What Is Biological Methanation of Hydrogen? Power-to-Gas and Microbial CH4 Synthesis
Biological methanation of hydrogen is a power-to-gas process where hydrogenotrophic archaea (mainly *Methanothermobacter*) convert added renewable H₂ and the CO₂ already in biogas into methane, upgrading raw biogas to >95% CH₄ at 60–85% energy efficiency. In-reactor (in-situ) and ex-situ loop configurations let plants store surplus wind or solar electricity as pipeline-grade gas, raising biomethane output 30–60% without extra feedstock.
The Microbial Chemistry
The core reaction is CO₂ + 4H₂ → CH₄ + 2H₂O, catalyzed biologically rather than over a heated nickel Sabatier catalyst. Hydrogenotrophic methanogens use H₂ to reduce CO₂, thriving at thermophilic 55–70°C where rates are highest. Because biogas is already ~40% CO₂, feeding electrolytic H₂ directly into the gas loop converts that “waste” carbon into saleable methane while cutting the plant’s net CO₂ venting.
Comparative Data Table: In-situ vs Ex-situ Methanation
| Configuration | Where | Temp (°C) | CH₄ Purity | Complexity |
| In-situ (in digester) | Inside AD tank | 35–55 | 60–80% | Low |
| Ex-situ loop | External reactor | 55–70 | >95% | Medium |
| Ex-situ + upgrading | Reactor + scrubber | 55–70 | >97% | Higher |
Why It Matters for Biogas Plants
Methanation turns intermittent renewables into storable, pipeline-ready gas and lifts a plant’s biomethane yield 30–60% from the same feedstock. Ex-situ at 55–70°C reaches >95% CH₄ and pairs cleanly with membrane or cryogenic upgrading; in-situ is cheaper to add but yields lower purity. Either way the plant gains a flexible power-to-gas buffer that also lowers its carbon intensity—valuable under green-gas certification schemes.
Frequently Asked Questions (FAQ)
Q1: How does power-to-gas methanation work?
A: Surplus renewable electricity splits water into H₂ via electrolysis; that H₂ is fed with biogas CO₂ to hydrogenotrophic archaea, which reduce the CO₂ to CH₄. The result is pipeline-grade methane that stores intermittent wind or solar as gas.
Q2: What microbes convert hydrogen to methane?
A: Mainly hydrogenotrophic methanogens of the genus *Methanothermobacter*, which use H₂ to reduce CO₂. They perform best at thermophilic 55–70°C, where reaction rates and methane purity are highest.
Q3: What is the efficiency of biological methanation?
A: Energy efficiency runs 60–85%, counting electrolysis and the biological step. Ex-situ thermophilic reactors reach the top of that range and >95% CH₄ purity, versus 60–80% for simpler in-situ setups inside the digester.
Q4: Does methanation increase biomethane output?
A: Yes—by converting biogas CO₂ into methane, plants raise biomethane yield 30–60% from the same feedstock and gain a renewable-power storage buffer that also lowers carbon intensity for certification.