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Bioremediation for Sustainable Environmental Cleanup

diffusion of volatile pollutants through open stomata of the leaves in a less toxic form. This involves

the removal of the pollutants in a gaseous form and the particular pollutant removal in safer forms.

1.6.1.3 Phytostabilization

Phytostabilization is a process in which the stabilization or fixation of heavy metals occurs so that

proper absorption and precipitation take place mainly through the soil, sediment and sludge (USEPA

2000). In this process, contaminants are absorbed and collected by roots or precipitate inside the root

zone of plants (rhizosphere).

1.6.1.4 Phytofiltration/Rhizofiltration

Precipitation and absorption by plants from soil and water are the main mechanisms in rhizofiltration.

In this process, the contaminants are restricted only to the root system. Various heavy metals are

retained by the root system in rhizofiltration (USEPA 2000). In rhizofiltration, plant roots grow very

rapidly and require minimal time for decontamination (Sarkar et al. 2011).

1.6.1.5 Phytotransformation

Phytotransformation, also known as phytodegradation is the breakdown of organic pollutants

sequestered by plants through (1) metabolic processes inside the plant; or (2) the influence of

substances produced by the plant, such as enzymes (EPA 1998). It contributes to the removal of

organic pollutants such as chlorinated solvents, herbicides and the breakdown of complex organic

compounds into simple ones (EPA 2000). As plants do not contain active transporters, these organic

contaminants are absorbed through passive uptake. When the degradation of contaminants occurs in

the rhizosphere, the process is called rhizodegradation. Organics such as polyaromatic hydrocarbons

and polychlorinated biphenyls can be mineralized by rhizospheric bacteria. Furthermore, enzymatic

breakdown by enzymes released by specific plants and associated microbe species, such as

dehalogenase, nitro-reductase, laccase peroxidase and others, acts on dangerous xenobiotics

(Cherian and Oliveira 2005).

1.6.2 Advantages and Disadvantages of Bioremediation

Bioremediation is the best option over conventional methods for remediation such as incineration,

landfilling, etc. Bioremediation can be done on-site, thereby reducing expenses and risks associated

with transportation, can treat or eliminate a wide range of diffused contaminants permanently,

and can be applied to large-scale operations (Van Aken 2009). Other advantages include being

environmentally friendly, affordable due to its minimal installation and a higher level of public

acceptance (Ali and Sajad 2013). Advantages of phytoremediation include the development of soil

fertility, recovery of valuable metals and avoidance of metal erosion and leaching (Mench et al.

2009).

Several disadvantages also exist with the bioremediation technique. The use of bioremediation

is restricted to biodegradable substances only. Substances like metals, chlorinated organic pollutants

and radionuclides are not capable of complete and quick degradation. Sometimes, the by-products

of biodegradation may be more toxic and persistent during the metabolism of contaminants. Some

drawbacks of the phytoremediation technique include longer treatment time, higher pollutant

concentrations and bioavailability to plants, the toxicity of pollutants to plants and the inability to

treat organic contaminants due to the lack of enzymes for their degradation (Ali et al. 2013).

1.7 Conclusion

In the chapter, a brief account of the principle, types, applications, benefits and drawbacks of

bioremediation techniques have been discussed. As a result, one can see that compared to other

physical and chemical remediation approaches, it is an emerging, interdisciplinary, effective and

environmentally friendly remediation approach that is currently paving the way to a more promising