Microbial transformation of upper aquifers loamy rocks under complex pollution during in situ bioremediation

Abstract

The study investigated biogenic modifications in loamy rocks following a single stimulation of microbial activity in groundwater through the application of milk whey at a depth of 10–14 m in proximity to a radioactive waste storage facility, within a nitrate-polluted area near the Siberian Chemical Combine (Seversk, Tomsk Region). The consumption of nitrate ions and the establishment of anaerobic conditions via microbial denitrification were completed within 45 days of the in situ experiment. Milk whey served as an effective source of organic carbon (C), calcium (Ca), and phosphorus (P) for in situ bioremediation processes. Observed phenomena included the accumulation of carbonate minerals, reduction of iron and sulfate ions, and the formation of sulfide-iron phases. The release of iron from aluminosilicate mineral phases under anaerobic conditions resulted in partial mineral dissolution and the formation of amorphous silica. Subsequent phase analysis revealed the presence of crystalline iron sulfide forms, exhibiting compositional similarities to pyrrhotite and troilite. Laboratory experiments demonstrated that the absence of sulfate in the system led to a significant decrease in iron content within the solid phase, accompanied by a redistribution of remaining iron from silicate mineral matrices to amorphous phases associated with organic matter. Conversely, the presence of sulfate facilitated activity of sulfate-reducing bacteria and the accumulation of iron sulfide phases. The biogenic formation of authigenic mineral phases constitutes a critical factor in the development of a sedimentary mineral barrier, which is essential during complex groundwater contamination involving radionuclides and heavy metals.