One potential design for a geological disposal facility (GDF) for intermediate level radioactive waste (ILW) involves the use of a cement base grout which will establish a highly alkaline environment for extended time periods [1]. Methane generation by colonising microbes could impact the long-term performance of the facility by influencing gas pressures and potentially leading to the migration of 14C to the biosphere [1]. Sediments acquired from a wide-range of anthropogenic alkaline sites in the UK were used to develop acetoclastic and hydrogenotrophic methanogen enrichment cultures over a broad range of pH values (7.0–12.0). The generation of methane from hydrogen and acetate was assessed to determine the dominant methanogenic pathways. Archaeal community analysis via Illumina MiSeq was employed to describe the populations involved and the acetoclastic inhibitor methyl fluoride was utilised to confirm the lack of acetate-dependent methane generation under alkaline conditions. High pH (pH>9.0) microcosms employing alkaline sediments were dominated by hydrogen-consuming methanogens of the orders Methanobacteriales and Methanomicrobiales, with no acetate consumption detected under these conditions. In contrast, neutral pH microcosms employing control sediments were dominated by acetoclastic methanogens of the order Methanosarcinales and demonstrated high acetate consumption rates. The rate of acetate consumption and proportion of acetoclastic methanogens decreased in a linear fashion as the pH within cultures was increased, however hydrogen consumption rates remained stable up to pH 11.0. The data shown suggests hydrogenotrophic methanogenesis is the dominant methanogenic pathway at high pH which could have important consequences on gas pressures within a GDF.

  • This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Article metrics loading...

Loading full text...

Full text loading...

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error