# Power-to-X with biological step Microbial electrosynthesis and power-to-methane: renewable electricity and CO2 fed to electroactive microbes at a cathode that fix CO2 via the Wood-Ljungdahl pathway into acetate, alcohols, biomethane and single-cell protein. Source: https://en.bioecon.ru/technology/power-to-x-with-biological-step-microbial-electrosynthesis/ Updated: 2026-08-18 ## Overview and value chain Markers: [EC: REACH / Renewable Energy Directive III | OECD: bioenergy | Regulator: EPA (USA), REACH (EU), NEA (China)] Power-to-X with a biological step uses renewable electricity to drive living microbes that reduce CO2 into fuels, chemicals and protein. The flagship mode, microbial electrosynthesis (MES), runs at a cathode immersed in an anaerobic broth of electroactive acetogens such as *Sporomusa ovata* or *Clostridium ljungdahlii*: electrons travel from the electrode into the cell — directly through outer-membrane cytochromes and conductive nanowires, or indirectly via electrolytically generated hydrogen — and the microbe uses them, together with CO2, to build acetyl-CoA through the Wood-Ljungdahl pathway. From that central intermediate it releases acetate, ethanol or butanol, or grows as single-cell protein. A closely related mode, power-to-methane, uses hydrogenotrophic archaea such as *Methanothermobacter* to convert CO2 and green hydrogen into grid-quality biomethane. Unlike abiotic Power-to-Gas (water electrolysis plus a high-temperature Sabatier reactor), the biological route runs at ambient pressure and around 30-37C, which is its main engineering appeal and its main scale-up hurdle. The key directions of power-to-X with a biological step are: 1. **Microbial electrosynthesis to acetate and chemicals (MES to Acetate & Chemicals):** electroactive acetogens at a cathode fix CO2 into C2-C6 building blocks (acetate, ethanol, butanol) for the green-chemistry and polymer industries. 2. **Power-to-methane / biological methanation (Power-to-Methane):** hydrogenotrophic archaea convert CO2 and green hydrogen into pipeline-quality biomethane for gas-grid injection. 3. **CO2-to-protein (CO2-to-Protein):** hydrogen-oxidizing microbes turn electricity-derived hydrogen and CO2 into single-cell protein for feed and food. 4. **Electrode and biofilm engineering (Electrode & Biofilm Engineering):** high-surface-area 3D porous cathodes and conductive biofilms raise the electron-transfer rate that ultimately sets reactor productivity. ### Sectoral value chain ``` [renewable power + CO2] ──> [MES bioelectrochemical reactor] ──> [cathode electron transfer to microbes] │ (Wood-Ljungdahl CO2 fixation) │ [target product: acetate / methane / protein] <─── [membrane separation] <─── [metabolite-rich broth] ``` ### Value chain levels | Level | Description | Key inputs/outputs | |:---|:---|:---| | **Renewable Power & CO2** | supply of curtailed renewable electricity and captured CO2 from flue gas or direct air capture. | **In:** wind/solar power, point-source CO2. **Out:** DC current, compressed CO2. | | **Biocatalyst & Biofilm** | cultivation of electroactive acetogens or archaea and formation of a conductive cathode biofilm. | **In:** pure cultures, anaerobic media. **Out:** colonized high-area cathodes. | | **MES Reactor** | bioelectrochemical reduction of CO2 in sealed reactors under controlled potential and pH. | **In:** electricity, CO2, biocathodes, IrO2 anodes. **Out:** organic-acid/alcohol broth or biomethane. | | **Separation & Downstream** | concentration of products from the broth by membrane ultrafiltration and distillation. | **In:** reactor broth, TFF membranes. **Out:** glacial acetic acid, ethanol, clean water. | | **Product Upgrade** | chemical or second-stage biological upgrade of acetate into lipids, bioplastics or protein. | **In:** acetate, oleaginous yeasts. **Out:** bio-based oils, PHA, single-cell protein. | | **Quality & MRV** | purity verification, coulombic-efficiency accounting and carbon-footprint certification. | **In:** GC-MS, coulombic logs, LIMS. **Out:** certified green chemistry with a negative-CO2 footprint. | Cross-cutting technologies of the sector: - **Cathode-to-microbe electron transfer (Electron Transfer Interface):** direct transfer via cytochromes and conductive pili, plus H2-mediated transfer via hydrogenases, together set the coulombic efficiency of the cell. - **Wood-Ljungdahl pathway (Wood-Ljungdahl Pathway):** the most energy-efficient biological CO2-fixation route, converting two CO2 molecules into one acetyl-CoA that branches into acetate, alcohols and biomass. - **Pressurized gas dissolution (Hollow-Fiber Membrane Biofilm Reactors):** hollow-fiber membranes deliver CO2 and hydrogen bubble-free straight into the biofilm, lifting gas availability into the cells. --- ## US The US funds microbial electrosynthesis through the Department of Energy and the national labs, while a cluster of startups pushes CO2-to-chemicals and CO2-to-protein routes toward commercial scale. ### DOE and NREL R&D, CO2-to-chemicals startups, gas-fermentation anchor - **DOE Office of Science and NREL:** federal grants fund the electrode-cell interface and acetogen metabolic engineering; NREL develops scalable bioelectrochemical reactors with high-area cathodes. - **Cemvita Factory:** uses engineered Wood-Ljungdahl microbes to make bio-ethylene, glycols and other olefins straight from CO2 and electricity, targeting electrofuels and bio-based plastics. - **NovoNutrients:** runs hydrogen-driven gas fermentation to turn CO2 and electricity-derived hydrogen into single-cell-protein ingredients for aquafeed and food. - **LanzaTech (commercial anchor):** although gas-fermentation rather than electrosynthesis proper, its commercial CO/CO2-to-ethanol plants are the reference deployment that MES routes aim to displace on cost. --- ## CN China couples surplus wind and solar in its western provinces to bioelectrochemical and biomethanation pilots, backed by CAS institutes and the National Energy Administration's decarbonization mandate. ### CAS Shenzhen MES R&D, western-province power-to-gas, industrial-biotech scale-up - **CAS Shenzhen Institute of Advanced Technology:** a leading Chinese MES R&D center, engineering conductive-polymer biofilms and carbon-nanotube composite cathodes to raise coulombic efficiency. - **Western-province integration:** curtailed wind and solar in Xinjiang and Gansu power bioelectrochemical reactors that convert CO2 from coal-plant flue gas into stable biomethane for the West-East gas pipeline. - **Dalian Institute of Industrial Biotechnology (CAS):** scales one-carbon gas-fermentation and bioelectrochemical processes from bench to industrial demonstration, anchoring the Chinese industrial-biotech pipeline. --- ## EU The EU leads on commercial biological methanation and funds multi-center MES consortia under Horizon Europe, framed by REACH and the Renewable Energy Directive. ### Electrochaea commercial biomethanation, Horizon Europe Power-to-X, academic MES hubs - **Electrochaea:** operates commercial-scale biological methanation plants in Denmark and Switzerland; its patented thermophilic *Methanothermobacter* catalyst converts CO2 and green hydrogen into pipeline-quality biomethane at high selectivity. - **Horizon Europe Power-to-X programs:** targeted funding integrates Power-to-X with wastewater and biogas plants, using their CO2 streams as feedstock. - **Academic MES hubs:** the University of Girona and Ghent University advance MES reactor design — 3D porous carbon cathodes and biofilm engineering — for specialty acids from industrial emissions. --- ## Leading companies and research institutes | Company / Institute | Country | Key products / platforms | Tech features | Status 2026 | |:---|:---|:---|:---|:---| | **Electrochaea** | 🇩🇪 Germany | *BioCat biomethanation* | thermophilic archaea (*Methanothermobacter*) convert CO2+H2 to pipeline-grade methane | commercial | | **LanzaTech** | 🇺🇸 USA | *Gas fermentation* | commercial microbial fermentation of CO/CO2 off-gas to ethanol and chemicals | commercial | | **NovoNutrients** | 🇺🇸 USA | *CO2-to-protein* | hydrogen-driven acetogenesis to single-cell-protein ingredients | pilot (acquired by Biosphere, 2026) | | **Cemvita Factory** | 🇺🇸 USA | *Bio-ethylene / electrofuels* | engineered Wood-Ljungdahl microbes making olefins from CO2 and electricity | pilot | | **Dalian IIB** | 🇨🇳 China | *Industrial-biotech R&D* | one-carbon gas-fermentation and bioelectrochemical process scale-up | research | | **University of Girona** | 🇪🇸 Spain | *MES reactor R&D* | 3D porous carbon cathodes and biofilm engineering for acetate production | research | --- ## Tech stack and innovations The stack sits at the intersection of electrocatalysis, strict-anaerobe physiology and high-pressure gas mass transfer. 1. **Cathode-to-microbe electron transfer (Electron Transfer Interface):** - direct transfer: bacteria dock on the cathode through c-type cytochromes and conductive nanowires; 3D porous carbon-felt cathodes, often loaded with nickel or magnetite nanoparticles, enlarge the contact area. - H2-mediated transfer: the cathode electrolyzes water to hydrogen at mild overpotential (molybdenum-disulfide or low-platinum coatings), and bacterial hydrogenases split the hydrogen to feed reduction. 2. **Wood-Ljungdahl pathway biochemistry (Wood-Ljungdahl Pathway):** - the most energy-efficient CO2-fixation route: a methyl branch reduces one CO2 to a methyl group (via formate and tetrahydrofolate) while a carbonyl branch reduces a second CO2 to CO (via CODH); acetyl-CoA synthase condenses them into acetyl-CoA, which branches to acetate, alcohols and biomass. 3. **Pressurized gas dissolution (Hollow-Fiber Membrane Biofilm Reactors):** - hydrogen and CO2 are poorly soluble in water; hollow-fiber membrane biofilm reactors (HfMBR) deliver the gases bubble-free at mild pressure straight into the biofilm growing on the fiber outer wall, lifting gas availability into the cells. --- ## Value chains and production pipelines ### Industrial pipeline of continuous microbial electrosynthesis of green acetic acid from renewable power and industrial CO2 (Sporomusa ovata biocathode, HfMBR reactor, membrane ultrafiltration, LIMS/EPD) ``` ┌───────────────────────────┐ ┌───────────────────────────┐ │ 1. Electroactive biofilm │ ───> │ 2. CO2 capture & feed to │ │ growth on the cathode │ │ the HfMBR electrolyser │ └───────────────────────────┘ └───────────────────────────┘ │ ▼ ┌───────────────────────────┐ ┌───────────────────────────┐ │ 4. Two-stage membrane │ <─── │ 3. Microbial │ │ ultrafiltration │ │ electrosynthesis of │ │ │ │ acetate under current │ └───────────────────────────┘ └───────────────────────────┘ │ ▼ ┌───────────────────────────┐ ┌───────────────────────────┐ │ 5. Acidification & vacuum │ ───> │ 6. Purity QC & LIMS/EPD │ │ rectification to glacial│ │ carbon-footprint passport│ │ acetic acid │ │ │ └───────────────────────────┘ └───────────────────────────┘ ``` #### Stage 1: Electroactive biofilm growth on the cathode A pure culture of *Sporomusa ovata* is grown anaerobically and pumped into the bioelectrochemical reactor, whose cathode is a high-area 3D carbon felt. Under a mild cathode potential the bacteria colonize the felt over several days, forming a thin conductive biofilm that will accept electrons from the electrode. #### Stage 2: CO2 capture and feed to the HfMBR electrolyser Dry CO2 captured from cement- or steel-plant flue gas is compressed and fed into the hollow porous polypropylene fibers that thread the cell, while the IrO2-coated anode receives clean water. The reactor draws DC current from a neighbouring wind or solar farm. #### Stage 3: Microbial electrosynthesis of acetate under current At the anode, water oxidizes to oxygen and protons; the released electrons travel through the external circuit to the cathode, where the *Sporomusa* biofilm takes them up and reduces the CO2 diffusing in from the fibers. Via the Wood-Ljungdahl pathway the cells steadily release acetate into the broth; pH is held near neutral by alkali dosing and the sodium-acetate broth is drawn off continuously. #### Stage 4: Two-stage membrane ultrafiltration The broth passes through a two-stage membrane plant: ceramic ultrafiltration retains and recycles the cells back to the reactor, and nanofiltration separates acetate salts from the residual mineral salts of the medium. #### Stage 5: Acidification and vacuum rectification The concentrated sodium acetate is acidified to liberate free acetic acid and sent to a vacuum rectification column; running under reduced pressure drops the boiling point, avoiding thermal degradation and saving energy, and leaves glacial acetic acid in the reboiler. #### Stage 6: Purity QC and LIMS/EPD carbon-footprint passport Each batch is checked by GC-MS for acetic-acid titre and trace metals, and coulombic efficiency is logged. The LIMS system certifies the product against food and chemical specifications and issues an EPD carbon-footprint passport showing the reduction versus the petrochemical route, after which the green acid is shipped.