Showing papers on "Biogas published in 2021"

Pretreatment of lignocelluloses for enhanced biogas production: A review on influencing mechanisms and the importance of microbial diversity

Abstract: As one of the most efficient methods for waste management and sustainable energy production, anaerobic digestion (AD) countenances difficulties in the hydrolysis of lignocelluloses biomass. Different pretreatment methods have been applied to make lignocelluloses readily biodegradable by microorganisms. These pretreatments can affect biogas yield by different mechanisms at molecular scale, including changes in chemical composition, cellulose crystallinity, degree of polymerization, enzyme adsorption/desorption, nutrient accessibility, deacetylation, and through the formation of inhibitors. The present article aims at critically reviewing the reported molecular mechanisms affecting biogas yield from lignocelluloses via different types of pretreatments. Then, a new hypothesis concerning the impact of pretreatment on the microbial community developed (throughout the AD process from an identical inoculum) was also put forth and was experimentally examined through a case study. Four different leading pretreatments, including sulfuric acid, sodium hydroxide, aqueous ammonia, and sodium carbonate, were performed on rice straw as model lignocellulosic feedstock. The results obtained revealed that the choice of pretreatment method also plays a pivotally positive or negative role on biogas yield obtained from lignocelluloses through alteration of the microbial community involved in the AD. Considerable changes were observed in the archaeal and bacterial communities developed in response to the pretreatment used. Sodium hydroxide, with the highest methane yield (338 mL/g volatile solid), led to a partial switch from acetoclastic to the hydrogenotrophic methane production pathway. The findings reported herein undermine the default hypothesis accepted by thousands of previously published papers, which is changes in substrate characteristics by pretreatments are the only mechanisms affecting biogas yield. Moreover, the results obtained could assist with the development of more efficient biogas production systems at industrial scale by offering more in-depth understanding of the interactions between microbial community structure, and process parameters and performance.

Current status of biogas upgrading for direct biomethane use: A review

Abstract: Anaerobic digestion produces biogas, a mixture of CH4 and CO2, where CH4 is a low cost, environmentally friendly, and renewable energy source. The application of biogas production is increasing rapidly as a means of reducing the pollution impact of organic biomasses. However, biogas contains unwanted elements such as hydrogen sulfide, carbon monoxide, siloxanes, and carbon dioxide. To remove these elements, several biogas upgrading technologies like water scrubbing, amine scrubbing, pressure swing adsorption, and membrane separation have been developed and are being used at various commercial scales. Problems with these methods are high energy consumption, the use of expensive chemicals, and high operating cost. Therefore, a major effort is currently underway to improve the design of existing methods as well as developing innovative new upgrading technologies such as cryogenic separation and biological upgrading. This review intends to provide a comprehensive overview of the limitations with the existing upgrading technologies along with recent advances in physical, chemical, and biological biogas upgrading technologies (e.g., pressure swing adsorption, membrane separation, biochar adsorption and CO2 conversion by biological organisms) and further into possible future solutions, such as hybrid systems. Comparative studies of process complexities and associated economic concerns are also provided, and future perspectives that may facilitate research into sustainable biogas upgrading technologies are discussed, focusing in particular on cryogenic separation, novel biological techniques, biochar based upgrading and hybrid technologies incorporating two or more different methods seamlessly integrated.

Recent advances in bio-based carbon materials for anaerobic digestion: A review

Abstract: In recent years, the great interest in improving anaerobic digestion (AD) process resulted in the use of different types of additives or accelerants to exploit several profitable synergies, including improved CH4 yield and digestate quality. However, the use of carbon-based materials also reduces operational instability and substrate-induced inhibition that hinder microbial breakdown activity of the organic matter. In this review, recent advances made by different research groups in order to enhance the performance of AD system are reviewed, emphasizing the utilization of low-cost carbon-based materials in the AD process, with a particular focus on the use of bio-based carbons such as biochar, activated carbon, and carbon cloth. The bio-based carbons in AD system support bacterial syntrophy and accelerate to direct interspecies electron transfer (DIET), and enhance methane yield. Moreover, this review gives emphasis on the fabrication of bio-based carbon materials and their applications as additives and their working mechanism in the AD system. Finally, this manuscript debates optimized AD technology to enhance biogas yield via bio-based carbons for energy production and sustainable environment for betterment of human health.

Biomass in biogas production: Pretreatment and codigestion

Abstract: Globally, there is increasing awareness that the implementation of ‘waste to energy’ technology is one of the best means to achieve sustainable energy development. The most popular approach is the conversion of organic-rich compounds into clean and renewable products by anaerobic digestion (AD). Biogas can be produced from agricultural residues, municipal/industrial biowastes, and sustainable biomass, especially materials that are locally available. However, in many cases, the methane yields obtained from the conventional AD process are regarded as having limited profitability. This paper summarizes the recent knowledge regarding the different strategies that are used to enhance AD efficiency and the methods to strengthen the existing incentives to overcome today's barriers to biogas production. Special attention was given to several approaches used to improve the biodegradability of organic matter and the methane potential of feedstocks, mainly codigestion and pretreatment of single/mixed substrates. The statistical analyses indicated enormous variability among biogas systems, thus, there is a need for unification of the methods applied for process control and the parameters used for the discussion of results. A synchronized methodology is also needed to understand the environmental advantages and drawbacks of selected utilization pathways in biogas production. Currently, the underestimated potential of AD is of growing interest, and pretreatment/codigestion can directly increase the effectiveness of this technology and lead to its optimization. Nonetheless, a proper evaluation of the environmental (e.g., sustainable biomass) and social (e.g., bioaerosol nuisance) aspects is also needed.

Upgrading biogas into syngas through dry reforming

Abstract: Biogas is comprised of two major compounds (i.e., CH4 and CO2) derived from fermentation of organic wastes. Therefore, biogas can be used as a source for the generation of syngas (H2 and CO: through dry reforming of methane). Given that the dominant fraction of biogas is consumed as a feedstock for lower-end products, such as heat and power, dry reforming can be used as an effective option for the valorization of biogas. In this review, we offer up-to-date knowledge on the development of biogas dry reforming in the context of the effects of the composition of the biogas, reaction conditions, and impurities in the biogas. Theoretical estimations of biogas compositions were made along with the compositional matrix of organic substrates. The thermodynamic calculations of dry reforming were also described with other side reactions. In conclusion, the challenges and the potential future directions of this research field were given to help open up new paths toward hybrid biological/chemical processes for H2 production.

Biogas-to-biomethane upgrading: A comparative review and assessment in a life cycle perspective

Abstract: The study reviews and compares the most utilised techniques to obtain high quality biomethane by upgrading biogas from anaerobic digestion of the organic fraction of municipal solid waste. Environmental and economic aspects of membrane separation, water scrubbing, chemical absorption with amine solvent, and pressure swing adsorption have been quantified in a life cycle perspective. An attributional environmental Life Cycle Assessment has been implemented with the support of a Material Flow Analysis and in combination with a complementary environmental Life Cycle Costing. The analyses are based on data largely obtained from Italian existing plants but they can be generalised to the whole European Union, as demonstrated by a companion sensitivity analysis. The comparative assessment of the results indicates all the examined options as fully sustainable, also identifying the “win-win” situations. In particular, the membrane separation technique appears to have the best performances, even though in some cases with limited differences. With reference to base case scenarios, this technique shows better results for the respiratory inorganics potential (up to 34%, i.e. up to 328 kgPM2.5eq/y), global warming potential (up to 7%, i.e. up to 344 tCO2eq/y), and non-renewable energy potential (up to 12%, i.e. up to 6400 GJprimary/y) as well as for life cycle costs (up to 3.4%, i.e. about 60 k€/y). The performances of the examined techniques appear anyway dependent on site-specific conditions (such as the injection pressure in the gas grid or the existence/amount of local economic incentives) and commercial strategies for the market of interest.

A review of recent developments in application of low cost natural materials in purification and upgrade of biogas

Abstract: The main contaminants in biogas namely carbon dioxide, hydrogen sulfide, and siloxanes limit its application especially in engines by reducing energy density and causing corrosion on machine parts. Furthermore, the carbon dioxide in biogas contributes highly to global warming. Therefore, biogas should be upgraded to increase its safe application. Most commercial methods of biogas cleaning are expensive for small and medium scale digesters. There is no review documentation detailing the usage of natural materials in the purification of biogas. The aim of the current study was to systematically and critically review recent developments in the applications of natural materials in the purification and upgrade of biogas. Documented literature indicate that the low-cost natural adsorbents have potential in purification of biogas. The adsorption capacity of biogas contaminants for most materials can be enhanced by physical and chemical activation. The two mechanisms through which these material eliminate carbon dioxide in biogas namely surface adsorption and wet carbonation process have been discussed. In addition, the study looked at the factors that affect the removal of carbon dioxide from biogas using natural materials. The adsorption capacity of biogas contaminants for different natural and modified materials were reviewed. Furthermore, a summary of the merits and demerits of different natural adsorbents for biogas purification is presented. Future studies should investigate the methane loss during upgrading process using low-cost adsorbents. Comparative investigations of the process cost-effectiveness of using natural materials to upgrade biogas should be carried out to determine their suitability against the commercial processes.

Optimization of Hydrolysis-Acidogenesis Phase of Swine Manure for Biogas Production Using Two-Stage Anaerobic Fermentation

Abstract: The traditional pig manure wastewater treatment in Taiwan has been low in methane production efficiency due to unstable influent concentration, wastewater volume, and quality. Two-stage anaerobic systems, in contrast, have the advantage of buffering the organic loading rate in the first stage (hydrolysis-acidogenesis phase), allowing a more constant feeding rate to the second stage (methanogenesis phase). Response surface methodology was applied to optimize the operational period (0.5–2.0 d) and initial operational pH (4–10) for hydrolysis and acidogenesis of the swine manure (total solid 5.3%) at 35 °C in batch operation mode. A methanogenesis verification experiment with the optimal condition of operational period 1.5 d and pH 6.5 using batch operation resulted in peak volatile acid production 7 g COD/L, methane production rate (MPR) 0.3 L-CH4/L-d, and methane yield (MY) 92 mL-CH4/g-CODre (chemical oxygen demand removed). Moreover, a two-stage system including a hydrolysis-acidogenesis reactor with the optimal operating condition and a methanogenesis reactor provided an average MPR 163 mL/L-d and MY 38 mL/g volatile solids, which values are 60% higher than those of a single-stage system; both systems have similar dominant methane-producing species of Firmicutes and Bacteroidetes with each having around 30%–40%. The advantages of a two-stage anaerobic fermentation system in treating swine manure for biogas production are obvious.

A critical review of biogas production and usage with legislations framework across the globe

Abstract: This review showcases a comprehensive analysis of studies that highlight the different conversion procedures attempted across the globe. The resources of biogas production along with treatment methods are presented. The effect of different governing parameters like feedstock types, pretreatment approaches, process development, and yield to enhance the biogas productivity is highlighted. Biogas applications, for example, in heating, electricity production, and transportation with their global share based on national and international statistics are emphasized. Reviewing the world research progress in the past 10 years shows an increase of ~ 90% in biogas industry (120 GW in 2019 compared to 65 GW in 2010). Europe (e.g., in 2017) contributed to over 70% of the world biogas generation representing 64 TWh. Finally, different regulations that manage the biogas market are presented. Management of biogas market includes the processes of exploration, production, treatment, and environmental impact assessment, till the marketing and safe disposal of wastes associated with biogas handling. A brief overview of some safety rules and proposed policy based on the world regulations is provided. The effect of these regulations and policies on marketing and promoting biogas is highlighted for different countries. The results from such studies show that Europe has the highest promotion rate, while nowadays in China and India the consumption rate is maximum as a result of applying up-to-date policies and procedures.

Biogas as an energy vector

Abstract: Biogas is a sustainable energy vector with diverse input sources (e.g. landfills and anaerobic digestion of waste materials, wastewater treatment sludge, manure from animal production, or energy crops) and diverse applications. The nature of the substrate and the design of the biogas production process determines the composition of raw biogas. All types of biogas must be cleaned and upgraded before delivering to the consumers and in practice, the key challenge of the biogas supply chain is its cleaning and upgrading to consumers quality. The physicochemical technologies used to clean and upgrade the raw biogas are reliable, mature and at high technology readiness levels. This paper critically reviews the biogas supply chain including feedstock supply, biogas production and upgrading/cleaning processes, potential hazards of biogas contaminants, product specification based on applications, and biogas/biomethane uses. The biogas cleaning and upgrading technologies with emphasis on cost comparison are assessed. In summary, the upgrading technology alternatives and their associated costs are found substantially affected by the project-specific circumstances. For instance, upgrading with chemical scrubbing might be preferred in the availability of cheap on-site thermal energy. If the biomethane is planned to be injected into high-pressure natural gas pipelines, those upgrading methods operating at relatively high pressures (e.g. membranes) would be preferred. If the biomethane injection point to the gas grid is located distant from the production site, the distribution cost will also play a determinative role in the overall biogas supply chain economics. Among all these factors, plant capacity seems to be a pivotal element in the economics of biogas supply chain. Amendments to national and sub-national support schemes are also an important factor affecting investment decisions.

Biogas production from small-scale anaerobic digestion plants on European farms

Abstract: Small-scale anaerobic digestion (SSAD) is a promising technology for the treatment of livestock manure and the organic fraction of municipal wastes, especially in low population communities or in stand-alone waste treatment facilities. SSAD systems can transform organic matter into biogas (a mixture, mainly composed of carbon dioxide and methane), making the technology suitable for a variety of applications in energy, agriculture and, potentially, the emerging bio-products and bio-processes sector. Small-scale farming processes can further exploit the portable and flexible options made available by implementing SSAD systems to effect on-demand conversion of organic waste streams to useful heat (and, potentially, electricity), with significant economic benefits accruable (especially when such energy carriers are exported). SSAD is particularly applicable to the European agricultural sector, where the average individual farm sizes and land productivities are currently insufficient to meet the feedstock requirements of medium and large-scale plants. Despite the apparent benefits of SSAD, the technology is still not well utilised. Much of the research previously conducted has focused on large-scale systems. This study explores the current status of SSAD technology in Europe by identifying process design and operational characteristics, influential EU policies, the recent progress related to SSAD, and the issues encountered. The study sheds light on an area with limited research by providing an overview of the technology's present status in Europe by identifying areas of future study.

Integral use of orange peel waste through the biorefinery concept: an experimental, technical, energy, and economic assessment

Abstract: This work aims to evaluate from an energy and economic perspective the production of essential oil, pectin, and biogas as alternatives to valorize orange peel waste. For this, the chemical characterization, extraction of essential oil, and pectin of industrial of this residue samples were done. Moreover, the remaining solid was used to produce biogas. The experimental results were used as input data to simulate the biorefinery. The mass and energy balances from the simulation were used to perform energy and economic analysis of the biorefinery system analyzing the net present value and processing scale as determining factors. Also, mass and energy efficiency indicators were applied to evaluate the performance of the biorefinery. The experimental essential oil, pectin extraction, and biogas yields 0.61% w/w (wet basis), 10.35% w/w (wet basis), and 89.39 Nm3/ton OPW mL biogas/g VS with a CH4 content of 66.73% (59.6 Nm3/ton OPW), respectively. The mass and energy indicators show a good performance of the process in terms of mass and energy efficiency indicators. Moreover, the economic analysis leads to observe that the proposed biorefinery is only feasible at low processing scales. In a conclusion, orange peel waste is a potential feedstock to obtain value-added products such as essential oil and pectin and energy vectors such as biogas in an energy and economic feasible way at low scales allowing the implementation of small-scale integrated biorefinery systems.

Hydrogen-Enriched Biogas Premixed Charge Combustion and Emissions in Direct Injection and Indirect Injection Diesel Dual Fueled Engines: A Comparative Study

Abstract: This paper presents a comparative study on combustion and emissions of hydrogen-enriched biogas premixed charge direct injection dual-fuel (DIDF) engine and indirect injection dual-fuel (IDIDF) engine. The results show that the IDIDF engine outperforms the DIDF engine in terms of higher indicative engine cycle work (Wi) and lower emissions of CO, soot, and noise, but the disadvantage is higher NOx emission. Under the same fueling condition, the IDIDF engine’s Wi is on average 6% higher than that of the DIDF engine, but the NOx concentration in the combustion products of the IDIDF engine is 1.5 times higher than that of the DIDF engine. The IDIDF engine creates the stratified mixture distribution with higher O2 concentration in the auxiliary combustion chamber, which is favorable for auto-ignition and reduces the ignition delay. The biogas composition affects slightly CO and soot emissions, but significantly affects NOx emission. When the methane composition in biogas increases from 60% to 80%, the soot volume fraction is approximately 0.1 ppm in both types of combustion chambers, the CO concentration varies from 1.4% to 1.8%, and the NOx concentration varies from 3000 to 5000 ppm in the case of IDIDF engine and 2500–4500 ppm in the case of DIDF engine. For both types of dual-fuel engines, when engine speed increases, CO concentration and the soot volume fraction increase, while Wi and NOx concentration decrease.