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.

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

Membrane engineering: Latest advancements in gas separation and pre-treatment processes, petrochemical industry and refinery, and future perspectives in emerging applications

Multidimensional approaches of biogas production and up-gradation: Opportunities and challenges.

Biogas is one of the promising renewable energy sources that successfully implemented at domestic and industrial scales. This work presents a preliminary evaluation of the role and contribution of biogas as a sustainable energy source towards achieving the sustainable development goals (SDGs). This work summarizes the common feedstock and impurities in the biogas as well as the advantages and disadvantages of biogas compared with fossil fuels. Challenges and barriers associated with biogas production in developing and developed countries were elaborated and connected with SDGs. Finally, the relation between the circular economy, biogas, and related SDGs was presented. The biogas has been found to have direct impacts and contributions to 12 out of the 17 SDGs. The main contributions of the biogas come from its ability to increase renewable energy, reduce climate change, enhance the waste management process, and create jobs. A set of 58 indicators was provided as a guideline for the stakeholders within the biogas industry to extend the benefits of the biogas toward the achievement of the SDGs and minimize any possible trade-off. The results of this work will help the different players within the biogas industry to form policy to ensure that biogas contribution to the SDGs is maximized. 

Biogas role in achievement of the sustainable development goals: Evaluation, Challenges, and Guidelines

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.

Upgrading biogas into syngas through dry reforming

The environmental impacts and high long-term costs of poor waste disposal have pushed the industry to realize the potential of turning this problem into an economic and sustainable initiative. Anaerobic digestion and the production of biogas can provide an efficient means of meeting several objectives concerning energy, environmental, and waste management policy. Biogas contains methane (60%) and carbon dioxide (40%) as its principal constituent. Excluding methane, other gasses contained in biogas are considered as contaminants. Removal of these impurities, especially carbon dioxide, will increase the biogas quality for further use. Integrating biological processes into the bio-refinery that effectively consume carbon dioxide will become increasingly important. Such process integration could significantly improve the sustainability of the overall bio-refinery process. The biogas upgrading by utilization of carbon dioxide rather than removal of it is a suitable strategy in this direction. The present work is a critical review that summarizes state-of-the-art technologies for biogas upgrading with particular attention to the emerging biological methanation processes. It also discusses the future perspectives for overcoming the challenges associated with upgradation. While biogas offers a good substitution for fossil fuels, it still not a perfect solution for global greenhouse gas emissions and further research still needs to be conducted.

Technologies for Biogas Upgrading to Biomethane: A Review.

Carbon dioxide is the most influential gas in greenhouse gasses and its amount in the atmosphere reached 412 µmol/mol in August 2020, which increased rapidly, by 48%, from preindustrial levels. A brand-new chemical industry, namely organic chemistry and catalysis science, must be developed with carbon dioxide (CO2) as the source of carbon. Nowadays, many techniques are available for controlling and removing carbon dioxide in different chemical processes. Since the utilization of CO2 as feedstock for a chemical commodity is of relevance today, this study will focus on how to increase CO2 solubility in culture media used for growing microbes. In this work, the CO2 solubility in a different medium was investigated. Sodium hydroxide (NaOH) and monoethanolamine (MEA) were added to the culture media (3.0 g/L dipotassium phosphate (K2HPO4), 0.2 g/L magnesium chloride (MgCl2), 0.2 g/L calcium chloride (CaCl2), and 1.0 g/L sodium chloride (NaCl)) for growing microbes in order to observe the difference in CO2 solubility. Factors of temperature and pressure were also studied. The determination of CO2 concentration in the solution was measured by gas analyzer. The result obtained from optimization revealed a maximum CO2 concentration of 19.029 mol/L in the culture media with MEA, at a pressure of 136.728 kPa, operating at 20.483 °C.

Amir Izzuddin Adnan

Papers

Technologies for Biogas Upgrading to Biomethane: A Review.

Determination of Dissolved CO2 Concentration in Culture Media: Evaluation of pH Value and Mathematical Data