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Floating membrane bioreactors with high gas hold-up for syngas-to-biomethane conversion
University of Borås, Faculty of Textiles, Engineering and Business. (Biotechnology)ORCID iD: 0000-0002-6886-4994
Department of Environmental Engineering, Istanbul Technical University. (Biotechnology)
University of Borås, Faculty of Textiles, Engineering and Business. (Biotechnology)ORCID iD: 0000-0003-4887-2433
2019 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 6Article in journal (Refereed) Published
Sustainable development
According to the author(s), the content of this publication falls within the area of sustainable development.
Abstract [en]

The low gas-to-liquid mass transfer rate is one of the main challenges in syngas biomethanation. In this work, a new concept of the floating membrane system with high gas hold-up was introduced in order to enhance the mass transfer rate of the process. In addition, the effect of the inoculum-to-syngas ratio was investigated. The experiments were conducted at 55 °C with an anaerobic mixed culture in both batch and continuous modes. According to the results from the continuous experiments, the H2 and CO conversion rates in the floating membrane bioreactor were approximately 38% and 28% higher in comparison to the free (suspended) cell bioreactors. The doubling of the thickness of the membrane bed resulted in an increase of the conversion rates of H2 and CO by approximately 6% and 12%, respectively. The highest H2 and CO consumption rates and CH4 production rate recorded were approximately 22 mmol/(L·d), 50 mmol/(L·d), and 34.41 mmol/(L·d), respectively, obtained at the highest inoculum-to-syngas ratio of 0.2 g/mL. To conclude, the use of the floating membrane system enhanced the syngas biomethanation rates, while a thicker membrane bed resulted in even higher syngas conversion rates. Moreover, the increase of the inoculum-to-syngas ratio of up to 0.2 g/mL favored the syngas conversion.

Place, publisher, year, edition, pages
2019. Vol. 12, no 6
Keywords [en]
floating MBR, syngas-to-biomethane conversion, high gas hold-up, inoculum-to-syngas ratio
National Category
Industrial Biotechnology
Research subject
Resource Recovery
Identifiers
URN: urn:nbn:se:hb:diva-15883DOI: 10.3390/en12061046ISI: 000464494700007Scopus ID: 2-s2.0-85065448276OAI: oai:DiVA.org:hb-15883DiVA, id: diva2:1297125
Funder
Swedish Research CouncilAvailable from: 2019-03-19 Created: 2019-03-19 Last updated: 2019-10-25Bibliographically approved
In thesis
1. Enhanced Methane and Hydrogen production in Reverse Membrane Bioreactors via Syngas Fermentation
Open this publication in new window or tab >>Enhanced Methane and Hydrogen production in Reverse Membrane Bioreactors via Syngas Fermentation
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

of waste treatment processes, such as the anaerobic digestion. This biochemical process converts organic substrates into biogas, with anaerobic microorganisms. However, some types of substrates have low bio-degradability due to its recalcitrance or the presence of inhibitors. This can be solved by the coupling of anaerobic digestion with gasification, a thermochemical process that can convert organic substrates into syngas (H2, CO, and CO2) regardless of the substrate´s degradability. Consequently, syngas can be converted into biogas and other fermentative products via anaerobic digestion, in a process known as syngas fermentation. In comparison to the catalytic conversion of syngas, syngas fermentation has several advantages such as lower sensitivity to CO/H2/CO2 ratio and to syngas contaminants as well as higher product specificity.

The main goal of this thesis was to improve the syngas conversion rate into CH4 and H2 by addressing the cell washout, the cell inhibition by syngas contaminants, and the low gas-to-liquid mass transfer, which are major challenges in syngas fermentation. For this purpose, a reverse membrane bioreactor, containing a mixed culture encased in membranes, was used in various set ups. The membranes were used in order to retain the cells inside the bioreactors, to protect the cells against inhibitors, and to improve the gas holdup and gas-to-cell contact by decreasing the rise velocity of syngas bubbles. As evident from the results, the cell washout was successfully tackled during a continuous experiment that lasted 154 days. In addition, membrane bioreactors fed with the syngas contaminants, toluene and naphthalene, achieved approximately 92% and 15% higher CH4 production rate, respectively, compared with the free cell bioreactors. In order to improve the gas holdup and consequently the gas-to-liquid mass transfer of syngas, a floating membrane bed bioreactor was set up. This bioreactor contained membrane sachets, filled with inoculum that formed a packed floating membrane bed and achieved an increase of 38% and 28% for the conversion rate of H2 and CO, respectively. Furthermore, the addition of a mixture of heavy metals improved the production rates and yields during the syngas conversion into fermentative H2.

Place, publisher, year, edition, pages
Borås: Högskolan i Borås, 2019
Series
Skrifter från Högskolan i Borås, ISSN 0280-381X ; 99
Keywords
syngas fermentation, CH4, H2, cell washout, inhibitors, mass transfer
National Category
Industrial Biotechnology
Research subject
Resource Recovery
Identifiers
urn:nbn:se:hb:diva-21740 (URN)978-91-88838-45-2 (ISBN)978-91-88838-46-9 (ISBN)
Public defence
2019-11-29, D207, University of Borås, Allégatan 1, Borås, 10:00 (English)
Opponent
Available from: 2019-11-06 Created: 2019-09-18 Last updated: 2019-11-21Bibliographically approved

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Chandolias, KonstantinosTaherzadeh, Mohammad J

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