Production of Bio-alkanes from Biomass and CO2

Electro-fermentation (EF) and microbial CO2 electrosynthesis (MES) are emerging interdisciplinary technologies that can produce renewable carboxylic acids.A newly discovered photo-decarboxylase offers an innovative route for bio-alkane production from acids.The cascading photo/bio/electrochemical system advanced bio-alkanes (CnH2n+2, n = 2 to 5) biomass CO2.Systems will require optimisation reduce economic cost carbon footprint. Bioelectrochemical such as electro-fermentation fuels chemicals (such acids). The benefits of electrically driven bioprocesses include improved rate, selectivity, conversion efficiency. However, the accumulation products lead inhibition biocatalysts, necessitating further effort in separating products. recent discovery a new photoenzyme, capable converting acids bio-alkanes, has offered opportunity integration, providing promising approach simultaneous product separation valorisation. Combining strengths catalysis, we discuss circular converts value-added whilst achieving circularity. transition climate neutral future requires pathways net-zero emission energy systems. Energy sectors light-duty transportation, heating, electricity may be straightforward decarbonise via wind, wave, solar), they have witnessed significant development associated reduction past decade. elements transportation sector aviation, long-distance haulage, shipping not ideally suited electrification [1.Davis S.J. et al.Net-zero emissions systems.Science. 2018; 360eaas9793Crossref PubMed Scopus (479) Google Scholar, 2.Jenkins J.D. al.Getting zero electric power sector.Joule. 2: 2498-2510Abstract Full Text PDF (55) 3.McGinnis R. CO2-to-fuels gasoline jet fuel soon price competitive with fossil fuels.Joule. 2020; 4: 509-511Abstract (5) Scholar]. European Union proposed greenhouse gas by at least 40% below 1990 levels 2030 [4.European Commission Proposal Directive Parliament Council on Promotion Use Renewable Sources (recast). Commission, 2018Google To meet this challenging target, biofuels (see Glossary), including biomethane longer C2+ alkanes feedstocks, serve high-quality sustainable these difficult sectors. Anaerobic digestion is established biotechnology C1 methane wide range organic wastes [5.Angelidaki I. al.Biogas upgrading utilization: current status perspectives.Biotechnol. Adv. 36: 452-466Crossref (478) Scholar,6.Fu S. al.In situ biogas CO2-to-CH4 bioconversion.Trends Biotechnol. 2021; 39: 336-347Abstract (26) Scholar]; however, lower density value compared other chain alkanes. For example, pentane (C5) presents higher heating (3507 kJ/mol) than (889 (https://webbook.nist.gov/chemistry/). As such, producing more attractive considering their use drop-in fuels. Nonetheless, high-efficiency microorganisms technically typically metabolic engineering natural [7.Choi Y.J. Lee S.Y. Microbial short-chain alkanes.Nature. 2013; 502: 571-574Crossref (298) Emerging bio-based (EF), (MES), photo-biocatalysis whole cell or enzymatic level provide platform production. These used either alone combined desired products, hydrogen, alkanes, alcohols, acids. EF convert feedstock into CO2, short (SCCAs, C1–C5; acetic/butyric acid) [8.Schievano A. al.Electro-fermentation–merging electrochemistry fermentation industrial applications.Trends 2016; 34: 866-878Abstract (139) SCCAs together upgraded medium (MCCAs, C6–C12, caproic through MES, surplus [9.Prévoteau al.Microbial CO2: forever promise?.Curr. 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By introducing polarised electrodes, imposing electrical field environment, thereby influencing metabolism provides hybrid external electrons exchanged solid act alternative oxidising/reducing equivalents [16.Moscoviz al.Electro-fermentation: how drive using electrochemical systems.Trends 856-865Abstract (146) Depending electrodes electron sinks donors, configuration categorised cathodic anodic EF, respectively (Box 1). conditions electrochemically controlled optimise redox condition, favour growth, regulate metabolism, promote extracellular transfer leads yield selectivity methane, alcohols (ethanol, butanol), (acetic acid, butyric acid). only biomethane, but also versatile precursors even higher-valued chemical [17.Jiang Y. al.Electrochemical control potential arrests methanogenesis regulates mixed culture electro-fermentation.ACS Sustain. Eng. 6: 8650-8658Crossref (37) Scholar], MCCA, polyhydroxyalkanoates, single proteins, multicarbon (for heavy goods vehicles).Box 1Electro-Fermentation versus Traditional FermentationWhat Is Anodic Cathodic EF?The presence flexible consume supply I). In working electrode acts anode dissipate excess during fermentation; final oxidised substrate example ethanol glycerol). contrast, supplies reduced acetic acid glucose). main source nor targeted product, stimulator allowing take place unbalanced enhanced rate.What Are Advantages over Fermentation?The stability dependent many process oxidation–reduction potential, media buffering capacity, accumulation), leading constrained feasibility environmental sustainability. optimised storage fuels/chemicals, affecting condition (NADH/NAD+ balance), facilitate anodic/cathodic reactions consuming/supplying electrons, achieve simply varying potential. What EF? rate. Fermentation? Table 1 summarises various applications. regulating different potentials ?1.0, ?0.6, ?0.2 V (versus Ag/AgCl), (SCCA, C2–C4) obtained glucose External stimulation catalysts enhance SCCA C2 food waste; accompanied enrichment acidogenic bacteria [18.Shanthi Sravan al.Electrofermentation waste – acidogenesis towards volatile production.Chem. 334: 1709-1718Crossref Production MCCA C6 donors lactic initiate elongation reaction reverse ?-oxidation pathway; (2C2H5OH + CH3COO– C5H11COO– 2H2O, ?G0 –79.0 kJ/mol). Despite progress technology, production, investigation needs performed understand role important variables, applied activities regulatory enzymes, functional communities. quantify efficiency Moscoviz colleagues introduced indicator ‘EF coefficient’, calculated ratio charge transferred circuit total achieved coefficient varies between 0.01 0.38 pure strains cultures effectiveness affected conditions, both dissolved mediators interactions surface typical syntrophy, occurs close thermodynamic equilibrium, minor disturbance substrates/products concentration shift pathway. Recent research found direct interspecies conductive materials graphene [19.Lin al.Graphene facilitates protein-derived glycine anaerobic digestion.iScience. 10: 158-170Abstract Scholar,20.Lin al.Boosting rate graphene: digestion.Bioresour. 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This suggests advance electroactive enriched, [24.Feng Q. al.Bioelectrochemical upflow reactor effluent recirculation acidic distillery wastewater.Bioresour. 241: 171-180Crossref (32) Scholar].Table 1Production Various Carboxylic Acids Electro-Fermentation ApplicationsSubstrateMain productionWorking (V SHEaSHE, standard electrode.)Temperature (°C)Microbial cultureEF performance fermentationRefsGlycerolAcetic acid0.237Engineered Escherichia coliIncreased glycerol consumption (anodic EF)[55.Sturm-Richter K. al.Unbalanced coli heterologous transport interaction cells.Bioresour. 186: 89-96Crossref (68) Scholar]GlucoseAcetic/propionic/ acid0/–0.4/–0.8bCalculated based Ag/AgCl (saturated KCl) reference against SHE +0.2 V.35Mixed cultureTuneable (cathodic EF)[17.Jiang Scholar]Food wasteAcetic/propionic/ acid–0.6 (reference indicated)28Mixed cultureTotal increased 72.3% EF)[18.Shanthi Scholar]SucroseButyric acid–0.2bCalculated V.37Clostridiumtyrobutyricum35% increase EF)[56.Choi O. al.Butyrate Clostridium tyrobutyricum donor.Biotechnol. Bioeng. 2012; 109: 2494-2502Crossref (99) Scholar]Glucose, acetate, ethanolIso-butyric acid–0.725Mixed cultureAlmost 20-fold iso-butyrate (compared open controls) EF)[57.Villano M. al.Electrochemically substrates undefined cultures.ChemSusChem. 3091-3097Crossref (23) Scholar]Acetate, ethanolCaproic aid–0.9bCalculated V.30Mixed cultureCaproate 28% EF)[58.Jiang al.Electro-fermentation fresh acclimated cathode.Energy Convers. Manag. 204112285Crossref (17) Scholar]a SHE, electrode.b Calculated V. Open table tab Since built ‘classical’ shown yields, its technological maturity defined technology readiness (TRL) regarded somewhere basic (TRL 3–4). Improving TRL reveal microorganisms, developing strategies improve selectivity. A detailed techno-economic assessment would needed scale-up implementation process. Both MES mechanisms affect differences following: nonspontaneous without driving force; cathode conducting reducing acid), while cathode; (0.001–10 A/m2) (0.01–200 (which uses solely power) [25.Jiang al.Carbon dioxide valorization electro-fermentation.Water Res. 2019; 149: 42-55Crossref (108) (Table Box 2). Acetic mainly produced; (iso)butyric/caproic relatively low concentrations. highest acetate 1330 g/m2 electrode/day design optimal operational [26.Jourdin L. al.Bringing high-rate, CO2-based closer practical operating conditions.Environ. Sci. 50: 1982-1989Crossref (97) comparison, rates n-butyrate (nC4) n-caproate (nC6) were 160 46 electrode/day, respectively, felt [27.Jourdin al.Critical biofilm growth throughout unmodified felts allows continuous up caproate density.Front. 7Crossref (78) several factors, material/architecture, density, inoculum, all fundamental [28.Zhen G. electrolysis biorefinery clean electrofuels generation: situation, challenges perspectives.Prog. Combust. 63: 119-145Crossref (88) C4–6 (typically internally intermediate) Electron modulation theory one mole 32 (6HCO3?+37H++32e??CH3CH24COO?+16H2O), eight (2HCO3?+9H++8e??C2H3O2?+4H2O). formation restricted kinetic challenge proton coupled reactions, inherently large potentials.Table 2Production (C2+) ElectrosynthesisCathode materialCathode cultureMain (g/l)RefsGas diffusion biocathode?1.1 ?1.330Enriched sludgeButyric 0.1[32.Bajracharya al.Application biocathode dioxide.Environ. Pollut. 23: 22292-22308Crossref (105) Scholar]Carbon felt?0.8532Enriched cultureButyric 2.85 Caproic 1.05[27.Jourdin felt?1.0232Enriched 9.3 3.1[48.Jourdin al.Enhanced above steering loading hydraulic retention time.Bioresour. Reports. 7100284Crossref (38) Scholar]MXene-coated felt?0.635Mixed culturePropionic 1.57 Butyric 0.87[59.Tahir al.A novel MXene-coated performance.Chem. 381122687Crossref Scholar]Graphite granules?0.835Mixed 3.1 Iso-butyric 1.6 1.2[60.Vassilev isobutyric, butyric, acids, corresponding dioxide.ACS 8485-8493Crossref (91) electrode. 2Microbial Electrosynthesis Producing AcidsModified Cathode StructureThe interface plays key formation. properties biocompatibility, area, investigated develop effective configuration. methods developed modification cathodes Figure I 3D porous structure group attachment improving positively charged microorganism adsorption, deliver cathode–microorganism activity.Electron Transfer MechanismThe indirect (IET) mediator (DET) cytochromes nanowires IET diffusible carriers microorganisms; gradient rate-limiting parameter Fick’s law. DET physical contact outer membrane c-type cytochromes, nanowire, biocompatible materials; underlying molecular accept clear [61.ter Heijne al.Electron biofilms.Trends 34-42Abstract (16) Scholar,62.Logan B.E. al.Electroactive systems.Nat. Microbiol. 17: 307-319Crossref (341) Scholar].Metabolic Pathways Acid ProductionThe dominant compound (C2H4O2) since first proof-of-concept [63.Nevin K.P. electrosynthesis: feeding water compounds.MBio. 2010; 1e00103-10Crossref (581) Recently, (C4H8O2) (C6H12O2) respective possible, [30.Bian challenges, perspectives context bioeconomy.Bioresour. 302122863Crossref (71) shows possible depends predominant microbes, hierarchy. originates acetyl-CoA, precursor intermediates (C2), propionic (C3), (C3). Subsequent (C4) occur moles CO2. (C6) (or CO2). Direct elon