Yazar "Kumar, Gopalakrishnan" seçeneğine göre listele

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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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    A novel Microcystis aeruginosa supported manganese catalyst for hydrogen generation through methanolysis of sodium borohydride
    (Pergamon-Elsevier Science Ltd, 2020) Duman, Fatih; Atelge, M. R.; Kaya, Mustafa; Atabani, A. E.; Kumar, Gopalakrishnan; Sahin, U.; Unalan, S.
    In this study, Microcystis Aeruginosa (MA)- microalgae species was used for the first time as a support material with metal ions loading to fabricate a highly efficient catalyst for the hydrogen generation through methanolysis of sodium borohydride (NaBH4). Microalgae was pre-treated with hydrochloric acid (3 M HCl) for 24 h at 80 degrees C. Subsequently, different metal ions (Mn, Co, and Mo) were loaded to the pre-treated samples. Finally, metal-loaded samples were subjected to burning in oven to fabricate the catalyst. Primarily, manganese metal was selected based on the best metal performance. Afterwards, different metal loading ratios, burning temperatures and burning times were evaluated to synthesize the optimal MA-HCl-Mn catalyst. Results showed the optimal conditions as Mn ratio, burning temperature and time as 50%, 500 degrees C and 45 min, respectively. To characterize the catalyst, FTIR, SEM-EDX, XRD, XPS and TEM analyses were performed. Hydrogen generation via methanolysis was performed at various NaBH4 ratio of 1-7.5% while changing concentrations from 0.05 to 0.25 g catalysts with diverge temperatures of (30, 40, 50 and 60 degrees C). The maximum hydrogen generation rate (HGR) by this novel catalyst was found as 4335.3, 5949.9, 7649.4 and 8758.9 mLmin(-1)gcat(-1), respectively. Furthermore, the activation energy was determined to be 8.46 kJ mol(-1). (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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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.
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    Spent coffee grounds anaerobic digestion: Investigating substrate to inoculum ratio and dilute acid thermal pretreatment
    (Elsevier Sci Ltd, 2023) Semaan, Georgeio; Atelge, M. R.; Cayetano, Roent Dune; Kumar, Gopalakrishnan; Kommedal, Roald
    Spent coffee grounds have the potential of being used in further bioprocesses to produce materials and fuels. In Norway, the relative abundance and ease of collection of this waste substrate make it a candidate for investi-gation. For this study, the substrate-to-inoculum ratio as well as a combined dilute acid-thermal pretreatment were assessed by a series of biochemical methane potential assays using spent coffee grounds as a substrate. Reactors with substrate-to-inoculum ratio 2 demonstrated a relatively low hydrolysis rate constant (kh) and comparatively high volatile fatty acids/alkalinity concentrations rendering them inapt to produce bio-CH4. Pretreatment was conducted over varying contact times (15-45 min), dilute acid concentrations (1.5-2.5 %, v/ v), and liquid-to-solid ratios (10-20 %, v/w) and evaluated using response surface methodology. To determine bio-CH4 yield, pretreatment time and the interaction between acid concentration and liquid-to-solid ratio are considered significant variables, suggesting a shared importance. Chemical oxygen demandremoval is primarily contingent upon changes in liquid-to-solid ratio. Finally, Fourier-transform infrared spectroscopy of the dis-carded solid phase showed that the major functional groups are still widely present in the coffee grounds even after pretreatment was applied. A better understanding of the biodegradability profile of spent coffee grounds as a function of substrate-to-inoculum ratio is achieved.