Soil remediation

Soil remediation is to remove pollution or contaminants (e.g., heavy metals, such as lead Pb, chromium Cr, arsenic As and cadmium Cd) from soil or sediment media. 

There are many soil remediation technologies. However they can be mainly categorised into: 
1. Ex-situ methods are excavation of affected soils and subsequent treatment at the surface.
2. In-situ methods deals with treatment of the contamination without removing the soils.

Remediation technologies can also be categorised:

Physical remediation

1. Thermal treatment - soil vapour extraction;

2. Soil washing.

Chemical remediation

1. Organic solvent extraction of organic contaminants, such as PCBs t from soils
2. Chemical oxidation - oxidants help to break organic contaminants down into harmless
     substances such as water and carbon dioxide.

Biological remediation -  a treatment process using microorganisms to break down, or degrade organic contaminants or toxic hazardous into less toxic or nontoxic substances, such as nitrogen N₂, carbon dioxide CO₂, and even water.

Phytoremediation -  in situ  use of plants to remediate contaminated soil, including
1. Rhizofiltration - accumulation of contaminants, such as toxic metals, by plant roots;
2. Phytoextraction - transportation and accumulation of contaminants, such as toxic metals, 
     in harvested plant shoots, trunks and leaves;
3. Phytotransformation - degradation of complex organic contaminants into simple
     molecules which are incorporated into plant tissues or are evaporated from plant tissues;
4. Phytostimulation - stimulation of microbial and fungal degradation by release of their
    exudates/enzymes around plant root zone

Phytoremediation is of:

1. Low cost,
2. Environmentally sound,
3. Equally protective of human health and the environment has been considered as a good
    alternative technique for cleaning contaminated soils.