine fuels considered result in similar emissions and costs. Abstract Hydrogen (H 2) production through water electrolysis is widely discussed as a means of storing renewable electricity in chemical bonds. Hydrogen can be used for transportation in fuel cell vehicles, but it can also be reacted with carbon dioxide (CO 2) to form other fuels. While many concepts have been proposed, detailed comparisons of different pathways are still scarce. Herein, we present a technical, environmental, and economic comparison of direct H 2 use in fuel cells, and production of methane, methanol, and dimethyl ether (DME) for use in internal combustion engines for light-duty vehicle applications. The scenario considered uses renewable electricity for water electrolysis, and CO 2 which is supplied continuously from biogas upgrading. All four fuels enable significant reductions (79–93%) in well-to-wheel greenhouse gas emissions as well as pollutant formation compared to fossil fuels, but they require very cheap H 2 to be competitive to fossil fuels, confirming intuitive expectations. While direct use of H 2 has obvious advantages (no conversion losses, high efficiency of fuel cells compared to internal combustion engines) in terms of overall electricity consumption, emissions, and fuel cost, its drawbacks compared to the other fuels are the need for an H 2 infrastructure, the high fueling pressure, and lower driving range. Among the three combustion engine fuels, DME has the lowest fuel cost and electricity consumption per distance driven because of the more efficient use of H 2 in its production, as well as the highest volumetric energy density, while methane has slightly lower greenhouse gas emissions. Cost and energy demand are dominated by H 2 supply, meaning that integrated solutions could be more attractive than separate electrolysis and fuel production. [ABSTRACT FROM AUTHOR]

Biogas upgrading is becoming essential in the valorization path for biogas. Biomethane from anaerobic digestion is identified to be one of the main resources to decarbonize the energy requirement. However, small-scale (especially farm-scale) applications suffer from a lack of implementation worldwide, mainly limited by the cost of the upgrading process. As one of the most used technologies, High Pressure Water Scrubbing presents a great margin for improvement. The most expansive items in this technology remain the packing column used for absorption and the stripping column used for water regeneration. In this work, the stripping column is replaced by a flash tank submitted to a rough vacuum (up to 0.2 bar in absolute pressure) associated to a static mixer to promote the gas desorption and thus the complete regeneration of the water. The implementation of an anisotropic packing, with properties evolving with the height of the column and adapted to the reduction of the gas flowrate due to absorption, is also investigated in order to reduce the size of the absorption column. A full-scale prototype was developed and implemented on a farm anaerobic digester. The range of application is from 20 to 40 Nm3/h of raw biogas. These field experiments associated to a complete description of the gas fluxes allowed to characterize the device in terms of carbon dioxide absorption efficiency, biomethane purity and methane recovery. Influences of six parameters (absorption pressure, desorption pressure, temperature, water flowrate, biogas flowrate, column height) were elucidated regarding those performances. Results highlight the great improvement of the water regeneration conducted under rough vacuum. From 0.8 to 0.2 bar in absolute pressure, the biomethane purity increased by 10%, the carbon dioxide elimination rate by 14%, and the methane recovery by 19%. With an increase in the packing height using an anisotropic configuration (modification of the packing properties with the column height) suited to the gas flowrate decrease into the column, a biomethane purity over 97% was obtained. The energy consumption associated was measured at 0.8 kWh / N m 3 of raw biogas but can be reduced to 0.3 kWh / N m 3. The overall energy efficiency for biogas upgrading can reach up to 91%. These results could pave the way for gas grid injection and vehicle fuel applications for small-scale anaerobic digestion. • Rough vacuum (0.8 to 0.2 bar) is applied to enhance water regeneration. • A full-scale prototype is set up and tested on a farm anaerobic digester. • Vacuum enhances water regeneration (+10% CH 4 purity) and methane recovery (+10%). • Anisotropic packing allows to reach high CH 4 purity over 97% for gas grid injection. • Energy efficiency is 91% for an electrical consumption of 0.38 kWh N m 3 . [ABSTRACT FROM AUTHOR]

Highlights • A new CCHP system based on biogas steam reforming is proposed for application. • Key process experiment of the reforming process validates the system feasibility. • Integrated performances are improved by synthetic use of biogas and solar energy. • Payback period of the new system reduces by 49.5% comparing to conventional ones. Abstract Anaerobic digesters should always be kept warm for a stable biogas yield. The conventional method for digester temperature maintenance results in a considerable waste of energy and pollution of the environment by directly firing biogas. Biogas-driven trigeneration systems can improve biogas utilization efficiency; however, the waste heat from the power engines is limited by the digester's thermal insulation, and additional fossil fuels are consumed to supplement the thermal power. To ease fossil fuel energy consumption and enhance the efficiency of biogas utilization, this paper presents a combined cooling heating and power (CCHP) system with synthetic use of biogas and solar energy. Solar energy is first transformed into syngas chemical energy through a chemical reaction called biogas steam reforming, and then the chemical energy is used for trigeneration in a conventional CCHP subsystem. Experimental research was conducted on the key process of biogas steam reforming to validate its feasibility. Hourly dynamic simulations of the proposed system were conducted by the mathematical models established using Lhasa, Tibet weather data. A biogas-fired CCHP system and a solar Dish/Stirling power system were adopted as reference systems, and a comparative analysis showed that the synthetic use of biogas and solar energy in the proposed system improves the annual electricity production by 8.70%, improves the refrigeration by 2.57%, and reduces the natural gas consumption by 8.66%. In addition, the direct CO 2 footprint in the proposed system is 8.20% lower than that in the reference systems. Finally, an economic study was conducted to validate the technical feasibility of the new system. The study offers a new method of using biogas and solar energy for an improved integrated performance. [ABSTRACT FROM AUTHOR]

Highlights • Thermophysical properties of dry/aqueous ChCl/Urea were surveyed and evaluated. • The database of ChCl/Urea and its aqueous were implemented into Aspen Plus. • The biogas upgrading using aqueous ChCl/Urea was simulated and evaluated. • Performances of aqueous ChCl/Urea scrubbing were compared with water scrubbing. Abstract Biogas has been considered as an alternative renewable energy, and raw biogas needs to be upgraded in order to be used as vehicle fuels or injected into the natural gas grid. In this work, the conceptual process for biogas upgrading using aqueous choline chloride (ChCl)/urea (1:2 on a molar basis) was developed, simulated and evaluated based on the commercialized software Aspen Plus. Reliable thermophysical properties and phase equilibria are prerequisite for carrying out process simulation. In order to carry out the process simulation, the thermophysical properties of ChCl/Urea (1:2) and its aqueous solutions as well as the phase equilibria of gas-ChCl/Urea (1:2), ChCl/Urea (1:2)-H 2 O and gas-ChCl/Urea (1:2)-H 2 O were surveyed and evaluated. After evaluation, the consistent experimental data of these thermophysical properties were fitted to the models embedded in Aspen Plus. The properties needed but without available experimental results were predicted theoretically. The Non-Random Two-Liquid model and the Redlich-Kwong equation (NRTL-RK) model were used to describe the phase equilibria. The equilibrium approach was used for process simulation. Sensitivity analysis was conducted to determine the reasonable operating parameters. With a set of reasonable operating conditions, the effects of ChCl/Urea (1:2) content on the total energy utilization, the diameters and pressure drops of absorber and desorber as well as the environmental assessment of the process were studied. The simulation results showed that, with the addition of ChCl/Urea (1:2), the total energy utilization decreased by 16% compared to the process with pure water, and the diameters of both absorber and desorber decreased with increasing content of ChCl/Urea (1:2). The process using aqueous ChCl/Urea (1:2) was more environmentally benign than that with pure water. Therefore, aqueous ChCl/Urea (1:2) is a promising solvent for biogas upgrading. [ABSTRACT FROM AUTHOR]

Highlights • Increasing the slurry to grass ratio improves sustainability of biogas. • Power to gas (P2G) can be used to upgrade biogas to biomethane. • The carbon intensity of hydrogen is higher than the electricity it is produced from. • P2G systems using the Irish electricity mix reduce sustainability of biomethane. • Renewable electricity levels of 85% allow biomethane be sustainable. Abstract The recast of the renewable energy directive (RED recast) considers power to gas (P2G) an advanced transport biofuel if a 70% greenhouse gas savings as opposed to the fossil fuel displaced is achieved. Power to methane systems can store electricity as gas and the system can be optimised in sourcing CO 2 from biogas to upgrade biogas to biomethane. The crucial question in this work is whether P2G systems can be sustainable and if they can improve the sustainability of biomethane systems using traditional upgrading systems. This work evaluates a comparative lifecycle assessment of grass and slurry (50:50 wet weight equivalent to 80:20 volatile solid weight) biomethane using P2G and/or amine scrubbing as an upgrading method. The sustainability of P2G upgrading systems is heavily dependent on the carbon intensity of the source of electricity. Using a 41% decarbonised electricity mix the sustainability was reduced using P2G and would not be deemed sustainable under criterion set by the RED recast. Maintaining a maximum of 2% fugitive CH 4 emissions, using 74% slurry (wet weight) in a grass slurry feedstock, allowing for 0.6 t carbon sequestration per hectare per annum in grasslands and using an electricity mix with 85% renewable electricity the whole system including P2G upgrading could satisfy the GHG savings of 70%. However, the traditional system employing amine scrubbing had higher levels of sustainability. [ABSTRACT FROM AUTHOR]

Highlights • Effect of CO 2 on the performance of CH 4 -fueled SOFCs was investigated. • Distribution of relaxation time for SOFCs operated under hydrocarbon was proposed. • Enhancement of performance was achieved by adding appropriate N 2 to fuel gas. Abstract Direct internal dry reforming is a promising way for solid oxide fuel cells (SOFCs) to directly use hydrocarbon fuels, since biogas already contains carbon dioxide and methane, which are both greenhouse gas contributing to global warming. In this paper, detailed experimental investigation and thermodynamic calculation were carried out to investigate the influence of CO 2 addition on fuel cell’s electrochemical characteristics and stability using CO 2 to CH 4 ratio ranging from 0 to 3. The maximum power densities were obtained at CO 2 to CH 4 ratios of 1.5 and 1.7 for fuel gas mixture with and without N 2 carrier gas, respectively. These two values are very close to thermodynamic calculation results about non-carbon limit. An analysis of distribution of relaxation time (DRT) for SOFC operated under dry reforming gas mixtures was first proposed in this study. The results show that the addition of CO 2 can significantly reduce both the anode activation polarization and the fuel gas diffusion resistance at low CO 2 to CH 4 ratio, while the influence became weaker at higher CO 2 to CH 4 ratio. An additional peak, with a larger relaxation time of 10−1 ∼ 101 s, was observed with dry reforming gas mixtures. This process, related to dry reforming reaction and water-gas shift reaction, was also influenced by the addition of CO 2. Besides, we observed an improvement of fuel cell performance by adding appropriate N 2 carrier gas to fuel gas, which may provide a new way to enhance the performance and durability of biogas-fueled SOFC. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The novel Ni-doped Sr 0.92 Y 0.08 TiO 3 was prepared via Pechini Method. • The novel Ni-doped Sr 0.92 Y 0.08 TiO 3 was activated under N 2 or reduction condition. • The N 2 -activated catalyst showed the better activity than the H 2 -activated case. • The 5 mol% Ni-doped Sr 0.92 Y 0.08 TiO 3 catalyst showed excellent long-term stability. Abstract In this study, novel perovskite-type Sr 0.92 Y 0. 08 TiO 3 -based catalysts were investigated for hydrogen production by the dry reforming of biogas (comprising CH 4 and CO 2 ). Ni-doped Sr 0.92 Y 0. 08 TiO 3 catalysts with improved catalytic activity were grown using the Pechini method. The prepared catalysts were characterized using X-ray diffraction to check for impurities introduced in the perovskite structure by doping method. The reforming of methane over perovskite-based catalysts has been extensively investigated; however, detailed understanding of the activating catalytic sites under different conditions is still lacking. To understand the details of the activating catalyst mechanism, transmission electron microscopy, temperature-programed reduction, X-ray photoelectron spectroscopic (XPS) analysis were performed under different activating conditions. XPS analysis of 5 mol% Ni-doped Sr 0.92 Y 0.08 TiO 3 revealed that the H 2 -activated catalyst lost active lattice oxygen sites and Ni sites due to formation of Ni hydroxide. Thus, the H 2 -activated catalyst has lower catalytic activity than the N 2 -activated one. [ABSTRACT FROM AUTHOR]

Biogas has been considered as an alternative renewable energy, and CO 2 removal from raw biogas (i.e. biogas upgrading) is needed for producing biomethane to be used as vehicle fuels or injected into the natural gas grid. Biogas upgrading with physical absorbents, such as water and other commercial organic solvents, is simple, efficient and with low energy requirements for regeneration. Recently, deep eutectic solvents (DESs) with nonvolatility, nonflammability and low price have been reported as promising alternatives to replace conventional physical absorbents in many research areas including biogas upgrading. However, the performances of these physical solvents including conventional physical absorbents and DES-based solvents have not been evaluated and compared with each other. In this work, the properties of 4 physical solvents (i.e. water, dimethyl ether of polyethylene glycol (DEPG), propylene carbonate (PC), and aqueous DES (AQ DES )) were compared. Furthermore, a conceptual process was developed to upgrade biogas with these solvents and simulated based on Aspen Plus in order to conduct performance comparison. The simulation results of energy utilization, the amount of recirculated solvents and the diameters of absorber and desorber were analyzed and compared based on equilibrium and rate-based approaches, respectively. The simulation results based on the rate-based approach were further used to estimate the costs of biogas upgrading process with a same raw biogas capacity for comparison. Meanwhile, the specific cost of biogas upgrading process with a same size of equipment was also evaluated. The results show that the CO 2 solubility, selectivity and viscosity are three more important properties, providing valuable information for developing novel physical solvents for CO 2 separation. The simulation results show that the equilibrium and rate-based approaches result in different conclusions, especially when the solvent viscosity is relatively high, and the rate-based approach is preferable. Based on the simulation results from the rate-based approach, the performances of AQ DES and PC are similar with a same amount of energy utilization, that is around 11% lower than water, and DEPG is inferior to water. For the case with the same gas capacity, the total annual costs of biogas upgrading process with these solvents show the following order: DEPG > AQ 60wt.%DES  > water > AQ 50wt.%DES  ≈ PC. For the case with the same size of equipment, compared to water, the total specific costs of biogas upgrading process with PC and AQ 50wt.%DES decrease by about 30% and 45%, respectively, and the treated biogas capacities increase to 1.5 and 2 times, respectively. In general, both PC and AQ 50wt.%DES show better performance than the other solvents. Considering that DES is an environmentally benign solvent, and the performance of DES can be greatly improved by further designing, it is more promising. [ABSTRACT FROM AUTHOR]

Farm operations in the USA and Europe have seen a radical change in the last decades: small sized farms are disappearing, and farm size and total livestock on larger farms are increasing. The resulting spatial density of animals causes several environmental impacts. Anaerobic digestion is one promising technical solution to alleviate most of these impacts while simultaneously providing a regional energy source. This analysis assesses the economic viability of using dairy-cow manure for either (i) the on-farm production and use of biogas to generate electricity and heat or (ii) the upgrading biogas to biomethane, a natural-gas substitute. A non-linear optimization model was developed to optimize plant capacity for anaerobic digestion and maximize the net present value for each option by farm size. In this study, we used Idaho‘s dairy farms as a case study. The analysis implies that at least 3000 cows per farm are required for an economically viable anaerobic-digestion plant operation. For farms with up to 3600 animals, the highest net present value was achieved for the on-farm use of biogas. Farms larger than that achieved their best economic results via the production of biomethane. In total about 45% of Idaho’s dairy manure could be utilized by economically feasible biogas and biomethane plants. A higher manure utilization rate could be achieved through joint, cooperative anaerobic digestion plants and manure transportation. The results can be transferred to other regions and countries, respectively, to reduce the negative impact of intensive livestock farming. [ABSTRACT FROM AUTHOR]

Heat prices are crucial for the revenues that biogas plants can generate; they can make or break a plant’s business. But little empirical price data exists. To remedy this and to identify factors influencing heat prices received by biogas plants, we surveyed 602 plant operators in Germany, yielding 1035 price points. We found a mean price of 1.91 EuroCt/kW h on the contract level, a mean revenue of 2.1 EuroCt/kW h on the plant level, and a wide variation in prices across utilization paths. Five factors were identified that together explain almost 50% of the price variance observed. The top three all contribute to higher prices: first, that the operator of the plant also operates the heat grid; second, that the heat contract offer full supply security; and third, that the heat be sold for heating buildings. Heat sold for agricultural drying processes commands significantly lower prices. Macroeconomic characteristics of a region do not affect prices; local factors seem to play the decisive role. This leads to wide price variations and the limited influence of any one factor on heat price. Companies and investors are thus advised to enter into pre-negotiations with prospective heat customers so that realistic site-specific numbers for off-heat prices can be used in planning; anything less puts a biogas venture at risk. Policy makers, when setting subsidies for biogas plants, also have to factor in revenues from heat; the results of this study can help them do so. [ABSTRACT FROM AUTHOR]

A system combining soil grown crops with photovoltaic panels (PV) installed several meters above the ground is referred to as agrivoltaic systems. In this work a patented agrivoltaic solar tracking system named Agrovoltaico®, was examined in combination with a maize crop in a simulation study. To this purpose a software platform was developed coupling a radiation and shading model to the generic crop growth simulator GECROS. The simulation was conducted using a 40-year climate dataset from a location in North Italy, rainfed maize and different Agrovoltaico configurations (that differ according to panel density and sun-tracking set up). Control simulations for an irrigated maize crop under full light were added to results. Reduction of global radiation under the Agrovoltaico system was more affected by panel density (29.5% and 13.4% respectively for double density and single density), than by panel management (23.2% and 20.0% for sun-track and static panels, respectively). Radiation reduction, under Agrovoltaico, affected mean soil temperature, evapotranspiration and soil water balance, on average providing more favorable conditions for plant growth than in full light. As a consequence, in rainfed conditions, average grain yield was higher and more stable under agrivoltaic than under full light. The advantage of growing maize in the shade of Agrovoltaico increased proportionally to drought stress, which indicates that agrivoltaic systems could increase crop resilience to climate change. The benefit of producing renewable energy with Agrovoltaico was assessed using the Land Equivalent Ratio, comparing the electric energy produced by Agrovoltaico cultivated with biogas maize to that produced by a combination of conventional ground mounted PV systems and biogas maize in monoculture. Land Equivalent Ratio was always above 1, it increased with panel density and it was higher with sun tracking than with static panels. The best Agrivoltaico scenario produced twice as much energy, per unit area, as the combination of ground mounted PV systems and biogas maize in monoculture. For this Agrivoltaico can be considered a valuable system to produce renewable energy on farm without negatively affecting land productivity. [ABSTRACT FROM AUTHOR]

Carbon dioxide and methane are two most important gases causing global warming; they are also the most crucial constituents in biogas. To efficiently convert the two greenhouse gases from biogas into synthesis gas (or syngas), the catalytic partial oxidation of methane (CPOM) triggered by a rhodium-based (Rh-based) catalyst in a spiral Swiss-roll reactor is studied. Three different biogases, including landfill, sewage, and farm biogases, are taken into consideration and the O 2 -to-CH 4 (O 2 /CH 4 ) molar ratio is between 0.6 and 0.7. It suggests that the reactor with heat recovery can substantially enhance the CH 4 conversion when compared with that without heat recirculation, and almost all CH 4 in the three biogases is converted. On account of certain amount of CO 2 contained in the biogases, the role played by dry reforming on CPOM is beyond those played by methane combustion and steam reforming. Within the investigated range of O 2 /CH 4 ratio, the maximum CO 2 conversion is 31.12%. The higher the CH 4 concentration and the lower the CO 2 one in a biogas, the better the H 2 and CO selectivity. The highest syngas yield is 2.80 mol/(mol CH 4 ), accounting for around 93% of theoretical result. Overall, the CH 4 conversion, H 2 yield, and H 2 /CO ratio in the product gas are higher than other studies, revealing that the excess enthalpy reactor is a promising device to simultaneously achieve syngas production and CO 2 utilization from biogas in industry. [ABSTRACT FROM AUTHOR]

CO 2 separation plays an important role in energy saving and CO 2 emission reduction to address global warming. Ionic liquids (ILs) have been proposed as potential absorbents for CO 2 separation, and a large amount of ILs have been synthesized to achieve this purpose. To screen ILs for CO 2 separation, CO 2 absorption capacity/selectivity and energy use have been considered, whereas the required amount of IL has been seldom involved. In this work, CO 2 separation from biogas with 30 conventional ILs was analyzed theoretically on the basis of the Gibbs free energy change combining the amount of IL needed and the energy use. The desorption temperature was estimated from the absorption pressure, and then the amount of IL needed and the energy use were calculated. Thermodynamic analysis shows that the absorption pressure and the desorption temperature need to be changed to achieve optimal separation. Several ILs were screened with certain criteria, namely, the amount of IL needed and energy use. The performance of the screened ILs was compared with that of commercial CO 2 absorbents (30 wt% MEA, 30 wt% MDEA, DEPG, and water). The comparison with DEPG and water shows that the screened physical ILs are promising for IL-based technologies because of their advantages of negligible vaporization enthalpy, low amount of absorbent needed, or low energy use. A comparison with 30 wt% MEA and 30 wt% MDEA indicates that chemical IL has negligible vaporization enthalpy and low energy use. These findings show that the screened ILs are promising for CO 2 separation from biogas. [ABSTRACT FROM AUTHOR]

A successful transition towards a cleaner and more sustainable energy management in 2050 requires the implementation of renewable energy sources on a large scale. Therefore, it is expected that the share of renewable energy will further increase. Due to the introduction of these intermittent energy sources, the need for flexibility in our energy system increases significantly. Power-to-gas (P2G) is one promising option for providing long term energy storage and for providing flexibility to the electricity system. An interesting, recent technological development is biological methanation. The latter utilizes microorganisms to catalyze the Sabatier reaction. This biological reaction can be achieved at lower temperatures and pressures than when a chemical catalyst is used and has a higher tolerance to contaminations from the CO 2 source, process upset or contamination by foreign organisms. We investigate the techno-economic potential of biological methanation (i.e. microbial power-to-gas concept) using a case study that revolves around anaerobic digestion using mainly municipal organic waste in Belgium. The most important parameters that influence the economic feasibility are the electricity consumption (44%), operating hours of the electrolyser (14%), and the investment cost of the electrolyser (14%). Based on our findings we offer further routes of research that serve to strengthen the business case. [ABSTRACT FROM AUTHOR]

Syngas and biogas are two typical biofuels generated from biomass wastes through gasification and anaerobic digestion processes, which are considered to be the future fuels for IC engines. In this work, the utilization of biogas and syngas produced from horticultural waste in a premixed spark ignition engine was investigated. An experimentally validated KIVA4-based CFD simulation integrated with CHEMKIN was performed to evaluate engine performance fuelled by syngas and biogas under both single and blended-fuel modes. Effects of ignition timing, hydrogen content in syngas and methane content in biogas on both energetic and environmental performance have been studied. The indicated thermal efficiency (ITE) of syngas fueled engine at wide open throttle (WOT) condition under maximum brake torque (MBT) operation was found to be higher than that of biogas fueled engine, meanwhile, with much lower NOx emission. In addition, a comparison of the engine performance between the single and blended-fuel modes under different syngas mixing ratios was conducted in terms of ITE and NO X emission. The results suggest that the utilization of syngas and biogas under blended-fuel mode can not only maintain the MBT energetic performance under single-fuel mode, but also show its potential in reducing NOx emission and lessening the tendency of knock onset. [ABSTRACT FROM AUTHOR]

Wastewater treatment plants (WWTP) are currently very energy and greenhouse gas intensive processes. An important opportunity to reduce both of these quantities is via the use of biogas produced within the treatment process to generate energy. This paper studies the optimal energy and economic performance of a wastewater treatment facility fitted with a solid oxide fuel cell (SOFC) based combined heat and power (CHP) plant. An optimisation framework is formulated and then applied to determine cost, energy and emissions performance of the retrofitted system when compared with conventional alternatives. Results show that present-day capital costs of SOFC technology mean that it does not quite compete with the conventional alternatives. But, it could become interesting if implemented in thermally-optimised WWTP systems. This would increase the SOFC manufacturing volumes and drive a reduction of capital and fixed operating costs. [ABSTRACT FROM AUTHOR]

Anaerobic digestion systems on dairy farms in New York State rely on gate-fee revenues from co-digestion to ensure economic viability. Yet, because gate fees are paid on a volumetric (or weight) basis, farmers have been compelled to accept large waste volumes. When these wastes are co-digested at rates exceeding the design capacity of the digester, potentially significant technical, environmental, and economic consequences may arise. To better understand these trade-offs, we performed a combined environmental life-cycle and economic assessment with uncertainty analysis. We used the Anaerobic Digestion Model #1 to simulate the co-digestion process for 10 potential co-substrates that were hypothetically mixed with dairy manure throughout a range of loading rates. These simulation results demonstrated the need to include a robust anaerobic digestion model to capture complex process dynamics and loading limits. Results also showed that while higher loading rates were more economically favorable, they caused considerable reductions in the degree of waste stabilization during the digestion process, which dramatically increased downstream methane emissions ( e.g., >450%) on the farm compared to manure-only digestion. Regardless, most co-digestion scenarios led to a net reduction in total life-cycle emissions compared to manure only and not digesting the co-substrate due mainly to greater electric power production and synthetic fertilizer replacement. Economically, gate-fee revenue was the most important contributor to profitability, substantially outweighing the revenue from electric power production, while also compensating for the increased handling costs of the added waste volume. Ultimately, the model clearly demonstrated the important environmental and economic implications arising from current anaerobic digestion implementation practices and policy in New York State. In addition, the model highlighted key stages in the system life-cycle, which was used to instruct and recommend immediately actionable policy changes. [ABSTRACT FROM AUTHOR]

Captured biogas produced within wastewater treatment facilities can be the remedy to offset its increasing energy requirements. Furthermore, the conversion of methane to methanol is quite attractive as it is more transportable and has higher energy yield. Methane can be utilized by methanotrophs in which methanol is produced as a metabolic intermediate. Compared to type II, type I methanotrophs are more advantageous due to its higher growth yields and energy efficiency. This work objective is to optimize methanol bio-production using type I methanotrophs enriched from activated sludge process. This study demonstrates methanol production using mixed culture from wastewater sludge. Optimization of methanol dehydrogenase inhibitors, sodium formate, and copper concentrations, as well as, the gaseous headspace composition and biomass density resulted in a significant enhancement in methanol production. The maximum methanol concentration achieved in this study was 485 ± 21 mg/L. Whereas, the highest methanol productivity obtained was equal to 2115 ± 81 mg/L/day. Those findings show the high potential of producing methanol using mixed culture enriched from activated sludge process. [ABSTRACT FROM AUTHOR]

In this study, an approach to optimize the components and operation of biogas plant systems, which temporarily stores biogas in floating-drum biogas storage tank (BS) and feeds in a semi-continuous manner, was developed. First, the parameters of biogas production and consumption were characterized into mathematical models, and estimated with a 1-year operating data set of a village-scale biogas plant (fermentation volume, 80 m 3 ). Then, the established models, which included biogas production and consumption rates, were used to determine the optimal BS volume and operation parameters for improving biogas plant performance. In contrast to the biogas usage level achieved with the established BS (76.4%), that obtained with an optimal system could reach up to 85.7% and the feeding frequency for a 1-year operation could be decreased 6.5 times. Our proposed approach exhibited a number of attractive features, including accurate determination of parameters, reduced biogas emission, and cost efficiency, which may not only enhance biogas benefits, but also increase economic and environmental feedback on village-scale biogas plant operation. [ABSTRACT FROM AUTHOR]

For bioenergy installations producing heat, the minimum required GHG savings will be 85% from 2026. This is significant and a considerable challenge for biogas systems. This paper investigates use of biogas from pig farms at a nearby milk processing facility, a large energy user. The paper examines minimisation of greenhouse gas (GHG) associated with plant layout and in particular in transporting slurry by road to a large centralised anaerobic digestion (CAD) facility or transporting biogas by low pressure pipe from decentralised anaerobic digestion (DAD) at the pig farms. In detail four scenarios were assessed: “CAD1” road transport of slurry to a CAD located at the biogas end user (milk processing facility); “CAD2” transport of biogas by pipeline from an optimally located CAD located a distance from the biogas end user; “DAD1” DAD with biogas transportation in a biogas pipe network; and “DAD2” DAD with biogas transportation via a biogas pipe network of minimum length to reduce cost. Scenario CAD2 (transporting biogas by pipe from optimally located CAD) reduced CO 2 eq emissions associated with the road haulage of pig slurry by 51% compared to CAD1 (transporting slurry by road to a CAD at the milk processing facility) and 7% overall. Scenario DAD1 (distributed biogas production in DAD and transportation of the biogas by pipe) was shown to be the best scenario with CO 2 eq emissions reduction of 19% compared to Scenario CAD1 (road transport of slurry with CAD at the biogas user). Scenario DAD2 (distributed biogas production in DAD while minimising length of the biogas network) reduced CO 2 eq emissions by 18% relative to scenario CAD1, reduced the network length by 34% compared to scenario DAD1 but increasing total CO 2 eq emissions by 1% compared to Scenario DAD1. [ABSTRACT FROM AUTHOR]

Issues related to SOFCs performance and durability are strictly dependent on the feeding fuel quality. SOFC capability to be fed with fuels different from hydrogen opens to scenarios in which a big variety of fuels can be used at the aim. Unfortunately, problems related to anode deactivation due to the contaminants presence can arise. The present work investigates the performance of anode supported solid oxide fuel cells in case of co-feeding of different trace compounds. Electrochemical impedance spectroscopy is the investigation technique used to analyze the impedance spectra. Typical biogas from OFMSW trace contaminants that follow an initial failure in the cleaning system, such as sulphur, aromatic compounds and siloxanes, have been simultaneously tested. Tests showed that the most deleterious impact for the SOFC was due to the H 2 S action. This influences mostly the electrochemical losses respect to diffusion losses, even if this last are not null and can be accounted as a secondary effect. On the contrary, the co-presence of D4 and H 2 S mitigates in the short-term the effect that the only D4 produces when fed with biogas. The most relevant consequence produced by C 7 H 8 was recorded in the low frequency of Nyquist plot, affecting mainly the mass transport phenomena. Experimental tests are accompanied by the implementation of the fuel cell model through COMSOL Multiphysics software to study the effect of pollutants on fuel cell performance. [ABSTRACT FROM AUTHOR]

Biogas is a renewable energy source that can be used either directly or through various pathways (e.g. upgrading to bio-methane, use in a fuel cell or conversion to liquid fuels) for heat, electricity generation or mechanical energy for transport. However, although there are various options for biogas utilization, there is limited guidance in the literature on the selection of the optimum route, and comparison between studies is difficult due to the use of different analytical frameworks. The aim of this paper was to fill that knowledge gap and to develop a consistent framework for analysing biogas-to-energy exploitation routes. The paper evaluated 49 biogas-to-energy routes using a consistent life cycle analysis method focusing on energy efficiency as the chosen crtierion. Energy efficiencies varied between 8% and 54% for electricity generation; 16% and 83% for heat; 18% and 90% for electricity and heat; and 4% and 18% for transport. Direct use of biogas has the highest efficiencies, but the use of this fuel is typically limited to sites co-located with the anaerobic digestion facility, limiting available markets and applications. Liquid fuels have the advantage of versatility, but the results show consistently low efficiencies across all routes and applications. The energy efficiency of bio-methane routes competes well with biogas and comes with the advantage that it is more easily transported and used in a wide variety of applications. The results were also compared with fossil fuels and discussed in the context of national policies. This research resulted in the development of a flexible framework for comparing energy efficiencies which can provide the basis for further research on optimizing the sustainability of biogas-to-energy systems across a range of indicators. [ABSTRACT FROM AUTHOR]

The anaerobic digestion of source-separated organic waste is a mature and increasingly used process for biomethane production. However, the efficient use of different fractions of waste is a big concern in anaerobic digestion plants. This study proposes the use of a new process configuration that couples the anaerobic digestion of biodegradable waste with the pyrolysis of lignocellulosic or green waste. The biochar obtained from pyrolysis was added to a digester as an adsorbent to increase the biomethane content and to support the development of a stable microbial community. In addition, the bio-oil and syngas produced by the pyrolysis process were reformed into syngas and then converted to biomethane via methanation. Modelling and simulations were performed for the proposed novel process. The results showed an approximately 1.2-fold increase in the biomethane volume produced. An overall efficiency of 67% was achieved, whereas the stand-alone anaerobic digestion system had an efficiency of only 52%. The results also indicated a high annual revenue for the integrated process compared to that for an alternative treatment (incineration) of green waste. [ABSTRACT FROM AUTHOR]

This study aimed at assessing the impact of ultrasonication on the anaerobic digestibility of thickened waste activated sludge (TWAS) in an anaerobic fluidized bed reactor (AnFBR). Two lab-scale AnFBRs treating TWAS were studied to explore the impact of ultrasonication (US) in the dispersing and reuse of scum for methane production. Our current work applied ultrasound energy at 120–600 kJ/d for 2 s per 30 s corresponding to ultrasonication densities of 6–15.7 MJ/kg dry-scum-d. At an organic loading rate (OLR) of 5.1 kg COD/m 3 -d and US energy of 11.9 MJ/kg dry-scum-d, scum decreased by 82% from 20.2 gm/d to 3.7 gm/d, and COD and VSS destruction efficiencies were 65% and 63%, respectively roughly 20% higher than the control reactor without US. Scum reduction varied linearly with US energy about 25 kJ/g TS was required to break the scum. The energy balance also indicated that the aforementioned US energy of 11.9 MJ/kg dry-scum-d was optimum because of energy neutrality. Specific methanogenic activity (SMA) tests showed that the activity-based sludge retention time (SRT) is higher for the ultrasonicated AnFBR (U-AnFBR) (7.1 days) compared to AnFBR (5.1 days). Furthermore, a higher rate of maximum specific biogas production (R m ) was observed in the U-AnFBR of 26.7 ml/gmVSS-hr as compared to 15.7 ml/gmVSS-hr for the control AnFBR, with respective suspended biomass activities of 2 ml/gmVSS-hr and 4.1 ml/gmVSS-hr i.e. confirming that US improved methanogenic activity in the reactor and reduced the detachment of active methanogens. [ABSTRACT FROM AUTHOR]

Previous life cycle assessments for agro-bioenergy production rarely considered some agronomic factors with local and regional impacts. While many studies have found the environmental and socio-economic impacts of producing bioenergy on arable land not good enough to be considered sustainable, others consider it still as one of the most effective direct emission reduction and fossil fuel replacement measures. This study improved LCA methods in order to examine the individual and combined effects of often overlooked agronomic factors (e.g. alternative farm power, seed sowing, fertilizer, tillage and irrigation options) on life-cycle energy indicators (net energy gain-NEG, energy return on energy invested-EROEI), across the three major agro-climatic zones namely tropic, sub-tropic and the temperate landscapes. From this study, we found that individual as well as combined effects of agronomic factors may improve the energy productivity of arable bioenergy sources considerably in terms of the NEG (from between 6.8 and 32.9 GJ/ha to between 99.5 and 246.7 GJ/ha for maize ethanol; from between 39.0 and 118.4 GJ/ha to between 127.9 and 257.9 GJ/ha for maize biogas) and EROEI (from between 1.2 and 1.8 to between 2.1 and 3.0 for maize ethanol, from between 4.3 and 12.1 to between 15.0 and 33.9 for maize biogas). The agronomic factors considered by this study accounted for an extra 7.5–14.6 times more of NEG from maize ethanol, an extra 2.2–3.3 times more of NEG from maize biogas, an extra 1.7 to 1.8 times more of EROEI from maize ethanol, and an extra 2.8–3.5 times more of EROEI from maize biogas respectively. This therefore underscores the need to factor in local and regional agronomic factors into energy efficiency and sustainability assessments, as well as decision making processes regarding the application of energy from products of agro-bioenergy production. [ABSTRACT FROM AUTHOR]

Biogas has been earmarked as an efficient way to promote economic development and mitigate environmental emissions, and it requires a better accounting framework to evaluate its performance. In this study, we aim to develop an emergy-based accounting framework to assess and report the sustainability performance of biogas projects. First, the existing financial accounting and environmental accounting methodologies are combined to measure and report the economic events and environmental characteristics of a biogas project. Then, using the new metric of Emdollar value, the cost and revenue flows within the system boundary are unified and quantified by multiplying specific emergy transformity to reflect their embodiment and hierarchical characteristics. An integrated accounting framework covering economic aspects (economic profitability, economic efficiency, operation risk), environmental aspects (environmental resource utilization, load, emissions) and environmental-economic composited characteristics (emissions reduction efficiency, Emdollar intensity of emission reduction, emission intensity of profit) is set up accordingly. Results show that the biogas project has a positive net present value of 1.64E+04 Emdollars. The total cost can be returned after 5 years. The renewability ratio, environmental load ratio (ELR), and composite sustainability indicator (CSI) reflecting environmental load are 9%, 10.1, and 0.76, respectively. The proposed sustainability accounting framework may unveil the real environmental support and assess the ecological economic performance of a biogas project. [ABSTRACT FROM AUTHOR]

The increasing population living in cities is leading to higher resource utilization, which strains the cities’ ability to focus on sustainability. Adoption of different technologies can transform cities into “smart cities” that utilize energy in a more efficiently. This paper presents results from a technology assessment tool developed together with six mid-sized European cities. The main areas of focus have been evaluated based on the cities’ priorities: transportation (both public and private) and consumers’ perspectives on the use of smart electricity meters. The use of electric vehicles in Sweden, and a techno-economic evaluation of biogas-derived biomethane and electricity use in public transportation have been analyzed. The main conclusions show an overall higher efficiency for biogas-derived electricity use in electric buses; a need for higher consumer engagement through more detailed information provision for both increasing EV market penetration and electricity savings; and a need to establish detailed technology assessments for successful technology adoption in cities. [ABSTRACT FROM AUTHOR]

To decrease the use of fossil fuels and face the energetic demand, the integration of renewable energy is a necessary step. Part of this renewable energy can be supplied by the production of electricity from photovoltaic panels and windfarms. The massive use of these intermittent energies will lead to overproduction periods, and there is consequently a need to convert this surplus of electricity into a storable form of energy. Power-to-gas (PtG) technology consists in using electricity to convert water into hydrogen by electrolysis, and then to synthetize methane from carbon dioxide and hydrogen. Techno-economic and Life Cycle Assessment of methane production via the combination of anaerobic digestion and PtG technology have been applied to sewage sludge valorization. Process studies and equipment design have been addressed considering already available technologies. Sensitivity analyses have been done on biogas upgrading technologies, electricity prices, annual operation time and composition of the electricity mix with also a comparison between PtG and direct injection. It appears that the more the electricity is expensive, the longer the operation time of the methanation process must be to be competitive with injection of methane from biogas. Reduction of electricity consumption of the electrolysis step decreases production costs. Even if the current context does not feature adapted conditions to ensure an economically viable chain, the evolution of the energetic context in the next few years as well as the expected technological improvements will contribute to overall cost reduction. From an environmental point of view, continuous PtG generates more greenhouse gases than direct injection, but intermittent operation with use of renewable electricity can significantly reduce GHG emissions. From an endpoint impacts perspective, impact from continuous PtG are higher than biogas upgrading, but much lower than fossil energy. Future development of low electricity consumption of the electrolysis process, and integration of renewable credits from CO 2 valorization can increase the competitiveness of this technology. [ABSTRACT FROM AUTHOR]

A unique cogeneration system integrating a biogas fed Solid Oxide Fuel Cell (SOFC) and a Concentrating Solar Thermal (CST) system for a reference Waste Water Treatment Plant (WWTP) in Italy is proposed. Biogas – which is locally in the WWTP from the anaerobic digestion (AD) of the collected sludge – can be used to produce electricity using SOFC power modules. The thermal power recovered from the SOFC exhaust stream is used to meet part of the digester thermal load. However, the rest heat loads are provided by using the integration with the CST system and an auxiliary boiler. Energy analysis is performed to determine the effect of using the solar heating system on the system performance. Also, the economic performance is evaluated through a cash-flow analysis and the calculation of the Levelized cost of electricity (LCOE). It is observed that installing 300 m 2 , 700 m 2 , 1100 m 2 of solar collectors could cover 8%, 18% and 30% of total digester heat load, respectively. Results show an overall beneficial effect of the solar installation, both from an energy and economic standpoint of view. For all the scenarios analyzed, the LCOE is lower than the grid electricity price and, with increasing solar integration, the value is further reduced showing that, despite the investment return time, the electricity production during the entire system lifetime is competitive against grid electricity prices. [ABSTRACT FROM AUTHOR]

This study investigates the feasibility of using an electrochemical process to convert excess renewable electricity and biogas into hythane gas, which has higher value than biogas and can be stored and transported using current natural gas infrastructure. The electrochemical process utilizes the protons generated in water electrolysis to liberate cations in silicate minerals, which in turn forms metal hydroxide and efficiently captures the CO 2 present in biogas. The H 2 produced in electrolysis is blended with purified biogas to generate mixed hythane product, which has a higher combustion rate in methane fueled vehicles. Results show that under a voltage of 3.5–4.0 V, the system reduced CO 2 in biogas from the original 40% to less than 15% and increased the heat value of the gas product from 534 kJ/mol to over 669 kJ/mol. Preliminary techno-economic analysis showed a net profit of $0.28 per thousand ft.cu hythane generated when standard grid electricity is used, and the profit may be increased by orders of magnitude if excess renewable electricity is used. The process offers a new route for renewable energy storage and upgrade. [ABSTRACT FROM AUTHOR]

Three landfill gas (LFG) valorization technologies were compared using energy and exergy efficiency and a streamlined Life-Cycle Assessment (LCA) method. The technologies were (i) steam reforming and hydrogen utilization in an in situ cogeneration fuel cell (SR-IS-FCC), (ii) biogas utilization in an in situ gas engine cogeneration plant (IS-GEC), and (iii) amine scrubbing and biomethane utilization in an ex situ gas engine cogeneration plant (AS-ES-GEC). The SR-IS-FCC alternative recorded the highest exergy efficiency and savings in cumulative energy demand (CED), and the lowest global warming potential (GWP) when all the heat is utilized in situ; otherwise, the highest exergy efficiency and the lowest GWP and CED were associated with the AS-ES-GEC alternative. The results indicate that AS-ES-GEC is the preferential choice when heat cannot be utilized in situ. Otherwise, SR-IS-FCC records the best values for the three criteria, and the AS-ES-GEC technology is the least interesting alternative. [ABSTRACT FROM AUTHOR]

We report an energy-efficient biogas reforming process with high and stable methane conversions by O 2 presence. During this biogas reforming process, the effects of various O 2 concentrations in biogas on initial conversions and stability at various temperatures on a Ni/SiO 2 catalyst were detailed investigated. In addition, theoretical energy consumption and conversions were calculated based on the Gibbs energy minimization method to compare with experimental results. Carbon formation and sintering during the reforming process were characterized by thermal gravity analysis, the Brunauer-Emmett-Teller method, X-ray diffraction, and high-resolution transmission electron microscopy to investigate the feasibility of applying this process to an inexpensive nickel catalyst. The results showed that 5% O 2 in biogas improved the CH 4 conversion and stability of biogas reforming. The enhancement of stability was attributed to the inhibited sintering, our first finding, and the reduced carbon deposition at the same time, which sustained a stable conversion of CH 4 , and proved the applicability of base Ni catalyst to this process. Higher O 2 concentrations (⩾10%) in biogas resulted in severe decrease in CO 2 conversion and greater H 2 O productivity. Our proposed biogas reforming process, with a high and stable conversion of CH 4 , reduced energy input, and the applicability to inexpensive base metal catalyst, offers a good choice for biogas reforming with low O 2 concentrations (⩽5%) to produce syngas with high energy efficiency. [ABSTRACT FROM AUTHOR]

[Display omitted] • DES-HTD was evaluated for co-production of biodiesel and biogas from microalgae. • DES increased NER from 0.65 to 0.83 due to dramatically increased energy consumption. • DES recovery is critical to reduce energy consumption of DES-HTD for fuel production. • Low NER of 0.58 along with negative net GHG emissions were achieved via DES recovery. A life-cycle assessment was carried out to evaluate the industrial feasibility of deep eutectic solvents (DES) for microalgae pretreatment. The effects of DES on hydrothermal disintegration (HTD) of microalgae for biodiesel and biogas co-production was assessed in terms of net energy ratio (NER, Energy input/Energy output) and greenhouse gas (GHG) emissions. Although the addition of DES during HTD increased the energy output by 36.33 %, the NER increased from 0.65 to 0.83 due to the larger increase in energy input. The increase in energy input is because DES synthesis consumed a lot of energy, accounting for 45.93 % of the total energy input. The addition of DES also increased the net GHG emissions from −25.53 g CO 2-eq MJ−1 to 26.04 g CO 2-eq MJ−1. It is essential to reduce the GHG emissions and energy consumption via DES recovery for commercial applications. When DES was recovered by a combined method of membrane filtration and recrystallization, a low NER of 0.58 along with negative net GHG emissions were achieved for microalgal biofuel production via DES-HTD. [ABSTRACT FROM AUTHOR]

This study introduces a new approach to estimate biomethane market potential by analysing biogas markets and their relative environmental and economic advantages. This potential is then combined with greenhouse gas emission values for different feedstock shares (farm-fed and waste-fed systems) and different application share to determine the possible contribution of biomethane to national greenhouse gas emission saving goals. Markets that are considered are Germany and the UK being the biggest emitters of CO 2eq in the European Union. The current use was compared with the scenarios (i) market projection, derived from literature study and (ii) reasonable potential, derived from environmental and economic calculations. The current market status is presented to show the past market development until the present date and associated greenhouse gas savings. Additionally the potential of biomethane to contribute to greenhouse gas emission savings is extensively described. Results indicate that the share of application in Germany is more environmental beneficial than the one in the UK achieving higher greenhouse gas savings at comparable feed-in level. In contrast, the UK has a higher share of waste-fed systems to produce biomethane. The use of biomethane in CHP plants achieves the highest GHG emission savings and if organic waste is used as feedstock the possible savings are even higher. With an increase of biomethane used in CHP plants and a decrease of biomethane used for direct heating the savings in the UK could increase up to 52%. Current savings of 2446 kt CO 2eq (Germany) and 606 kt CO 2eq (UK) can be extended to 4483 kt CO 2eq (Germany) and 1443 kt CO 2eq (UK) respectively. Scenario results were determined based on the environmental and economic advantageousness development of the existing biogas market. In this way positive future market development as well as improved shares of feedstock and application can contribute to further greenhouse gas emission savings of Germany and the UK. [ABSTRACT FROM AUTHOR]

A techno-economic analysis was conducted to assess the feasibility of using forestry residues with different bark contents for bioethanol production. A proposed cellulosic ethanol biorefinery in Sweden was simulated with Aspen Plus. The plant was assumed to convert different forestry assortments (sawdust and shavings, fuel logs, early thinnings, tops and branches, hog fuel and pulpwood) to ethanol, pellets, biogas and electricity. The intention was not to obtain absolute ethanol production costs for future facilities, but to assess and compare the future potential of utilizing different forestry residues for bioethanol production. The same plant design and operating conditions were assumed in all cases, and the effect of including bark on the whole conversion process, especially how it influenced the ethanol production cost, was studied. While the energy efficiency (not including district heating) obtained for the whole process was between 67 and 69% regardless of the raw material used, the ethanol production cost differed considerably; the minimum ethanol selling price ranging from 0.77 to 1.52 USD/L. Under the basic assumptions, all the forestry residues apart from sawdust and shavings exhibited a negative net present value at current market prices. The profitability decreased with increasing bark content of the raw material. Sensitivity analyses showed that, at current market prices, the utilization of bark-containing forestry residues will not provide significant cost improvement compared with pulpwood unless the conversion of cellulose and hemicellulose to monomeric sugars is improved. [ABSTRACT FROM AUTHOR]