Use of biotechnology for toxic site reclamation
Generally incineration (drying and then burning to ashes in furnace) or chemical treatment are being used to get rid of toxins and waste from the waste disposal sites. Of late, biotechnological techniques involving biodegradation as an alternative approach is being used. Companies like BioTechnica are working on treating polluted site in situ. However there is a lot of debate over the issue regarding the release of genetically engineered microbes for treatment of toxic sites and the risk involved in the whole procedure. As we know that the released engineered organisms have the capacity to reproduce, spread to sites other then the initial release sites and may undergo mutations. All this can lead to the risk of developing what are described as “super bugs”. Some of the companies in US are experimenting and conducting their work in the closed reactors in order to further evaluate the risk assessment and cost effectiveness of this approach.
In order to solve the problem of soil pollution caused due to extensive use of herbicides, pesticides and insecticides, the bioremediation of soil using microorganisms is being carried out. The most common pollutants are: hydrocarbons, chlorinated, solvents, polychlorobiphenyls and metals. The bioremediation of soil involves two processes:
In order to solve the problem of soil pollution caused due to extensive use of herbicides, pesticides and insecticides, the bioremediation of soil using microorganisms is being carried out. The most common pollutants are: hydrocarbons, chlorinated, solvents, polychlorobiphenyls and metals. The bioremediation of soil involves two processes:
a) Biostimulation- Biostimulation involves the stimulaton of microorganisms already present in the soil. This can be done by adding nutrients e.g. nitrogen, phosphorus etc., by supplying co-substrates e.g. methane which can degrade trichloroethylene, or by adding surfactants to disperse the hydrophobic compounds in water.
b) Bioaugmentation- Addition of specific microorganisms to the polluted soil constitutes bioaugmentation. Some of the pollutants like polychlorobiphenyls (PCBs), trinitrotoluene (TNT), polyaromatic hydrocarbons (PAHs) etc are not degraded by only native soil microorganisms so a combination of microorganisms referred to as “consortium” or “cocktail” of microorganisms is added to achieve bioaugmentation.
c) Bioventing- Bioventing involves aerobic biodegradation of pollutants by circulating air through sub-surfaces of soil and is one of the very cost effective and efficient technique used for the bioremediation of petroleum contaminated soils. It is very effectively used for degradation of soluble paraffins, and polyaromatic hydrocarbons.
d) Phytoremediation- Bioremediation by using plants is called phytoremediation. Certain plant species which have the capability to stimulate biodegradation of pollutants (specially near the soil adjacent to roots- rhizophere) are cultivated near the sites of polluted soil. This is a cheap and environmentally friendly process but takes a long time to finish the clean up process.
e) Land farming- Landfarming is a technique for the bioremediation of hydrocarbon contaminated soils. In this the soil is excavated, mixed with microorganisms and nutrients and spread out on a liner just below the polluted soil.
f) Use of slurry-phase bioreactors- In this process, the excavated polluted soil is subjected to bioremediation under optimal controlled conditions in specifically designed bioreactors.
Table showing engineered bacteria used for the degradation of xenobiotics and toxic wastes
| Bacterium |
Substrate that can be degraded |
| Pseudomonas capacia |
2,4,5- trichoro-phenoxyacetic acid |
| P. putida & other spp (also E.Coli) |
2,2,5-dichloropropionate; mono and dichloroaromatics |
| Alcaligenes sp. |
Dichlorophenoxyacetic acid, mixed chlorophenols; 1,4- dichlorobenzene |
| Acinetobacter sp. |
4-chlorobenzene |
| Bacterium |
Substrate that can be degraded |
| Pseudomonas capacia |
2,4,5- trichoro-phenoxyacetic acid` |
| P. putida & other spp (also E.Coli) |
2,2,5-dichloropropionate; mono and dichloroaromatics |
| Alcaligenes sp. |
Dichlorophenoxyacetic acid, mixed chlorophenols; 1,4- dichlorobenzene |
| Acinetobacter sp. |
4-chlorobenzene |
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