Soil and Land Treatment
Types of Land Treatment
Soil Treatment or Land treatment refers to the removal of contaminant from soil either on site or away from the site of contamination.
Bio-remediation - The use of biological mechanisms to destroy, transform, or immobilize environmental contaminants in order to protect potential sensitive receptors
Phyto-remediation - treatment with the help of plants
In-situ remediation techniques involve leaving the soil in its original place and bringing the biological mechanisms to the soil
Bioaugmentation is the applications of indigenous or allochthonous wide type or genetically modified microorganisms to polluted hazardous waste sites in order to accelerate the removal of undesired compounds. It is thought that bioaugmentation approach should be applied when the biostimulation and bioattenuation have failed.
Biostimulation is the addition of nutrients to a polluted site in order to encourage the growth of naturally occurring chemical-degrading microorganisms.
Bioattenuation is the method that relies on natural processes to dissipate contaminants through biological transformation
Bioventing is the only in situ bioremediation technique that allows for the treatment of unsaturated soil. Bioventing is not effective if the water table is within several feet of the surface. Uses a vacuum enhanced soil vapor extraction system. Due to the pressure gradient in the soil, atmospheric oxygen flows into the subsurface. This oxygen starts an aerobic contaminant decomposition process. In many cases it is necessary to add nitrogen salts as an additive by sprinkling a nutrient solution on top of the soil or by injecting them into the soil above the contaminated soil zone.
Biosparging is the injection of atmospheric air into the aquifer. It is used in both saturated and unsaturated soil zones
Bioslurping is a unique in situ treatment technique in that it also treats free product phases floating on top of the groundwater
Phytoremediation is the direct use of green plants and their associated microorganisms to stabilize or reduce contamination in soils. Sites with low concentrations of contaminants over large cleanup areas and at shallow depths present especially favorable conditions for phytoremediation.
Plant species are selected for use based on factors such as ability to extract or degrade the contaminants of concern, adaptation to local climates, high biomass, depth root structure, compatibility with soils, growth rate, ease of planting and maintenance, and ability to take up large quantities of water through the roots
Phytodegradation: use of plants to uptake, store and degrade contaminants within its tissue
Phytostimulation or rhizodegradation: use of rhizospheric associations between plants and symbiotic soil microbes to degrade contaminants.
Phytovolatilisation: use of a plant's ability to uptake contaminants from the growth matrix and subsequently transform and volatilise contaminants into the atmosphere
Phytoextraction: use plants to absorb, translocate and store toxic contaminants from a soil matrix into their root and shoot tissue
Rhizofiltration: use of roots to uptake also store contaminants from an aqueous growth matrix
Phytostabilisation: plant-mediated immobilisation or binding of contaminants into the soil matrix, thereby reducing their bioavailability.
Ex situ remediation techniques involve removing the soil from the subsurface to treat it
Composting consists of excavating the soil and then mixing organics such as wood, hay, manure, and vegetative waste with the contaminated soil. The organics are chosen based on their ability to provide the proper porosity and carbon and nitrogen balances to aid in the breakdown of contaminants. Maintaining thermophilic temperatures 54 to 65 degree C is an important part of composting. In most cases, the indigenous microorganisms maintain this temperature while degrading the contaminant. Composting is most effective when removing PAH, TNT, and RDX.
It is a process in which the soil is excavated and mechanically separated via sieving. The polluted soil is then place in layers no more than 0.4 meters thick.. Oxygen is added and mixing occurs via plowing, harrowing, or milling. Nutrients and moisture may also be added to aid the remediation process. The pH of the soil is also regulated (keeping it near 7.0) using crushed limestone or agricultural lime.
Excavated soils are mixed with soil amendments and placed in aboveground enclosures. It is an aerated static pile composting process in which compost is formed into piles and aerated with blowers or vacuum pumps. Soil is piled, nutrients, microbes, oxygen, and substrate are added to start the biological degradation of the contaminants. Nutrients such as mineral fertilizers may also be added. Additionally, microorganisms such as fungi, bacteria, or enzymes could be added.
Bioreactors are also used depending on the amount of soil need to be treated.
Prevention of Soil Pollution
Prevention is always the most preferred option before the release of any contaminant in environment.