Page 199 - Soil Degradation, Conservation and Remediation

188 6 Soil Pollution

Landfarming : In this technique, contaminated soil is excavated and spread over a
prepared bed and periodically tilled until pollutants are degraded. Indigenous
biodegradative microorganisms are stimulated which facilitate their aerobic
degradation of contaminants. The practice is limited to the treatment of superfi cial
10–35 cm of soil.
Composting : It involves combining contaminated soil with nonhazardous organic

ammendments such as manure or agricultural wastes. The presence of these
organic materials supports the development of a rich microbial population and
elevated temperature characteristic of composting.
Biopiles : Biopiles are a hybrid of landfarming and composting. Essentially,
engineered cells are constructed as aerated composted piles. Typically used for
treatment of surface contamination with petroleum hydrocarbons, they are a refi ned
version of landfarming that tend to control physical losses of the contaminants
by leaching and volatilization. Biopiles provide a favorable environment for
indigenous aerobic and anaerobic microorganisms (von Fahnestock et al. 1998 ).
Bioreactors : Slurry reactors or aqueous reactors are used for ex situ treatment of
contaminated soil and water pumped up from a contaminated plume. It involves
the processing of contaminated soil through an engineered containment system.

Phytoremediation

The use of plants for in situ treatment of pollutants in soils, sediments, and water is
known as phytoremediation. Phytoremediation is a relatively new technology that
offers clear advantages over traditional methods for site cleanup. Some of its
applications have only been assayed at the laboratory or greenhouse level, but
others have been field tested sufficiently to allow full-scale operational (Campos

et al. 2008 ). It is best applied at sites with relatively shallow contamination of
pollutants that are amenable to phytoextraction, phytovolatilization, phytodegradation,
and/or phytostimulation.
Phytoextraction : the uptake of contaminants in plant roots and their concentration
in harvestable tissues
Phytovolatilization : the uptake of contaminants by plants and their subsequent
release into the atmosphere in a volatile form
Phytodegradation : biodegradation of pollutants by plant enzymes
Phytostimulation : biodegradation of pollutants by plants, facilitated by microorganisms
in the rhizosphere

This technology is especially valuable where the contaminated soils are fragile and
prone to erosion. Phytotransformation and rhizosphere bioremediation are applicable
to sites contaminated with organic pollutants that include pesticides. It is cost-effective
and has aesthetic advantages and long-term applicability (Brown 1995 ). Plants can
withstand relatively high concentrations of organic chemicals without toxic
effects, and they can uptake and convert chemicals quickly to less toxic metabolites
in some cases. In addition, they stimulate the degradation of organic chemicals in the