BIOREMEDIATION
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INTRODUCTION
• Bioremediation is defined as the use of biological treatment
systems to destroy or reduce the concentration of hazardous
wastes from contaminated sites.
• Economical, safety
• Cost-effective, permanent solution to clean up soils
contaminated with xenobiotic compounds
• At least six times cheaper than incineration and three times
cheaper than confinement
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Introduction
• New and exciting field
• Performed off-site when contamination is superficial, but it
will have to be in situ when the contaminants have reached
the saturated zone
• General components and characteristics
Microbial systems
Type of contaminant
Geological and chemical conditions at the contaminated site
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Advantages
• Can be done on site
• Minimum site disruption is caused
• Eliminates transportation costs and liabilities
• Eliminates long-term liabilities
• Uses biological system, often less expensive
• Can be coupled with other treatment techniques
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Disadvantages
• Some chemical compounds are not biodegradable
• Extensive monitoring required
• Each site has specific requirements
• Potential production of toxic unknown sub-products is
possible
• Strong scientific support is needed
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BIOREMEDIATION
TECHNIQUES
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Bioremediation techniques
• Divided into 3 categories :
In-situ, ex-situ and ex-situ slurry
• In situ - soil and associated ground water is treated in place
without excavation
• Ex situ – excavated prior to treatment
• Ex situ slurry – creation and maintenance of soil- water
slurry as bioremediation medium
• Slurry can be maintained either in a bioreactor or in a pond
lagoon 8

In situ remediation
techniques
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In situ remediation techniques
• Bioremediation on land
• Land farming
• Bioventing
• Biosparging
• Bioaugmentation
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Bioremediation on land
• Depend on the area contaminated, the properties of the
compounds involved, the conc of contaminants, time required
to complete the bioremediation
• The contamination can be treated on site or the contaminated
material excavated and treated on or off site.
• If contaminant is water soluble a pump-and-treat technique
used
• Introduced into contaminated areas and removed at another
site to be treated on or off site
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Land farming
• The simplest of the on-site treatment
• Involve mixing of the soil by ploughing or some form of
mechanical tilling
• Ploughing increases the O₂ levels in the soil and distributes
contaminants more evenly, which increases the rate of
degradation.
• Nutrients added to increase biodegradation
• 4-6 months required to remove contaminants such as PAHs
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Land farming
• Method is best suited for shallow contamination of soil
surface
• Treatment area is lined and dammed to retain any
contaminated leachate
• Rate of degradation depends on the microbial pollution, the
type and level of contamination, and the soil type
• Avg half-life for the degeneration of diesel fuel and heavy oils
is in the order of 54 days with this type of system
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Land farming
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Bioventing
• In situ process, which combines an increased oxygen supply
with vapour extraction
• A vacuum is applied at some depth in the contaminated soil
• This draws air down into the soil from holes drilled around
the site and sweeps out any volatile organic compounds
• Nutrient supplementation can be provided by running
nutrients into trenches dug across the site
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Bioventing
• The increased supply of air will increase the rate of natural
degradation by the aerobic micro-organisms.
• Only effective for reasonably volatile compounds, where soil is
permeable
• Vapour extracted may need some form of treatment
• One biological solution is the use of biofilters
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Biosparging
• Process to increase the biological activity of the soil by
increasing the supply of oxygen by sparging air or oxygen
into the soil
• Air injection replaced by pure oxygen – increase degradation
rates
• The expense of treatment limited its application to highly
contaminated sites but on-site degradation of oxygen has
reduced costs
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Biosparging
• Hydrogen peroxide used on a number of sites but it can be
toxic at low concentrations to MO
• This process is similar to soil vapor extraction, which can be
used for volatile contaminants
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Bioaugmentation
• The addition of nutrients injected into contamination well
below the surface can be used to stimulate the indigeneous
microbial population.
• This technique can be combined with the addition of specific
MO
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Ex situ remediation
techniques
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Ex situ remediation techniques
• If the contaminated material is excavated it can be treated on
or off site, which is often a more rapid method of de-
contaminating the area
• The techniques include
– Composting
– Biopile process
– Bioreactors
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Composting
• Solid-phase treatment carried out after extraction
• Composting materials such as straw, bark and wood chips is
mixed with the contaminated soil and piled into heaps
• Process work in the same way as normal system which rise the
temp to 60° C and above cause microbial activity
• higher temp encourages the growth of thermophilic bacteria
• Increased costs of this type of system restrict it to highly
contaminated materials
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Composting
• Organic materials added vegetables, fruit and garden waste
• Added at a conc of 33-75%
• Temp above 70° C achieved after 6-22 days of incubation,
with turning every 7 days and 84-86% of the contamination
was removed by day 40 compared with 35% in untreated soil.
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Biopile process
• Soil heaped into piles within a lined area to prevent leaching
• Piles covered with polythene and liquid nutrients applied to
the surface
• Aeration improved by applying suction to the base of the pile
as in a composting system
• Leachate collected by pipes at the base and recycled if
necessary
• Space limited
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Biopile process
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Bioreactors
• Soil extracted from a contaminated site can be treated as a
solid waste or a liquid leachate in bioreactors of various
designs.
• Control of parameters such as temp, pH, mixing and O₂
supply – improve degradation rates
• Used for Solid waste slurries can be solid-bed, fluidized bed,
and stirred tank bioreactors
• When treating liquid leachates and contaminated ground
water all those reactors – waste water treatment are used
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Bioreactors
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