Eco-friendly soil treatment and stabilization by Microbial Induced Calcite Precipitation

RESEARCH PROPOSAL
Eco-friendly soil treatment and stabilization by Microbial Induced Calcite Precipitation
Abstract
This study will be carried out to establish the ecofriendly techniques that can be used in the
treatment and stabilization of soil. This study in its complex employs a number of techniques,
the methodologies, and the chemicals used to make the process a success and at end of it
gather nearly of definitely positive results. This study directs its focus on mainly the
ecofriendly method of soil stabilization by Microbial Induced Calcite Precipitation (MICP).In
the previous research there is increment in the shear strength and other properties of groups
of soil when concentration of bacteria is 1% to 4%. This technique has shown significant
increase of shear strength in the clay soil, with injection of bacteria (Sporosarcina Pasteurii)
using urea hydrolysis to influence the natural calcium precipitation process of bacteria. This
study entails an experiment of metabolic pathway of bacteria utilized to induce calcite
precipitation throughout the soil mass. To analyze the increase in strength approximately; 1%
to 3% concentration of these bacteria is used. The MICP requires bacterial growth at
laboratory scale along with nutrients in the formation of bio slurry. The basic parameters
likewise shear strength and maximum dry density (MDD) of the soil matrix were observed
before and after treatment. These findings will enable the researcher to draw the conclusions
and the recommendations of the study.
Keywords include; Microbial Induced Calcite Precipitation (MICP), Ecofriendly.
Introduction
As we have seen construction on weak soils is inevitable as the quantity of suitable lands in
diminishing due to global construction demands thus weak soils must be stabilized in order to
help overcome this problem these have been characterized as having low strength and high
compressibility and have consolidation. These soils occur in many areas which are filled with
clay and silt intermixed with sand and also in tropical zones which are connected to water
which cause them to have soft strata and high compressibility and liquify under loads and
consolidate which causes major problems in constructed buildings. As time passes we need to
improve our soil improvement techniques as the addition of chemical and cementitious grout
has proven to improve soil properties but it has major adverse effect in the ecosystem and it
contaminates soil and groundwater which is harmful for environment down the road this
hazardous characteristics must be rectified by a relatively green and sustainable techniques.
One such technique is the usage of bacterial improvements in soil matrix or microbial
induced calcite precipitation (MICP) has been introduced in recent years. This technique
relies on biochemical process to improve the soil and its engineering properties (MDD. shear
strength). The application of this technique is diverse as it can be applied in concrete strength
and durability and brick durability and improve impermeability of materials.
The bacteria in question called Sporosarcina Pasteurii this bacterium when comes in contact
with chemical reagent or bio grout excretes calcite precipitation which harden after some
time and causes cementation between soil particles but this technique requires bacteria to be

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mixed in soil mass and them a curing period to be done to soil mass so that bacteria can use
its urease hydrolysis and start the cementation process for the soil and this is relatively how
MICP process works.
Review and theoretical literature
How Microbial Induced Calcite Precipitation works
Microbial induced calcite precipitation is a bio- geochemical process that induces calcium
carbonate precipitation within the soil matrix. Biomineralization in the form of calcium
carbonate precipitation can be tracked back to the Precambrian period. The main groups of
microorganisms that can induce the carbonate precipitation are photosynthetic
microorganisms such as cynobacteria & microalgae; sulfate reducing bacteria and some
species of microorganisms involved in nitrogen cycle.
Fig: 1 Diagram of calcite cementation occurring at grain to grain contacts
In particular, Sporosarcina pasteurii (Bacillus pasteurii) has been found to be a very effective
producer of urease and an effective inducer of calcite deposition Sporosarcina pasteurii
(Bacillus pasteurii) is ideally suited for larger scale activities, such as rammed earth
construction, because of its ability to survive desiccation through In addition, Sporosarcina
pasteurii (Bacillus pasteurii) has proven to be a good candidate for microbial induced calcite
precipitation of sandy soils due to its tendency not to
aggregate, thereby allowing for thorough dispersion throughout the soil structure.
Furthermore, the size of these microbes allows them to move freely through granular sandy
and silty material. The urease enzyme supplied directly into soil or produced insitu by
bacteria, decompose urea (CO (NH2)2) in the soil through a chemical reaction known as
hydrolysis of urea:
Urease Hydrolysis:
CO (NH2)2 + 2H2O 2NH4++ CO 2- .... (1)
The ammonium (NH4+) released from the urea hydrolysis results in a local pH rise that
commences the precipitation of calcium carbonate (calcite). Calcite is precipitated through
the reaction between carbonate ions (CO 2-) from the urea hydrolysis and calcium ions
(Ca2+) from the supplied calcium chloride:
Ca2+ + CO 2- CaCO ...... (2)
The calcite (CaCO3) formed is responsible for improving the engineering properties of
soil.

Soil Sample
Soil sample was collected from just behind the Mehran university civil engineering
department from the department the site of excavation is about 100ft away then
representative sample was gathered by quartering method.
Fig: 2 Representative soil Sample
Preparation of Nutrient solution and Reagent solution:
Preparation of Nutrient solution for producing the calcite the reagent use in MICP
is urea & calcium chloride. In terms of 1 lit. Volume of distilled water the equal
ratio of 0.5M of urea(CO(NH2)2) and calcium chloride(CaCl2) is essential inorder
to achieve complete production of calcite. For preparation of Nutrient solution
urea and calcium chloride is mixed with broth solution & cultivated bacteria were
released into the nutrient solution.

Fig 4: Urea [CO(NH2)2]
Fig 5: Calcium Chloride (CaCl2)
Fig 6: 0.5M per liter constituent of urea and calcium chloride (30.03 g urea, 55.49 g
calcium chloride)
EXPERIMENT STUDY
Test Sample preparation:
In this study, shear strength and compressive strength properties of soil were firstly
determined in the natural form of soil. Liquid limit test, plastic limit, Dry density through
modified Procter test., direct shear test, were also be carried out of natural soil.
Then bacterial solution and reagent solution was added in specific percentages (1%, 2% and
3%) by weight of the sample required for different test we added the test samples were all of
each of 5kg weight. The bacteria were added in 50ml, 100ml and 150ml solution respectively
to each sample. The three samples were given 1 litre reagent solution each at first curing to
allow reagent solution to enter soil matrix fully so as to allow bacteria to easily access it and
start its natural process of carbonation.
After the addition of Bacterial solution with specific percentage (1%, 2% and 3%) by
weight, the modified proctor test and shear box test were carried out on test samples to
determine the change in properties observed by the MICP technique.
b) Curing of Test Samples:
When the bacterial solution and reagent solution are added to soil matrix it does not give
results directly the bacteria need some time to grow and excrete calcium carbonate and thus
this process takes time and reagent solution is to be applied constantly for 7 days with
refilling of each test sample after every 12 hours. We were able to use almost 8 liters of
reagent solution in 7 days for 3 test samples of 5 kg each