This post is essentially a summary and review of a new paper published in Frontiers in Microbiology that reviews the process and applications of microbially induced calcite precipitation (MICP). The paper is an extensive review of MICP research. MICP offers an effective alternative to the use of Portland cement for soil stabilization. The process is also known as bio-cementing. The process is described below from the paper’s abstract:
‘The process utilizes the urease activity of ureolytic
bacteria, most commonly Sporosarcina pasteurii to convert soluble urea and
calcium to solid calcite in the pore space of granular media, providing
cementation, impermeability reduction and contaminant sequestration without
excavation or heat.”
As the graphical abstract below
shows, MICP has six distinct engineering applications: 1) soil stabilization,
2) self-healing concrete, 3) erosion control, 4) liquefaction mitigation, 5)
wellbore sealing, and 6) heavy metal remediation. These are all very useful to
societies. As the timeline in the graphic shows, commercial product development
began in 2021.
The Graphics below show the basic chemistry of MICP.
Factors controlling MICP treatment
efficiency include concentration of urea and calcium, temperature, soil pore
structure, soil grain size, the number of cycles, and treatment time.
The graphic below shows the
maturity of each application, with soil stabilization being fully mature and
CO2/wellbore sealing being the least mature application.
Soil Stabilization
Early experiments in 2006 showed
that MICP increased shear strength and stiffness in triaxial specimens of
treated sand. Experiments in 2012 showed that:
“…multiple cycles of dilute treatment are more
homogeneous in cementation than a single cycle of high concentration; this is
relevant for the design of an injection strategy.”
The table below shows the
advantages in unconfined compressive strength (UCS) conferred by MICP.
Erosion Control and Dust Suppression
MICP clearly aids erosion control
by holding the soil substrate in place when exposed to water and wind. It also
clearly aids dust suppression at construction sites, which can be problematic.
“…the low-viscosity treatment solutions percolate into
sandy surfaces by gravity without equipment or excavation, while the resulting
calcite crust is mechanically resistant, and hydrologically transparent
(compared to a cement-based surface sealer).”
MICP has been applied to coastal
sandy slopes and employed along with vegetation. However, it was found that
seeding must be delayed at least a few weeks after MICP is applied due to
initially high ammonium levels, which inhibit germination. These dissipate
after a few weeks.
Self-Healing Concrete
MICP is an effective method of
providing self-healing concrete. The activated bacterial spores can seal cracks
in concrete. Hydrogel beads are utilized to keep the spores viable. The graphic
below illustrates the process.
Heavy Metal Immobilization
MICP deployed as bioremediation is
proven to chemically immobilize heavy metal contaminants. One lab experiment
showed:
“…98.3% lead and 85.4% cadmium removal within 48 h
through MICP from contaminated soil matrices. The mixture exhibited
synergistic benefits including enhanced urease activity, greater metal
resistance, and increased calcite precipitation making it a more effective and
sustainable bioremediation strategy for soils affected by mining and industrial
activities.”
The solidification of mine
tailings is another application that immobilizes heavy metal transport.
Liquefaction Mitigation
Soil liquefaction due to
earthquakes has been an intense field of research for biocementation.
Experiments in 2011 found that:
“…the liquefaction resistance of the indigenous
ureolytic community could be stimulated in place to provide measurable
increases in shear wave velocity.”
However, they do note that
denitrification has advantages over MICP in liquefaction mitigation, and that
it is :
“…more practically viable at the target depths (usually
2–15 m) than ureolysis-based injection because it does not have the bacterial
filtration limitation.”
Wellbore Sealing and CO2 Sequestration
Carbonate mineralization has long
been known as a carbon sequestration method. CO2 can be held in the cement as
carbon in its chemical structure. Biocementation has emerged as a viable method
of sealing abandoned wellbores, some of which are difficult to seal due to
their aging and failing components. It can also be used in CO storage wells.
For well sealing, biogenic calcite can plug microchannels of the previously
cemented wellbores and annular voids that are leakage pathways.
Applications Summary
The table below summarizes the applications of MICP.
Scale-Up Challenges and Recent Advances
The main scale-up challenge in
MICP is treatment uniformity.
“…preferential flow in a heterogeneous soil produces
zones of over-treatment and untreated zones that are intrinsic to any of the
injection-based techniques and more pronounced in the case of MICP as the
biological reaction is spatially sensitive to the density of bacteria (Whiffin
et al., 2007; Mujah et al., 2017; Fu et al., 2023).”
The graphic below shows treatment
uniformity and effective depths for different injection strategies.
Recent advances include novel
microorganisms and alternative pathways, hybrid and composite MICP techniques,
additive manufacturing and 3D bioprinting, and machine learning and data-driven
optimization.
They note that self-healing
concrete is a more mature technology than the geotechnical applications of
MICP. This is mainly because self-healing concrete can be manufactured in a
controlled environment, while treating soil substrates involves dealing with
the natural heterogeneity of soils. Relative technology readiness for
applications of MICP is shown below.
References:
Microbially
induced calcite precipitation (MICP): mechanisms, engineering applications, and
pathway to field-scale deployment — a comprehensive review. Tao He, Jiaxing
Chen, and Xiyan Lou. Shangqiu Normal University, Shangqiu, Henan, China. Frontiers
in Microbiology. Microbiological Chemistry and Geomicrobiology. Volume 17 – August,
2026. Frontiers | Microbially induced
calcite precipitation (MICP): mechanisms, engineering applications, and pathway
to field-scale deployment — a comprehensive review
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