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Syngas Biomethanation in a Semi-Continuous Reverse Membrane Bioreactor (RMBR)
University of Borås, Faculty of Textiles, Engineering and Business. (Biotechnology)
University of Borås, Faculty of Textiles, Engineering and Business. (Biotechnology)ORCID iD: 0000-0002-6886-4994
University of Borås, Faculty of Textiles, Engineering and Business. (Biotechnology)
2016 (English)In: Fermentation, MDPI, ISSN 2311-5637, Vol. 2, no 2, article id 8Article in journal (Refereed) Published
Sustainable development
The content falls within the scope of Sustainable Development
Abstract [en]

Syngas biomethanation is a potent bio-conversion route, utilizing microorganisms to assimilate intermediate gases to produce methane. However, since methanogens have a long doubling time, the reactor works best at a low dilution rate; otherwise, the cells can be washed out during the continuous fermentation process. In this study, the performance of a practical reverse membrane bioreactor (RMBR) with high cell density for rapid syngas biomethanation as well as a co-substrate of syngas and organic substances was examined in a long-term fermentation process of 154 days and compared with the reactors of the free cells (FCBR). The RMBR reached maximum capacities of H2, CO, and CO2 conversion of 7.0, 15.2, and 4.0 mmol/Lreactor.day, respectively, at the organic loading rate of 3.40 gCOD/L.day. The highest methane production rate from the RMBR was 186.0 mL/Lreactor.day on the 147th day, compared to the highest rate in the FCBR, 106.3 mL/Lreactor.day, on the 58th day. The RMBR had the ability to maintain a high methanation capacity by retaining the microbial cells, which were at a high risk for cell wash out. Consequently, the system was able to convert more syngas simultaneously with the organic compounds into methane compared to the FCBR.

Place, publisher, year, edition, pages
2016. Vol. 2, no 2, article id 8
Keywords [en]
syngas fermentation; methane production; semi-continuous process; reverse membrane bioreactor; co-substrate; cell retention
National Category
Engineering and Technology
Research subject
Resource Recovery
Identifiers
URN: urn:nbn:se:hb:diva-9817DOI: 10.3390/fermentation2020008OAI: oai:DiVA.org:hb-9817DiVA, id: diva2:924187
Available from: 2016-04-28 Created: 2016-04-28 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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Publisher's full texthttp://www.mdpi.com/2311-5637/2/2/8

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Youngsukkasem, SupansaChandolias, KonstantinosTaherzadeh, Mohammad

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