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Enhanced Methane and Hydrogen production in Reverse Membrane Bioreactors via Syngas Fermentation
University of Borås, Faculty of Textiles, Engineering and Business.ORCID iD: 0000-0002-6886-4994
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Sustainable development
According to the author(s), the content of this publication falls within the area of sustainable development.
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 [en]
syngas fermentation, CH4, H2, cell washout, inhibitors, mass transfer
National Category
Industrial Biotechnology
Research subject
Resource Recovery
Identifiers
URN: urn:nbn:se:hb:diva-21740ISBN: 978-91-88838-45-2 (print)ISBN: 978-91-88838-46-9 (electronic)OAI: oai:DiVA.org:hb-21740DiVA, id: diva2:1352281
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: 2019-11-06Bibliographically approved
List of papers
1. Rapid bio-methanation of syngas in a reverse membrane bioreactor: membrane encased microorganisms
Open this publication in new window or tab >>Rapid bio-methanation of syngas in a reverse membrane bioreactor: membrane encased microorganisms
2015 (English)In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 178, p. 334-40Article in journal (Refereed) Published
Abstract [en]

The performance of a novel reverse membrane bioreactor (RMBR) with encased microorganisms for syngas bio-methanation as well as a co-digestion process of syngas and organic substances was examined. The sachets were placed in the reactors and examined in repeated batch mode. Different temperatures and short retention time were studied. The digesting sludge encased in the PVDF membranes was able to convert syngas into methane at a retention time of 1 day and displayed a similar performance as the free cells in batch fermentation. The co-digestion of syngas and organic substances by the RMBR (the encased cells) showed a good performance without any observed negative effects. At thermophilic conditions, there was a higher conversion of pure syngas and co-digestion using the encased cells compared to at mesophilic conditions.[on SciFinder (R)]

Keywords
cell retention, co-digestion, membrane bioreactor, methane, syngas fermentation
National Category
Industrial Biotechnology
Research subject
Resource Recovery
Identifiers
urn:nbn:se:hb:diva-98 (URN)10.1016/j.biortech.2014.07.071 (DOI)000347150700044 ()2-s2.0-84920157057 (Scopus ID)2320/13980 (Local ID)2320/13980 (Archive number)2320/13980 (OAI)
Note

MEDLINE AN 2015022368(Journal; Article; (JOURNAL ARTICLE); (RESEARCH SUPPORT, NON-U.S. GOV'T))

Available from: 2015-12-06 Created: 2015-05-22 Last updated: 2019-10-25Bibliographically approved
2. Syngas Biomethanation in a Semi-Continuous Reverse Membrane Bioreactor (RMBR)
Open this publication in new window or tab >>Syngas Biomethanation in a Semi-Continuous Reverse Membrane Bioreactor (RMBR)
2016 (English)In: Fermentation, MDPI, ISSN 2311-5637, Vol. 2, no 2, article id 8Article in journal (Refereed) Published
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.

Keywords
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:nbn:se:hb:diva-9817 (URN)10.3390/fermentation2020008 (DOI)
Available from: 2016-04-28 Created: 2016-04-28 Last updated: 2019-10-25Bibliographically approved
3. Effects of Heavy Metals and pH on the Conversion of Biomass to Hydrogen via Syngas Fermentation
Open this publication in new window or tab >>Effects of Heavy Metals and pH on the Conversion of Biomass to Hydrogen via Syngas Fermentation
2018 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126Article in journal (Refereed) Published
Abstract [en]

The effects of three heavy metals on hydrogen production via syngas fermentation were investigated within a metal concentration range of 0-1.5 mg Cu/L, 0-9 mg Zn/L, 0-42 mg Mn/L, in media with initial pH of 5, 6 and 7, at 55 °C. The results showed that at lower metal concentration, pH 6 was optimum while at higher metal concentrations, pH 5 stimulated the process. More specifically, the highest hydrogen production activity recorded was 155.28% ± 12.02% at a metal concentration of 0.04 mg Cu/L, 0.25 mg Zn/L, and 1.06 mg Mn/L and an initial medium pH of 6. At higher metal concentration (0.625 mg Cu/L, 3.75 mg Zn/L, and 17.5 mg Mn/L), only pH 5 was stimulating for the cells. The results show that the addition of heavy metals, contained in gasification-derived ash, can improve the production rate and yield of fermentative hydrogen. This could lead in lower costs in gasification process and fermentative hydrogen production and less demand for syngas cleaning before syngas fermentation.

Keywords
Gasification; Syngas; Fermentative hydrogen; Heavy metals; pH
National Category
Industrial Biotechnology
Research subject
Resource Recovery
Identifiers
urn:nbn:se:hb:diva-14189 (URN)
Funder
Swedish Research Council
Available from: 2018-05-16 Created: 2018-05-16 Last updated: 2019-10-25Bibliographically approved
4. Floating membrane bioreactors with high gas hold-up for syngas-to-biomethane conversion
Open this publication in new window or tab >>Floating membrane bioreactors with high gas hold-up for syngas-to-biomethane conversion
2019 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 6Article in journal (Refereed) Published
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.

Keywords
floating MBR, syngas-to-biomethane conversion, high gas hold-up, inoculum-to-syngas ratio
National Category
Industrial Biotechnology
Research subject
Resource Recovery
Identifiers
urn:nbn:se:hb:diva-15883 (URN)10.3390/en12061046 (DOI)000464494700007 ()2-s2.0-85065448276 (Scopus ID)
Funder
Swedish Research Council
Available from: 2019-03-19 Created: 2019-03-19 Last updated: 2019-10-25Bibliographically approved

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