Environmental Engineering Reference
In-Depth Information
hazardous and persistent contaminants in the environment in a cost-effective
way. Bacterial bioremediation is normally an in situ treatment method, meaning
there are no significant transportation requirements, need for heavy equipment,
or expensive cleanup procedures. Since this process is fundamentally natural,
cost is nominal and the process may be able to proceed with a minimum of
human interaction (Chapell 1995). As far as treatment is concerned, basically all
of the uses of bioremediation have the same goal in mind—reduction of some
unwanted contaminant—as well as the same technique in which the bacteria
consume or degrade the contaminant to constituents that can easily be treated
by other means. The types of microbial processes that will be employed in the
cleanup dictate what nutritional supplements the bioremediation system must
supply. The byproducts of microbial processes can provide indicators that the
bioremediation is successful.
There are two types of bioremediation:
1. Intrinsic bioremediation. The native subsurface microbes degrade the con-
taminants without direct human intervention. This does not accelerate the
treatment but prevents spread of further contaminants.
2. Engineered bioremediation. This is the acceleration of microbial activity
using engineered site-modification procedures such as installation of wells
to circulate fluids and nutrients to stimulate microbial growth. Air is often
forced into the ground to supply needed oxygen for the bacteria. The
process can be accelerated by increasing airflow and warming up the
soil temperature using heat wells, which provide better conditions for
microbial activity. The principal objective of engineered bioremediation
is to isolate and control contaminated field sites so that they will become
in situ bioreactors.
Some of the hazardous compounds that can be treated by using bioremedi-
ation are petroleum hydrocarbons and derivatives such as gasoline compounds
(benzene, toluene, ethylbenzene, and xylene), fuel oil, polycyclic aromatic hydro-
carbons (PAHs), creosote, ethers, alcohols, ketones and esters. Others are halo-
genated compounds with halogen atoms (usually chlorine, bromine, or fluorine)
added to them in place of hydrogen atoms and nitro aromatics, which are organic
chemicals, and with the nitro (-NO 2 ) bonded to one or more carbons in a benzene
ring. An example is the chemical used in explosive laboratories trinitrotoluene
(TNT). Although microorganisms cannot destroy metals, they can alter their
reactivity, mobility, and toxicity.
3.8
Phytoremediation
Phytoremediation uses green plants to assist in cleaning up contamination from
soils, groundwater and surface waters. Phytoremediation may be conducted near
surfaces of soils, in situ in the deep aquifer, or ex situ for the treatment of contam-
inated liquids by extracting groundwater or surface water. The plants can excrete
 
 
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