bioreactors for bioremediation

BIOREACTORSPRESENTED BY: SUMBAL

DEFINITION:

The term "bioreactor" in the context of soil and water bioremediation refers to any vessel or container where biological degradation of contaminants is isolated and controlled.

BIOREACTOR:Range from: crude devices such as lined

depressions in the ground to advanced metal

containers where environmental conditions

can be monitored and controlled.

Treatment mechanism: in a bioreactor is

natural degradation by existing and/or added

populations of microorganisms

Effective in: remediating soil, and in some

cases water, polluted with fuel hydrocarbons

(oil, gasoline, diesel) and organics.

BIOREACTOR DESIGN:

DEPENDS ON:

Contaminant type: soil, sludge, water

Cost.

Oxygen transfer.

Mixing.

TWO MAJOR SOIL BIOREACTORS:

Dry bioreactors.

Slurry bioreactors.

DRY BIOREACTOR:

Treat soil with no other amendments other than microbes and nutrients.

Adequate moisture is maintained for microbial growth by sprinkler system or by rainfall.

Physical mixing of the soil keeps it aerated.

After the remediation process is complete the soil can be transported to a desired location.

Negative point:Frequently results in soil/microbe pellet formation

SLURRY BIOREACTORS

Proven more effective and efficient against a wider range of pollutants.

In a slurry reactor the soil is mixed with equal or greater amounts of water and mixed with microbes and nutrients to form a soil slurry.

Conditions in a slurry reactor are easier to maintain than dry reactors and result in faster treatment rates.(Nyer, 1993).

ADVANTAGES AND DISADVANTAGES

ADVANTAGES:

Relatively rapid treatment.

Reduced pellet formation.

Increased slurry homogenization.

Increased bioavailability.

DISADVANTAGES:

Soil-water separation can become a problem (Nyer, 1993).

Also, there is a need for wastewater treatment after the soil is dewatered.

BIOREACTORS FOR GROUNDWATER:

Usually fixed film or some form of activated sludge reactors.

Fixed film reactors contain high surface area media that support microbial growth.

Activated sludge reactors are aerated basins where microbes are mixed with the wastewater and nutrients.

AEROBIC AND ANAEROBIC PROCESSES

Bioreactors can also be designed to operate aerobic and anaerobic processes.

Anaerobic degadation reduce highly halogenated compounds such as trichloroethylene to less halogenated compounds.

Aerobic degradation pathways:

effective against a wider range of pollutants

most widely implemented processes.

Use of anaerobic and aerobic steps in series offers a method to treat substances that do not respond to conventional treatment.

(An example is highly chlorinated organic pollutants. Anaerobic organisms can dechlorinate the substance to a point where aerobic organisms can completely degrade it.)

Microorganisms

Workhorses of the bioremediation process.

The microorganisms responsible for pollutant degradation are usually bacteria but can also be fungi.

Microbes usually need not be added to the soil in a bioreactor since they are usually present in adequate amounts.

The exception being when a toxic substance has removed all endemic microorganisms

Electron acceptor:

Require a supply of nutrients and an electron acceptor.

Aerobic organisms use oxygen as the final electron acceptor and organic carbon as a carbon source.

Anaerobic organisms use sulfate or carbon dioxide as the electron acceptor.

Facultative organisms: utilize nitrates, iron, and manganese as electron acceptors.

NUTRIENTS:

Main nutrients: Nitrogen and phosphorous

A general rule of thumb for N and P loading is five parts nitrogen and one part phosphorus.

Micronutrients such as Ca, Fe, Mg, Mb, and S are usually present in sufficient amounts in the soil to adequately supply microbe metabolism.

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