China’s new fermentation system delivers 33% more biohydrogen while capturing carbon dioxide

Researchers in China have developed a new fermentation system that boosts biohydrogen production while capturing carbon dioxide.

Researchers from the Institute of Applied Ecology of the Chinese Academy of Sciences revealed that dark fermentation produces hydrogen gas from organic substrates under oxygen-free conditions, making it a promising route toward carbon-neutral hydrogen.

In practice, however, the process is often limited by the accumulation of volatile fatty acids, which decrease pH levels and suppress microbial activity.

Enhanced hydrogen yield

The team introduced wollastonite as a dual-function agent to simultaneously enhance H2 yield and capture CO2. “An optimal dosage of 10 g/L was identified, which shortened the lag phase from 23.13 to 12.38 h and increased the hydrogen yield from 158.11 ± 3.44 mL/g glucose-consumed to 210.75 ± 15.87 mL/g glucose-consumed,” said researchers in the study.

“Mechanistically, wollastonite buffered the system pH, steering metabolic flux away from lactate towards acetate synthesis by enriching Clostridium and suppressing Lactobacillus.”

Maximal CO2 capture

Researchers revealed that conventional pH control relies on alkaline chemicals such as sodium hydroxide, but these agents can cause localized pH spikes, progressive salinity buildup, and require continuous dosing — all without offering any added environmental benefit. Another challenge is that the resulting biogas contains a substantial fraction of carbon dioxide (CO2), which usually necessitates energy-intensive downstream separation. Together, these constraints make it difficult to efficiently produce hydrogen and mitigate carbon within a single system.

To address these limitations, the researchers introduced wollastonite (CaSiO3) as a dual-function additive. As acids accumulate during fermentation, they gradually dissolve the mineral, consuming protons and releasing calcium ions. This mechanism provides continuous, self-regulating pH buffering that stabilized the system at pH 6.5–7.0.

At an optimal dosage of 10 g/L, the lag phase of hydrogen production decreased by about 50%, and the specific hydrogen yield increased by roughly 33%, according to researchers.

“Wollastonite also enabled in-situ CO2 sequestration by precipitating it as CaCO3. However, maximal CO2 capture was achieved at a higher dosage (≥15 g/L), which passively reached the required neutral pH but compromised the hydrogen yield. This created a conflict with the optimal 10 g/L dosage for hydrogenesis,” said researchers in the study published in the Chemical Engineering Journal.

Researchers also found a trade-off between the two target functions. Efficient CO2 mineralization requires a neutral to slightly alkaline pH, which is achievable at higher wollastonite dosages (≥15 g/L), yet these conditions compromised hydrogen yield.

To decouple the two objectives, the researchers devised a two-stage strategy: the first stage uses the optimal 10 g/L dosage to maximize hydrogen output, while the second stage applies a post-fermentation pH adjustment to 7.0 to induce carbonation, according to a press release.

Using this approach, the system captured 0.49 ± 0.05 liters of CO2 per liter of medium and enriched the hydrogen content of the final biogas to 58.2 ± 1.1%. Solid-phase characterization confirmed that the captured CO2 was mineralized as calcite-phase calcium carbonate, a stable form suitable for long-term carbon storage, as per the release.

These results demonstrate the feasibility of integrating green hydrogen production with in-situ carbon capture within a single biorefinery framework, offering a practical approach to achieving negative-carbon biohydrogen production.