The term "bioreactor" in the context of
soil and water bioremediation refers to
any vessel or container where biological
degradation of contaminants is isolated
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.
Contaminant type: soil, sludge, water
TWO MAJOR SOIL BIOREACTORS:
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.
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
ADVANTAGES AND DISADVANTAGES
Relatively rapid treatment.
Reduced pellet formation.
Increased slurry homogenization.
Soil-water separation can become a problem (Nyer, 1993).
Also, there is a need for wastewater treatment after the soil
BIOREACTORS FOR GROUNDWATER:
Usually fixed film or some form of activated
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
AEROBIC AND ANAEROBIC PROCESSES
Bioreactors can also be designed to operate aerobic and anaerobic
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.)
Workhorses of the bioremediation process.
The microorganisms responsible for pollutant
degradation are usually bacteria but can also be
Microbes usually need not be added to the soil in a
bioreactor since they are usually present in
The exception being when a toxic substance has
removed all endemic microorganisms
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.
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.