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Bioreactors for bioremediation.

  2. 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.
  3. 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.
  4. BIOREACTOR DESIGN: DEPENDS ON: Contaminant type: soil, sludge, water Cost. Oxygen transfer. Mixing. TWO MAJOR SOIL BIOREACTORS: Dry bioreactors. Slurry bioreactors.
  5. 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.
  6. Negative point: Frequently results in soil/microbe pellet formation
  7. 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).
  8. 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.
  9. 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.
  10. 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.)
  11. 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
  12. 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.
  13. 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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