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    A Critical Overview of the State-of-the-Art Methods for Biogas Purification and Utilization Processes
    (Mdpi, 2021) Atelge, Muhamed Rasit; Senol, Halil; Djaafri, Mohammed; Hansu, Tulin Avci; Krisa, David; Atabani, Abdulaziz; Eskicioglu, Cigdem
    Biogas is one of the most attractive renewable resources due to its ability to convert waste into energy. Biogas is produced during an anaerobic digestion process from different organic waste resources with a combination of mainly CH4 (similar to 50 mol/mol), CO2 (similar to 15 mol/mol), and some trace gasses. The percentage of these trace gases is related to operating conditions and feedstocks. Due to the impurities of the trace gases, raw biogas has to be cleaned before use for many applications. Therefore, the cleaning, upgrading, and utilization of biogas has become an important topic that has been widely studied in recent years. In this review, raw biogas components are investigated in relation to feedstock resources. Then, using recent developments, it describes the cleaning methods that have been used to eliminate unwanted components in biogas. Additionally, the upgrading processes are systematically reviewed according to their technology, recovery range, and state of the art methods in this area, regarding obtaining biomethane from biogas. Furthermore, these upgrading methods have been comprehensively reviewed and compared with each other in terms of electricity consumption and methane losses. This comparison revealed that amine scrubbing is one the most promising methods in terms of methane losses and the energy demand of the system. In the section on biogas utilization, raw biogas and biomethane have been assessed with recently available data from the literature according to their usage areas and methods. It seems that biogas can be used as a biofuel to produce energy via CHP and fuel cells with high efficiency. Moreover, it is able to be utilized in an internal combustion engine which reduces exhaust emissions by using biofuels. Lastly, chemical production such as biomethanol, bioethanol, and higher alcohols are in the development stage for utilization of biogas and are discussed in depth. This review reveals that most biogas utilization approaches are in their early stages. The gaps that require further investigations in the field have been identified and highlighted for future research.
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    A critical review of pretreatment technologies to enhance anaerobic digestion and energy recovery
    (Elsevier Sci Ltd, 2020) Atelge, M. R.; Atabani, A. E.; Banu, J. Rajesh; Krisa, David; Kaya, M.; Eskicioglu, Cigdem; Kumar, Gopalakrishnan
    Biogas production from different waste resources still has limitations due to its complex structure and slowly biodegradable nature. To improve methane yield and anaerobic digestion performance, various substrate pretreatment methods have been suggested. This paper reviews the latest trends, progress, and research achievements about pretreatment technologies to improve anaerobic digestion efficiency. The pretreatment techniques are divided into four main groups which are physical, chemical, biological, and combined. The effect of inhibitor formation during the pretreatment process is discussed. The energy performance, economics, and environmental impact of these pretreatment technologies are revealed. This study concludes with future trends and emphasizes the necessity of pretreatment methods.
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    Anaerobic co-digestion of oil-extracted spent coffee grounds with various wastes: Experimental and kinetic modeling studies
    (Elsevier Sci Ltd, 2021) Atelge, M. R.; Atabani, A. E.; Abut, Serdar; Kaya, M.; Eskicioglu, Cigdem; Semaan, Georgeio; Lee, Changsoo
    The effect of oil extraction from spent coffee grounds as a pre-treatment strategy prior to anaerobic digestion besides assessing the feasibility of defatted spent coffee grounds co-digestion with spent tea waste, glycerin, and macroalgae were examined. Mesophilic BMP tests were performed using defatted spent coffee grounds alongside four co-substrates in the ratio of 25, 50, and 75%, respectively. The highest methane yield was obtained with the mono-digestion of defatted spent coffee grounds with 336 +/- 7 mL CH4/g VS and the yield increased with the increase in the mass ratio of defatted spent coffee grounds during co-digestion. Moreover, defatted spent coffee grounds showed the highest VS and TS removal at 35.5% and 32.1%, respectively and decreased thereafter. Finally, a linear regression model for the interaction effects between substrates was demonstrated and showed that distinctly mixing defatted spent coffee grounds, spent coffee grounds, and spent tea waste outperforms other triple mixed substrates.
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    Carbon molecular sieve production from defatted spent coffee ground using ZnCl2 and benzene for gas purification
    (Elsevier Sci Ltd, 2020) Kaya, M.; Atelge, M. R.; Bekirogullari, M.; Eskicioglu, Cigdem; Atabani, A. E.; Kumar, Gopalakrishnan; Yildiz, Y. S.
    The aim of the current study is to manufacture molecular sieve from the defatted spent coffee ground. The defatted spent coffee ground for the specified particle size (100 mu m) was chemically activated with different agents (ZnCl2, H3PO4, KOH) and then carbonized at different temperatures (400-900 degrees C). A thorough characterization of the produced activated carbon was performed and activated carbons with the highest BET surface area were subsequently used to produce carbon molecular sieve. The surface modification was performed with benzene vapor at different temperatures (600-900 degrees C) and different combustion times (30-90 min.). In addition to the BET analysis, SEM, TGA and FT-IR analysis were also undertaken. The results obtained through characterizations showed that the pore diameters of carbon molecular sieve produced from defatted spent coffee ground varied from 2 to 4 angstrom. To conclude, the results suggest that the fabricated carbon molecular sieve can be used for the removal of impurities such as CH4, CO2, NOx and other impurities in natural and biogas considering the porosity of the sieves.