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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 systemsType of contaminantGeological 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

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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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