Impact of Water Saturation on Microbial Hydrogen Consumption in Porous Media

TL;DR

This study explores how water saturation affects microbial hydrogen consumption in porous materials, which is important for understanding hydrogen behavior in geological waste storage.

Contribution

The first study to examine microbial H2 consumption in a natural, partially saturated porous medium.

Findings

H2 consumption rates increased with saturation, peaking at 90% saturation.

No H2 oxidation occurred below 70% saturation during the 90-day experiment.

The rise in consumption between 70% and 80% saturation is linked to pore saturation changes.

Abstract

Hydrogen (H2) production from steel corrosion
challenges
the long-term stability of deep geological repositories for radioactive
waste storage. Subsurface microbial communities are known to consume
H2, but previous work has primarily focused on fully saturated
porous environments. However, gas production will prevent full water
saturation of the repository tunnels, where microbial H2 consumption is expected. Here, we investigate H2 consumption
rates at four saturation levels in sand-bentonite, a candidate tunnel
backfill material for the Swiss repository concept. The rates ranged
from 0.14 μmol·d–1·cm–3
sand‑bentonite (at 70% saturation) to 2.23 μmol·d–1·cm–3
sand‑bentonite (at 90% saturation), exceeding those observed in fully saturated
environments. Throughout the 90 days of the experiment, no oxidation
was detected below 70% saturation. A sharp rise in H2 consumption
rate between 70% and 80% saturation reflected the reduced water potential
leading to saturation of small pores. This study is the first to examine
microbial H2 consumption in a natural, partially saturated
porous medium, an essential step toward accurately modeling H2 sinks as a function of repository saturation. Beyond nuclear
waste disposal, our findings may also inform strategies for subsurface
H2 storage.

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