Introduction: Soil treatment

Soil treatment is a process to purify and revitalise soil by removing contaminants. Soil contamination is often caused by various chemicals (petroleum hydrocarbons, pesticides, lead, and other heavy metals), wastes such as alkali, oil, or some other non-degradable material. The main concern behind soil treatment is the harm to human health associated with direct contact with contaminated soil, vapours released by contaminants, and secondary contamination of water supplies. Contaminated soil can be treated using microbes, pH adjusters, organic amendments, and soil treatment technologies (biological, physiochemical, and thermal treatment).

The process of soil treatment is performed to make contaminated soil reusable for agriculture and other purposes. Soil contamination is often caused by various chemicals (petroleum hydrocarbons, pesticides, lead, and other heavy metals), wastes such as alkali, oil, or some other non-degradable material. 

These contaminants can be treated using microbes, pH adjusters, organic amendments, etc. Soil contamination can also happen as a result of leaking in underground storage tanks, leaching of waste or heavy metals from landfills, mining, and an abundance of other environmental issues that can also cause pollution of the soil. In polluted soil, moisture retention, aeration, and nutrients are compromised.

The Indian government has taken initiatives to conserve soil, like improving food cultivation techniques to satisfy the needs of a growing population. In many countries, the importance of soil treatment is not well-understood, thereby limiting their market. The introduction of new and sustainable technologies will lead to the growth of the market and boost trade in these countries.

Soil treatment methods

Soil treatment can be classified into three categories:

• Organic soil amendments (such as biofertiliser, crop yield residue, animal dung, and sewage residue or sludge)
• Key pH adjusters (including gypsum and agricultural lime)
• Soil preservation (pest and weed control)

Soil treatment technologies are also classified into three types—biological treatment, physicochemical treatment and thermal treatment.

Biological treatment

This is the most environmentally friendly method for remediating hydrocarbon and heavy metal contaminated soils. It includes the use of techniques like bio-sparging, phytoremediation, bioventing, and bioremediation.

• Biosparging: It is an in-situ remediation technique where oxygen and nutrients are supplied to chemically polluted soils to promote aerobic degradation of contaminants (often petroleum hydrocarbons) by indigenous microorganisms.
• Phytoremediation: It is a technique that uses plants to extract and remove elements pollutants from the soil and reduce their bioavailability in the soil.
• Bioventing: This is also an in situ remediation technique that degrades organic compounds by using microorganisms.
• Bioremediation: The process of removing contaminants and impairments of quality from soil and water by degrading, transforming, or breaking them down biologically.

Physicochemical treatment

This includes chemical oxygenation, fracturing, soil vapour extraction (SVE), electric resistance heating (ERH), solidification, and stabilisation.

• Electrical resistance heating (ERH): It is an in-situ environmental remediation technique. In this method, contaminants from the soil and groundwater are removed using the flow of alternating current electricity.
• Chemical oxygenation: This refers to the use of strong oxidants to accelerate degradation reactions in the treatment zone by injecting them into the area or mixing them mechanically.
• Soil vapour extraction (SVE): This technique is used to decontaminate the unsaturated zone of the soil. It is usually an in situ technology but can be used as an ex-situ also. The soil is vacuumed to induce controlled airflow to remove volatile and semi-volatile organic contaminants from the soil.

Thermal treatment or desorption

It is a remediation method used to clean contaminated/ polluted soils. As this method relies on heat to vaporise the contaminants, it can only be used on volatile contaminants.

Conclusion

Soil treatment refers to the process of balancing soil acidity and baseness. It is also defined as a process of removing pollutants from the soil to protect both the environment and people’s health. It balances soil acidity and baseness, purifies and revitalises the soil. The main concern behind soil treatment is the harm to human health associated with direct contact with contaminated soil, vapours released by contaminants, and secondary contamination of water supplies. So, the contaminated soil can be treated using microbes, pH adjusters, organic amendments, and soil treatment technologies (biological, physiochemical, and thermal treatment).