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Resource Recovery from Waste

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Front. Microbiol. | doi: 10.3389/fmicb.2019.00970

Upconversion of cellulosic waste into a potential 'drop in fuel' via novel catalyst generated using Desulfovibrio desulfuricans and a consortium of acidophilic sulfidogens

  • 1University of Birmingham, United Kingdom
  • 2University of Granada, Spain
  • 3University of Warwick, United Kingdom
  • 4Bangor University, United Kingdom

1. Introduction
Biogas-energy is marginally profitable against the ‘parasitic’ energy demands of processing biomass. Biogas involves microbial fermentation of feedstock hydrolyzate generated enzymatically or thermochemically. The latter also produces 5-hydroxymethyl furfural (5-HMF) which can be catalytically upgraded to 2, 5-dimethyl furan (DMF), a ‘drop in fuel’. An integrated process is proposed with side-stream upgrading into DMF to mitigate the ‘parasitic’ energy demand. 5-HMF was upgraded using bacterially-supported Pd/Ru catalysts. Purpose-growth of bacteria adds additional process costs; Pd/Ru catalysts biofabricated using the sulfate-reducing bacterium Desulfovibrio desulfuricans were compared to those generated from a waste consortium of acidophilic sulfidogens (CAS).

Methyl tetrahydrofuran (MTHF) was used as the extraction-reaction solvent to compare the use of bio-metallic Pd/Ru catalysts to upgrade 5-HMF to DMF from starch and cellulose hydrolyzates. MTHF extracted up to 65% of the 5-HMF, delivering solutions respectively containing 8.8 and 2.2 g 5-HMF/L MTHF. Commercial 5% (wt/wt) Ru-carbon catalyst upgraded 5-HMF from pure solution but it was ineffective against the hydrolyzates. Both types of bacterial catalyst (5wt%Pd/3-5wt% Ru) achieved this, bio-Pd/Ru on the CAS delivering the highest conversion yields. The yield of 5-HMF from starch-cellulose thermal treatment to 2,5 DMF was 224 and 127 g DMF/kg extracted 5-HMF respectively for CAS and D. desulfuricans catalysts, which would provide additional energy of 2.1 and 1.2 kWh/kg extracted 5-HMF.

The CAS comprised a mixed population with three patterns of metallic nanoparticle (NP) deposition. Types I and II showed cell surface-localization of the Pd/Ru while type III localized NPs throughout the cell surface and cytoplasm. No metallic patterning in the NPs was shown via elemental mapping using energy dispersive X-ray microanalysis but co-localization with sulfur was observed. Analysis of the cell surfaces of the bulk populations by X-ray photoelectron spectroscopy confirmed the higher S content of the CAS bacteria as compared to D. desulfuricans and also the presence of Pd-S as well as Ru-S compounds and hence a mixed deposit of PdS, Pd(0) and Ru in the form of various +3, +4 and +6 oxidation states. The results are discussed in the context of recently-reported controlled palladium sulfide ensembles for an improved hydrogenation catalyst.

Keywords: 5-hydroxymethylfurfural, 5-HMF upgrade, PdRu catalyst, Desulfovibrio desulfuricans, waste sulfidogenic bacteria

Received: 18 Dec 2018; Accepted: 17 Apr 2019.

Edited by:

Kirk T. Semple, Lancaster Environment Centre, Lancaster University, United Kingdom

Reviewed by:

Amy M. Grunden, North Carolina State University, United States
Eric D. Van Hullebusch, UMR7154 Institut de physique du globe de Paris (IPGP), France  

Copyright: © 2019 Mikheenko, Bolivar, Merroun, Macaskie, Sharma, Walker, Hand, Grail, Johnson and Orozco. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Lynne E. Macaskie, University of Birmingham, Birmingham, B15 2TT, United Kingdom, L.E.Macaskie@bham.ac.uk