Microbial | electrochemical CO2 reduction: To integrate or not to integrate?

Paniz Izadi is a lead scientist for the H2020-funded project VIVALDI at Helmholtz-Centre Environmental Research (UFZ), Germany. Her current research focuses on developing methods electrochemical CO2 reduction and its interfacing to microbiology industrial applications, following her previous microbial in bio-electrochemical systems. She received PhD chemical engineering from Newcastle University, UK 2020.Falk Harnisch holds full professorship Leipzig University electrobiotechnology group leader He his Greifswald Germany 2009, as well several fellowships awards, currently serving president of International Society Microbial Electrochemistry Technology. His ranges fundamentals electrochemistry via electro-organic synthesis technologies. 2020. Falk Carbon dioxide (CO2) must turn waste feedstock order establish circular economy. Although there consensus that chemicals fuels consumer goods will be based carbon was recently CO2, one can only make inferences regarding technology platform(s) needed reach such an transformation. Certainly, petro-based industries not simply replaced by technology. Rather, broad portfolio platforms comprised physical, biological technologies expected allow development toward true circularity (bio)chemical synthesis. Among these are interweaving synthesis.1Harnisch F. Urban C. Electrobiorefineries: unlocking synergy conversions.Angew. Chem. Int. Edition. 2018; 57: 10016-10023https://doi.org/10.1002/anie.201711727Crossref PubMed Scopus (43) Google Scholar immediate utilization gas fermentation, instance, suffers low solubility gaseous compounds their liquid phase. It limits accessibility and/or H2 cells therefore conversion efficiency.2Vees C.A. Neuendorf C.S. Pflügl S. Towards continuous bioprocessing with solventogenic acetogenic clostridia: challenges, progress perspectives.J. Ind. Microbiol. Biotechnol. Official J. Soc. 2020; 47: 753-787https://doi.org/10.1007/s10295-020-02296-2Crossref (21) allows use electric energy exploit synthesis; however, CO2-reduction reaction (CO2RR) characterized product commonly limited C1 or C2 compounds3Nitopi Bertheussen E. Scott S.B. Liu X. Engstfeld A.K. Horch Seger B. Stephens I.E.L. Chan K. Hahn et al.Progress perspectives copper aqueous electrolyte.Chem. Rev. 2019; 119: 7610-7672https://doi.org/10.1021/acs.chemrev.8b00705Crossref (1218) but possesses high kinetics, particularly when compared reduction.4Hegner R. Rosa L.F. Electrochemical formate indium electrodes efficiency selectivity pH neutral electrolytes.Appl. Catal. B: Environ. 238: 546-556https://doi.org/10.1016/j.apcatb.2018.07.030Crossref (56) Therefore, combining integrating conversions CO2RR seems very appealing. Integration may harnessing best both systems utilizing create products. (MES) transformations purposeful transformation into desired product.1Harnisch MES activity autotrophic microorganisms reduce using cathodic electrons hydrogen. Despite initial excitement this process significant has stagnated face insurmountable hurdles. The main obstacles electron transfer rates hence rates, portfolio, insufficient yields, long amount time required electrocatalyst production start-up time.5Prévoteau A. Carvajal-Arroyo J.M. Ganigué Rabaey electrosynthesis CO2: forever promise?.Curr. Opin. 62: 48-57https://doi.org/10.1016/j.copbio.2019.08.014Crossref (124) Synthesis also less reactions. Through CO2RR, first electrochemically reduced yield (HCOOH) other compounds, which already established feedstocks syntheses. foresee addition formatotrophs (formate-consuming microorganisms) synthesis, strain excellent hosts, including yeasts.6Cotton Claassens N.J. Benito-Vaquerizo Bar-Even Renewable methanol feedstocks.Curr. 168-180https://doi.org/10.1016/j.copbio.2019.10.002Crossref (98) yields reported Li al.7Li H. Opgenorth P.H. Wernick D.G. Rogers Wu T.-Y. Higashide W. Malati P. Huo Y.-X. Cho K.M. Liao J.C. Integrated electromicrobial higher alcohols.Science. 2012; 335: 1596https://doi.org/10.1126/science.1217643Crossref (465) Since then, taken place concerns components, engineering. When different approaches feasible. integration occur situ, is, compartment (Figure 1A ). converted proceeding cathode linked microorganisms. Here, synchronization challenge. To avoid disturbing electrode, form no biofilm thereon favorable. submersed more appealing terms volumetric especially exploiting co-cultures microorganisms, creation food webs gaining complex noteworthy often side H2, ideal source many catalysts. Alternatively, yielding occurs while being separated spatially (Figures 1B 1C). solution composition critical, it needs balance requirements steps thus provide (optimal) conditions A challenge inhibition bio-products. Using two separate reactors 1B), inline separation products reusing overcome problem. Solution design challenging some vital growth hamper CO2RR.4Hegner In line, purity feed relevance—for assuming flue contains impurities (e.g. traces O2 sulfur compounds). As biomass detrimental present electrode affected reaction. Thus, removal, e.g., filtering, advantageous reactors. addition, small share (e.g., O2) tolerated CO2RR. We confident us operational required; controlling integrated processes remains challenging. reactions fully This decoupling space time. independent, they do affect each other, solutions optimized respective step. Further, separating them concentration amendment—for trace elements—of containing before supplying bioreactor. rate disconnected 1C), whereas requires extent operating 1A). At glance, even allowing precise control feeding advantageous, toxic, latter removed downstream processing (DSP). toxicity threshold (ranging <100 mM weak dehydrogenases [e.g. E.coli] >100 those strong yeasts] dehydrogenases), than causes decline biosynthesis.6Cotton However, locally gradients bioreactor limit improved mass transfer, increased energy-consuming agitation implementation baffles.8Liew Martin M.E. Tappel R.C. Heijstra B.D. Mihalcea Köpke M. Gas fermentation—a flexible platform commercial scale low-carbon-fuels renewable feedstocks.Front. 2016; 7: 694https://doi.org/10.3389/fmicb.2016.00694Crossref (229) argue limitation elegantly economically appropriate reactor situ integration, three-dimensional discussed below. above illustrated become competitive, assets fact kinetics ratio active surface area volume diversity competitor fermentation syngas (from CO/H2O CO2/H2). 28 mg L?1 CO, 1.6 1.7 g CO2; 293K; 1atm8Liew Scholar) sets boundaries bio-production, large scale. we clear advantage 1A) case used. electrodes, diffusion (GDEs) seem most promising us, due role enhancing media ability decrease internal resistance removing bubbles covering areas directly media.9Song J.T. Song Kim Oh conversion: liquid-phase gas-phase systems.Catalysts. 9: 224https://doi.org/10.3390/catal9030224Crossref (58) GDEs, transported through layer 2),9Song permanent availability sites. over assures energetic bioconversion H2/CO2 80%–90% 60%–80% anaerobic acetogens).10Claassens Cotton C.A.R. Kopljar D. Making quantitative sense production.Nat. 2: 437-447https://doi.org/10.1038/s41929-019-0272-0Crossref (79) formate, achieved. Methanol rich been known syntheses.10Claassens strongly depends materials.11Li Zhang Xiang Rasul Fontmorin J.-M. Roldan Taylor Feng Y. Banerji L. al.How go beyond CO2.Sustainable Energy Fuels. 2021; 5: 5893-5914https://doi.org/10.1039/D1SE00861GCrossref For (In) tin (Sn) (also Hg, Cd, etc.) catalyzing oxidation state (Cu2O) metals Cu3Pt Cu3Pd) (although potentials). There number external costs need considered bio-based economy lab bench reality. Product recovery DSP, extraction, any presented turning power fuels. special importance designs recirculation, potentially toxic effect bio-products 1B). microbially produced carboxylic acids have damaging effects cell membrane resulting inhibition. Production longer chain terpenes, drugs, proteins increases economic value makes convenient. quality important Even percentage oxygen cement industry, includes oxides nitrogen dioxides dust oxygen,12Vatopoulos Tzimas Assessment capture manufacturing process.J. Clean. Prod. 32: 251-261https://doi.org/10.1016/j.jclepro.2012.03.013Crossref (99) could disturb overall efficiency. case, extra purification leading increase costs. compression three were calculated require energy.12Vatopoulos today, ethanol butanol potential alternatives fossil-based transportation Syngas developed pursued companies LanzaTech joint partner Shougang (Chinese Steel company), Genomatica, Kiverdi, IneosBio, Coskata,13Liew F.E. Nogle Abdalla T. Rasor B.J. Canter Jensen R.O. Wang Strutz Chirania De Tissera al.Carbon-negative acetone isopropanol pilot scale.Nat. 2022; 40: 335-344https://doi.org/10.1038/s41587-021-01195-wCrossref Scholar,14Sun Atiyeh H.K. Huhnke R.L. Tanner R.S. biofuels chemicals: review.Bioresour. Technol. Rep. 100279https://doi.org/10.1016/j.biteb.2019.100279Crossref (76) particular IneosBio Coskata stopped operation financial difficulties14Sun Scholar). operationally feasible remarkable efforts taken, achievements past years. Different multi-stage gas-liquid enhanced patented.14Sun COVID-19 pandemic decreased 2020, biorefineries remaining major drivers clean US, Brazil, certain parts Asia Europe.15RFA Ethanol Industry Outlook. Fuels Association, 2022https://ethanolrfa.org/file/2145/RFA%202022%20Outlook.pdfGoogle pandemic, 2.7 million tons captured 2021 biorefineries, used further applications bottling processing. acetate, isoprene 3-hydroxypropionate, genetically modified growing observed syntheses, organic syntheses scales mature. Thus far, valuable adiponitrile (a key intermediate nylon-6,6) decades scales, instance Japan (Asahi Chemical Nobeoka).16Botte G.G. industry.Electrochem. Interf. 2014; 23: 49-55https://doi.org/10.1149/2.f04143ifCrossref (0) advantages simple energies biosynthesis ambient temperature pressure operation, steps, few polluting application industry (especially without scale) seen consequence up until now. These include missing suitable resources technologies; considerable excessive capital expenditures, implementing changes existing lines; lack scientists engineers educated electrochemistry; collaboration between governmental sectors. benefit routes diverse, value-added, energies, partnerships universities institutes, government, required. run society shareholders. authors acknowledge support funding European Union’s Horizon 2020 innovation program under grant agreement 101000441 . work supported Helmholtz Association frame Platform "Tapping nature’s sustainable healthy environment" UFZ idea article manuscript conceived written P.I. F.H. declare competing interests.