Carbonate Mineral Precipitation for Soil Improvement Through Microbial Denitrification

ABSTRACT

Microbially induced carbonate precipitation (MICP) and associated biogas production may provide sustainable means of mitigating a number of geotechnical challenges associated with granular soils. MICP can induce interparticle soil cementation, mineral precipitation in soil pore space and/or biogas production to address geotechnical problems such as slope instability, soil erosion and scour, seepage of levees and cutoff walls, low bearing capacity of shallow foundations, and earthquake-induced liquefaction and settlement. Microbial denitrification has potential for improving the mechanical and hydraulic properties of soils because it promotes precipitation of calcium carbonate (CaCO₃) and produces nitrogen (N₂) gas without generating toxic by-products. We evaluated the potential for inducing carbonate precipitation in soil via bacterial denitrification using bench-scale experiments with the facultative anaerobe Pseudomonas denitrificans. Bench-scale experiments were conducted (1) without calcium in an N-rich bacterial growth medium in 2.0 L glass batch reactors and (2) with a source of calcium in sand-filled acrylic columns. Changes of pH, alkalinity, NO₃⁻ and NO₂⁻ in the batch reactors and columns, quantification of biogas production and observations of calcium-carbonate precipitation in the sand-filled columns indicate that denitrification led to carbonate precipitation and particle cementation in the pore water as well as a substantial amount of biogas production in both systems. These results document that bacterial denitrification has potential as a soil improvement mechanism.

KEYWORDS:

• Biogas
• carbonate precipitation
• denitrification
• microbially induced carbonate precipitation (MICP)

Funding

The authors are grateful for the funding by the Geomechanics and Geotechnical Systems, GeoEnvironmental Engineering and GeoHazards Mitigation program of the National Science Foundation (NSF) Division of Civil, Mechanical, and Manufacturing Innovation under grant number CMMI-0856801, “Microbially-Induced Cementation of Sands by Denitrification.” Any opinions or positions expressed in this paper are the opinions and positions of the authors only, and do not reflect any opinions or positions of the NSF.