Evaluating the extent of microbially-induced glass alteration by a subsurface Paenibacillus bacterium

Silicate glasses are an accepted option for immobilizing nuclear waste and waste glass can be disposed in near-surface environments. It is important to understand glass alteration mechanisms under site-relevant conditions to predict glass corrosion rates upon disposal. Microbial activity near the glass surface may influence glass alteration. However, waste glass chemical durability is currently evaluated without consideration of microbial alteration. Here, four glass compositions were tested in three solutions, with and without a subsurface Paenibacillus bacterium, to compare the extent of glass leaching. Results indicate that the Paenibacillus cells increased glass alteration, resulting in higher concentrations of boron, iron, sodium, and silicon released into solution. The combination of microbially mediated organic acid production, which decreased pH, and glass dissolution, which increased pH, resulted in a net neutral or slightly acidic solution that could promote further glass alteration. The amount of each element released depended on glass composition and solution chemistry. This study revealed the dynamic relationship between microbial metabolism, elemental release, and corresponding changes to solution pH, showing that microbial processes can indirectly accelerate glass alteration. This work supports a greater understanding of microbially-influenced glass alteration and informs development of standardized durability tests to assess microbial influence at disposal facilities.