# Impact of Polyethylene-Glycol-Induced Water Potential on Methane Yield and Microbial Consortium Dynamics in the Anaerobic Degradation of Glucose

## TL;DR

This study shows that water stress caused by cations, not their direct toxicity, inhibits methane production in anaerobic digesters.

## Contribution

The study reveals that cation-induced inhibition of methane production is primarily due to water stress, not direct toxicity.

## Key findings

- Methane potential decreased significantly as water potential (Ψ) dropped from −0.92 to −5.10 MPa.
- Acetoclastic Methanosarcina decreased while hydrogenotrophic Methanoculleus and Methanobacterium increased with lower Ψ.
- Changes in microbial communities under PEG-induced Ψ mirrored those under cation inhibition with KCl.

## Abstract

This study investigated the relationship between water potential (Ψ) and the cation-induced inhibition of methane production in anaerobic digesters. The Ψ around methanogens was manipulated using polyethylene glycol (PEG) in a batch anaerobic reactor, ranging from −0.92 to −5.10 MPa. The ultimate methane potential (Bu) decreased significantly from 0.293 to 0.002 Nm3 kg−1-VSadded as Ψ decreased. When Ψ lowered from −0.92 MPa to −1.48 MPa, the community distribution of acetoclastic Methanosarcina decreased from 59.62% to 40.44%, while those of hydrogenotrophic Methanoculleus and Methanobacterium increased from 17.70% and 1.30% to 36.30% and 18.07%, respectively. These results mirrored changes observed in methanogenic communities affected by cation inhibition with KCl. Our findings strongly indicate that the inhibitory effect of cations on methane production may stem more from the water stress induced by cations than from their direct toxic effects. This study highlights the importance of considering Ψ dynamics in understanding cation-mediated inhibition in anaerobic digesters, providing insights into optimizing microbial processes for enhanced methane production from organic substrates.