C0SMOS: Results of the first series of experiments

In this first series of COSMOS-experiments we focus on the process that probably will have the most severe impact on possibly present microbes, the lack of space. BC is a plastic clay and it is expected that (re)consolidation will fill voids and close fractures rapidly. Consequently, density and porosity will be restored to their initial state in a relative short time period. Porosity will therefore be a parameter that returns relatively fast to its initial state. As the BC pore-size at the underground Mol site (i.e. consolidated conditions, consolidation pressure of about 24 bar) follows a log-normal distribution with peaks around 60 nm and connecting pore throats that are on average smaller than 10 nm (Hemes, Desbois et al. 2015), it is more than likely that space/transport restriction will be among the first physico-chemical conditions to have an effect on the microbiological presence and activity. The lack of space is mimicked in the COSMOS experiments by the gradual (re)consolidation of a BC-BCPW slurry up to the current in situ consolidation pressure of Boom Clay at the HADES laboratory level, corresponding with a BC density of about 1.99 [g.cm-3]. During this (re)consolidation process the nitrate reducing prokaryotes (NRP) are given the necessary nitrate, functioning as electron acceptor, and acetate, mainly functioning as electron donor and possibly also partly as carbon source (C-source), to allow them to grow and/or proliferate.