Microbially Induced Calcite Precipitation (MICP)

Microbially induced calcite precipitation (MICP) is a bio-mediated mineralization process in which the metabolic activity of microorganisms raises the carbonate saturation state of a local pore solution, causing calcium carbonate (calcite, CaCO₃) to precipitate. When that precipitation occurs inside a granular medium — sand, soil, fractured rock, porous stone or concrete — the newly formed calcite acts as a cement that binds grains together.

MICP is a mainstream technique in geotechnical engineering, applied microbiology and heritage conservation. It is studied for soil stabilization, ground improvement, erosion and dust control, and crack healing in concrete and stone. It is distinct from abiotic grouting because the reaction is driven by living organisms and can be delivered as a liquid treatment that sets in place.

How it works

The general mechanism has three coupled parts:

1. A microbial metabolism that shifts carbonate chemistry. The best-studied route is ureolysis, in which ureolytic bacteria hydrolyse urea and raise both pH and dissolved inorganic carbon. Other routes include denitrification and ammonification, which are studied where urea-based treatment is undesirable.
2. A calcium source. Dissolved calcium, typically supplied as calcium chloride or calcium lactate in a feed solution, provides the cation.
3. Supersaturation and nucleation. The combined shift in pH, carbonate concentration and calcium concentration pushes the pore solution past saturation with respect to calcium carbonate. Calcite nucleates on grain surfaces and grows, bridging contacts between particles.

The result is a cemented granular mass whose mechanical properties depend on how much calcite was precipitated and where it formed. Precipitation concentrated at grain contacts contributes disproportionately to strength; precipitation coating grain surfaces contributes more to permeability reduction.

Delivery

In practice, MICP treatment is usually applied as a sequence of injections: a bacterial suspension is introduced into the medium so that cells attach to grain surfaces, followed by a feed solution containing urea and a calcium salt. The feed is supplied over multiple cycles, with retention periods between them, until the desired calcite content is reached. The number of cycles, the concentration of the feed, and the retention time are the main controllable parameters.

What MICP is not

• It is not the same as enzyme-induced carbonate precipitation (EICP), a cell-free variant that uses extracted urease rather than whole bacterial cells. See Enzyme-Induced Carbonate Precipitation (EICP).
• It is not a claim of unlimited or anomalous material behaviour. Its effects are measurable by ordinary geotechnical and chemical means: calcium carbonate content, unconfined compressive strength, permeability, and shear wave velocity.

Evidence status in this wiki

The concept is described here from the general published literature. The source dossier that prompted this page — Microbially Induced Calcite Precipitation: The source archive Materials Dossier (Provisional Record) — could not be read in full at the time of writing, and its capture audit recorded a high probability of extraction problems. No specific numbers, strains, protocols or results from that dossier are reproduced on this page. See Patent as Evidence for how Bench treats patent and commercial claims that may appear alongside research results in archive dossiers.

Related

• Ureolysis-Driven Carbonate Precipitation — the urease-driven biochemical route.
• Bio-Cementation — the engineering applications.
• Calcium Carbonate (Calcite, CaCO₃) — the precipitated mineral.
• Enzyme-Induced Carbonate Precipitation (EICP) — the cell-free variant.
• construction and chemistry — topic guides.
• Rinsing Out the Ammonium: A 3.7-Metre Test of By-product Removal After Ureolytic Bio-Cementation (Lee et al., 2019) — a 2019 column study of whether the ammonium by-product of ureolytic MICP can be rinsed out of treated sand at 3.7-metre scale.
• Is Biocement Actually Green? A 2021 Life Cycle Assessment of Six Microbial Routes to Calcium Carbonate (Porter et al.) — a 2021 life cycle assessment comparing six metabolic routes to MICP with industrial calcium carbonate; it reports that the purity of the purchased reagents, calcium chloride above all, largely decides whether the engineered process comes out ahead.
• Calcite Without Urea: An Asparaginase-Driven Bio-Grout for Sand (Li et al., 2015) — a 2015 laboratory example of the ammonification route: asparaginase-driven calcite cementation of small sand columns, compared with a urease-based grout.
• Not Always Calcite: How Three Sporosarcina Strains Produced Different Calcium Carbonate Phases (Clarà Saracho et al., 2020) — a 2020 study showing that the precipitate is not always calcite: under the same treatment, three Sporosarcina strains yielded calcite, calcite with vaterite, or amorphous calcium carbonate, which the authors link to differences in urease kinetics and pH.