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    Combined biofuel production from cotton stalk and seed with a biorefinery approach
    (Springer Heidelberg, 2020) Uyan, Merve; Alptekin, Fikret Muge; Bastabak, Benginur; Ozgul, Sevim; Erdogan, Baris; Ogut, Tuba Ceren; Celiktas, Melih Soner
    Due to usage of fossil fuels, the depletion of world crude oil reserves and increased deteriorating climate conditions have reached a high level. These circumstances have led researches to search for alternative and efficient fuels. the main biofuels considered are bioethanol and biodiesel. in this study, ethanol and biodiesel production from cotton stalk and seed were aimed using liquid hot water (LHW) along with consecutive processes, where separate saccharification and fermentation (SHF) process was carried out. the maximum ethanol concentrations of 0.348 g/L and 0.721 g/L were achieved at 24 h and 72 h, respectively. For biodiesel conversion, cottonseed oil was subjected to transesterification, where the main interest was to utilize the by-product, glycerol. Three different glycerol concentrations were investigated in terms of ethanol fermentation using Escherichia coli K1 active culture. the maximum ethanol concentration of 0.415 g/L was achieved at 20 mL glycerol concentration for 48 h. Overall, cotton stalk and seed have the potential to be utilized on an industrial scale.
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    Comparative analysis of the effect of cell immobilization on the hydrogenothrophic biomethanation of CO2
    (Wiley Periodicals, Inc, 2021) Daglioglu, Tugce; Ogut, Tuba Ceren; Ozdemir, Guven; Azbar, Nuri
    Carbon capture and utilization (CCU) has been offered as a potential technological solution for mitigating the greenhouse gas emissions and climate change concern worldwide. Anaerobically carbon utilization has started to be in the agenda of researchers in recent years since this approach offers significant advantages such as use of catalysis reactions through environmentally friendly microorganisms under low temperature and pressure operational conditions. Moreover, a cleaner and more effective bioenergy production is realized in the form of biomethane. This study aimed to exploit the merits of cell immobilization in order to provide a stable hydrogenotrophic biomethanation process. For this purpose, two different immobilized bioreactors packed with plastic moving bed biofilm reactor (MBBR) and glass beads packing materials were comparatively investigated. To the best of our knowledge, these two immobilization materials were used for the first time for this purpose. Two different bioreactor configurations were compared for the performance parameters such as methane formation rate, H-2 consumption and methane contents in the headspace. Methane content in the headspace of these bioreactors were measured to be 80 and 75% for MBBR bioreactor and glass bead bioreactors, respectively. in addition, methane formation rates (MFR) of 5.14 and 4.8 m(3)/m(3)/day were achieved in MBBR and glass beads bioreactors, respectively. Even though both bioreactor configurations performed highly efficient biomethanation of CO2, the statistical evaluation of the results indicated that MBBR performance was more favourable for hydrogenotrophic biomethanation. (c) 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.
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    The effect of various thermochemical pretreatment methods on the biomethanisation of hemp (Cannabis sativa) hurd and kinetic analysis
    (Springer Heidelberg, 2022) Aric, Alpcan; Karagoz, Sadik Can; Ogut, Tuba Ceren; Daglioglu, S. Tugce; Duman, Gozde; Yanik, Jale; Azbar, Nuri
    In this study, the effects of different pretreatment methods on the biochemical methane potential (BMP) of hurds from two hemp species, namely Narlisaray (NS) and Futura 75 (F), were investigated. The effect of pretreatment on BMP was discussed on the basis of the change in the chemical constituents of the raw material. The highest BMP yields of 272 mL CH4/g VS (F) and 218 mL CH4/g VS (NS) were obtained when the combined alkaline and thermal pretreatment was applied which resulted in the highest amount of hemicellulose degradation. (143% for alkaline and 74% for thermal, respectively, higher than those from raw hurds). It was found that BMP yields and the efficiency of pretreatment for two hemp species depended on genotypes, not on the content of chemical constituents of raw material. Additionally, the first-order kinetic model and the modified Gompertz model were simultaneously used to estimate the CH4 yield results of hurd. The first-order kinetic model resulted in the best fit [R-2 >= 0.96; root mean square error (RMSE) <= 0.225] with predicted yield for untreated control; while for pretreated hurds, the modified Gompertz model was the best fitting one (R-2 >= 0.98; RMSE <= 0.503).
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    Holistic biorefinery approach for biogas and hydrogen production: Integration of anaerobic digestion with hydrothermal carbonization and steam gasification
    (Academic Press Inc Elsevier Science, 2024) Daglioglu, S. Tugce; Peker, M. Eser; Duman, Gozde; Aric, Alpcan; Karagoz, Sadik Can; Ogut, Tuba Ceren; Azbar, Nuri
    Recently, the integration of biochemical and thermochemical processes is recognized as a promising strategy for the valorization of lignocellulosic biomass into renewable energy production. In this study, different routes for the valorization of hemp hurd for biohydrogen and biomethane production were proposed, including anaerobic digestion (AD), hydrothermal carbonization, and steam gasification. AD results revealed that NaOH pre-treatment of hemp hurd improved biomethane production yield by 164%. Comparing hydrochars from raw hemp, digestate derived hydrochars had higher mass yield due to changes in composition during AD as well as high ash content of digestates. It was found that high ash content of digestates originated from inorganic compounds in inoculum that accumulated over hemp hurd during anaerobic digestion process. Among feedstocks (hydrochars and raw hemp hurd), hemp hurd derived hydrochar at 200 degrees C showed the best performance in terms of H-2 yield (1278 mL/g) whereas carbon efficiency reached % 92 in case of digestate derived hydrochar at 200 degrees C. HTC improved the steam gasification performance of hemp hurd whereas hydrochars from NaOH pretreated digestate yielded lowest hydrogen production due to the high content of inorganics, particularly phosphorus (P) and aluminum (Al). According to BMP test, spent liquor obtained at the lowest HTC temperature (200 degrees C) exhibited the highest BMP, reaching 213 mL CH4/g COD. Considering the overall gas products of four different routes, it is concluded that HTC as a post-treatment exhibits slightly better performance than HTC as pre-treatment. Although alkali pretreatment enhanced the anaerobic digestion performance, the resulting hydrochars exhibited low gasification activity.