In Situ Bioremediation;Types, Advantages and limitations

1. Zohaib HUSSAIN
In Situ Bioremediation

2. Bioremediation
• Bioremediation is the use of microorganisms
(e.g., bacteria, fungi), plants (termed
phytoremediation), or biological enzymes to
achieve treatment of hazardous waste.
Treatment can target a variety of media
(wastewater, groundwater, soil/sludge, gas)
with several possible objectives (e.g.,
mineralization of organic compounds,
immobilization of contaminants).
•

3. In Situ Bioremediation
• In situ bioremediation (ISB) is the application
of bioremediation in the subsurface – as
compared to ex situ bioremediation, which
applies to media readily accessible
aboveground (e.g., in treatment cells / soil piles
or bioreactors).
• In situ bioremediation may be applied in the
unsaturated/ vadoze zone (e.g., bioventing) or
in saturated soils and groundwater (Sharma S.
2012).

4. Types of Bioremediation
• Few people realize that in situ
bioremediation is not really a "new''
technology.
• The first in situ bioremediation system was
installed 20 years ago to clean up an oil
pipeline spill in Pennsylvania, and since
then bioremediation has become well
developed as a means of cleaning up easily
degraded petroleum products.

5. Intrinsic Bioremediation
• Intrinsic bioremediation is an option when the
naturally occurring rate of contaminant
biodegradation is faster than the rate of
contaminant migration. These relative rates
depend on the type and concentration of
contaminant, the microbial community, and
the subsurface hydro geochemical conditions.
• The ability of native microbes to metabolize
the contaminant must be demonstrated either
in field tests or in laboratory tests performed
on site-specific samples..

6. • In intrinsic bioremediation the rate-
controlling step is frequently the influx of
oxygen
• Lack of a sufficiently large microbial
population can also limit the cleanup rate.
• The microbial population may be small
because of a lack of nutrients,
• an inhibitory condition such as low PH and
presence of a toxic material.

7. Engineered bioremediation
• Engineered bioremediation may be chosen over intrinsic
bioremediation because of time and liability. Where an
impending property transfer or potential impact of
contamination on the local community dictates the need
for rapid pollutant removal, engineered bioremediation
may be a more appropriate remedy than intrinsic
bioremediation.
• Because engineered bioremediation accelerates
biodegradation reaction rates, it requires less time than
intrinsic bioremediation. The shorter time requirements
reduce the liability for costs required to maintain and
monitor the site. Since many petroleum hydrocarbons
require oxygen for their degradation, the technological
emphasis of engineered bioremediation systems in use
today has been placed on oxygen supply.

8. • Bioremediation systems for soil above the
water table usually consist of a set of vacuum
pumps to supply air (containing oxygen) and
infiltration galleries, trenches, or dry wells to
supply moisture (and sometimes specific
nutrients).
• Bioremediation systems for ground water and
soil below the water table usually consist of
either a set of injection and recovery wells used
to circulate oxygen and nutrients dissolved in
water or a set of compressors for injecting air.

9. • Emerging applications of engineered
bioremediation, such as for degradation of
chlorinated solvents, will not necessarily be
controlled by oxygen. Hence, the supply of
other stimulatory materials may require
new technological approaches even though
the ultimate goal, high biodegradation rates,
remains the same.

10. Measurements of Field Samples
• The following techniques for documenting in situ
bioremediation involve analyzing the chemical and
microbiological properties of soil and ground water samples
from the contaminated site.
• Number of bacteria Because microbes often reproduce when they
degrade contaminants, an increase in the number of contaminant-
degrading bacteria over usual conditions may indicate successful
bioremediation.
• Number of protozoans, Because protozoans prey on bacteria, an
increase in the number of protozoans signals bacterial population
growth, indicating that bioremediation may be occurring. Rates of
bacterial activity. Tests indicating that bacteria from the
contaminated site degrade the contaminant rapidly enough to effect
remediation when incubated in microcosms that resemble the field
site provide further evidence of successful bioremediation.
• Adaptation. Tests showing that bacteria from the bioremediation
zone can metabolize the contaminant, while bacteria from outside
the zone cannot (or do so more slowly), show that the bacteria have
adapted to the contaminant and indicate that bioremediation may
have commenced.

11. • Carbon isotopes. Isotopic ratios of the inorganic carbon (carbon
dioxide, carbonate ion, and related compounds) from a soil or water
sample showing that the contaminant has been transformed to
inorganic carbon are a strong indicator of successful bioremediation.
• Metabolic byproducts. Tests showing an increase in the
concentrations of known byproducts of microbial activity, such as
carbon dioxide, provide a sign of bioremediation. Intermediary
metabolites. The presence of metabolic intermediates simpler but
incompletely degraded forms of the contaminant in samples of soil
or water signals the occurrence of biodegradation.
• Growth-stimulating materials. A depletion in the concentration of
growth-stimulating materials, such as oxygen, is a sign that
microbes are active and may indicate bioremediation.
• Ratio of non degradable to degradable compounds. An increase
in the ratio of compounds that are difficult to degrade to those that
are easily degraded indicates that bioremediation may be occurring.

12. Advantages of In Situ Bioremediation
• Transformation organic contaminants to innocuous substances
(e.g., carbon dioxide, water, ethane).
• Accelerated ISB can provide volumetric treatment, treating both
dissolved and absorbed contaminant.
• Time to accelerated in situ bioremediation can often be faster
than pump and-treat processes.
• Less costs than other remedial options.
• The areal zone of treatment using bioremediation can be larger
than with other remedial technologies As an in situ (versus ex
situ) technology, there is typically little secondary waste
generated
• As an in situ (versus ex situ) technology, there is reduced
potential for cross-media transfer of contaminants
• As an in situ (versus ex situ) technology, there is reduced risk of
human exposure to contaminated media.

13. Limitations of In Situ Bioremediation
• Some contaminants may not be completely transformed to innocuous
products.
• The intermediate produce may be more toxic and/or mobile than the
parent compound.
• Some contaminants cannot be biodegraded (i.e., they are recalcitrant).
• Coagulation
• Difficult to implement completely in low-permeability or heterogeneous
aquifers.
• Heavy metals and toxic concentrations of organic compounds may inhibit
activity of indigenous microorganisms.
• Microbe not develop for recent spills or for recalcitrant compounds.

14. Refrences
• http://bioprocess.pnnl.gov/resour/rt3d.in.situ.bi
oremediation.htm
• In situ bioremediation when does it work?
(1993). Washington, D.C.: National Academy
Press.
• Sharma, S. (2012). Bioremediation: features,
strategies and applications. Asian Journal of
Pharmacy and Life Science ISSN, 2231, 4423.
• Alexander, M. (1999). Biodegradation and
bioremediation. Gulf Professional Publishing.