Biological stabilization of soil simply refers to the stabilization of soil is achieved through biological means like planting or afforestation or more complex biological processes. The term “soil stabilization” refers to the process of increasing the stability and bearing capacity of the soil using proportion, controlled compaction, and/or the addition of suitable admixtures or stabilizers. Mechanical improvement and chemical treatment are the two other main techniques used to create engineered soil.
Mechanical improvement to enhance the quality of the soil covers consolidation, drainage, and other techniques in addition to compaction. Chemical treatments have been using chemicals and emulsions as binders, water repellents, and compaction aids that start chemical processes like pozzolanic reactions or soil hydration to produce artificial binding.
Importance of Biological Soil Stabilization
Increasing demand for usable land for developments necessitates exploring alternate techniques for ground and soil treatment. Especially, methods should have minimal impact on the environment at the same time enables the recycling of factory byproducts.
- The disposal of fly ash from thermal power industries has been a difficult problem that urgently needs a solution.
- The availability of limestone is very less
Finding a reliable and environmentally friendly alternative binder, such as cement, is thus required.
6 Methods of Biological Stabilization of Soil
1. Biological Stabilization of Soil with Bio enzyme
Biological catalysts called Bio-enzymes catalyze chemical interactions in the surface soil, increasing soil density and decreasing water retention and develops a layer that is dense, firm, and water-resistant. For bio-enzymes to function properly, the soil must contain a certain quantity of clay.
Mechanism of Bioenzyme in Soil
Bio-enzymes stabilize the soil via the following mechanisms.
- When bio-enzymes are added to the soil, they bind to the clay grid and release cations, reducing the thickness of the diffuse double layer of clay.
- The interaction between soil’s small clay particles and large organic molecules is catalyzed by the addition of bio-enzymes. The broad flat surfaces of large organic molecules cover the surfaces of smaller clay particles, neutralizing their negative charges and lowering the hygroscopicity of clay. The soil is prevented from absorbing any more water or losing any more density by this covering effect.
2. Biocementation for Biological Soil Stabilization
Calcium carbonate is deposited as a result of the ecological process known as biocementation, which is based on the Microbially Induced Calcite Precipitation mechanism.
Using calcite (CaCO3), which binds soil particles together and increases soil strength and stiffness, this technique makes use of the metabolic processes of bacteria. The most popular bacteria for the MICP process are Bacillus pasteurii or Sporosarcina pasteurii because of their high urease activity, which allows them to produce large amounts of precipitates quickly.
Mechanism of MICP in Soil for Biological Stabilization
When living things produce minerals, the process is known as biomineralization. Biomineralization happens as an unintended by-product of bacterial metabolism. These minerals might be silicates in algae and diatoms, carbonates in invertebrates, and invertebrates.
As a result of ion exchange, carbonate nucleation takes place. Another mechanism uses extracellular macromolecules that can trap calcium ions or occasionally act as growth promoters to control crystallization.
3. Biological soil Stabilization through Bioencapsulation
Bioencapsulation is a soil stabilization method which is a widely used traditional treatment of soil. The most effective way to transform clay wastes from dredged or excavated sites into high value building materials is through bioencapsulation. Aerobic urease-producing alkaliphilic bacteria like Bacillus sp. VS1 is the most frequently used bacteria for the MICP process.
Mechanism of Bioencapsulation in Soil
The bioencapsulation process works by using the enzyme activity of bacteria that produce urease to precipitate Calcite (CaCO3) from a Calcium Salt solution as well as urea (UPB).
A cemented product is produced as a result of the UPB cells’ enzymatic hydrolysis of urea, which raises pH in both the micro-gradient and overall range, releases carbonate, crystallizes calcite, and releases carbonate. It is evident that the nucleus was formed with a softer inner shell and a much firmer outer shell.
4. Biological strata Stabilization using Biocrusting
The process to create an organic or mineral crust on the soil’s surface to prevent water infiltration, dust emission, and erosion is called Biocrusting. Lichens, mosses, liverworts, cyanobacteria, and other small but significant organisms may be found in communities known as Biological Soil Crusts (BSCs), which are closely linked to the mineral soil surface and form a thin, cohesive layer.
Mechanism of Biocrusting in Soil
In the early stages of biocrust development, moss-dominated biocrusts can form if the initial soil-stabilizing cyanobacterial-dominated succession stages are skipped. Soil characteristics alter as biocrusts recover naturally. For instance, the amount of organic matter and nutrients in the soil increases. Furthermore, as biocrusts develop, the silt and clay levels in encrusted soils rise.
This phenomenon may be caused by two different mechanisms: first, biocrusts may trap fine soil particles; second, weathering of the preexisting substrate may produce new, smaller soil particles. Finally, biocrust has an impact on soil hydrology, with surface soil moisture content rising with biocrust succession.
5. Biological ground stabilization through Bioclogging
Reduced soil porosity and hydraulic conductivity are achieved through bioclogging, which is the microbial production of pore-filling materials. Microaerophilic and facultative anaerobic bacteria are the best microorganisms for bioclogging the soil.
Mechanism of Bioclogging in Soil
Microbial biomass, which includes the bodies and byproducts of microorganisms like calcite (CaCO3), blocks the pore spaces in a soil mass. The soil will become more water-impermeable as bacterial biomass, insoluble bacterial slime, and poorly soluble biogenic gas bubbles build up.
One application that continues to improve is the formation of soil plugs by Bacillus pasteurii in a medium containing urea and calcium chloride. The urease enzyme, which hydrolyzes urea, is produced by bacteria. Hydro carbonate is developed and the pH is raised as a result of this enzymatic reaction. Calcium carbonate is beginning to precipitate, filling up the pores and linking soil particles together.
6. Biological soil stabilization using Bioremediation
The term “bioremediation” refers to the process of utilizing biological processes to primarily avoid contamination or other quality-related problems from soil and water. In a natural process called bioremediation, contaminants are changed by bacteria, fungi, and plants as they go about their daily lives.
(Source – Bioremediationinfo)
Mechanism of Bioremediation in Soil
With the help of the nutrients in the soil, naturally occurring microorganisms like algae, bacteria, and fungus, bioremediation oxidize and hydrolyze the contaminants present in the soil. These nutrients could be present in the soil naturally or artificially introduced using techniques like biostimulation. To clean up contaminated soils, biostimulation also makes use of local microbial populations.
This metabolic process aids in the treatment and elimination of the toxic pollutants in the soil. The target contaminant is metabolized by the microbes into usable energy through oxidation-reduction reactions, which the microbes use as an energy source in the soil. By-products that are released in the environment are generally less toxic than parent contaminants.