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Bioremediation. Chapter 8. What is bioremediation?. The use of bacteria and fungi and plants to break down or degrade toxic chemical compounds that have accumulated in the environment. Pollutants

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what is bioremediation

What is bioremediation?

The use of bacteria and fungi and plants to break down or degrade toxic chemical compounds that have accumulated in the environment

what are environmental contaminants
Pollutants

naturally-occurring compounds in the environment that are present in unnaturally high concentrations.

Examples:

crude oil

refined oil

phosphates

heavy metals

Xenobiotics

chemically synthesized compounds that have never occurred in nature.

Examples:

pesticides

herbicides

plastics

What are environmental contaminants?
early examples of bioremediation
Early examples of bioremediation
  • Outhouse→Centralized engineered wastewater treatment systems
    • Microorganisms oxidize organic waste molecules to carbon dioxide and water
    • Why do we want to use engineered man-made for this?
more recent examples
More recent examples
  • By 1970s it became apparent that we were polluting the environment faster than the natural microbial processes could degrade the pollutants
    • Congress established the Environmental Protection Agency
      • Identified “Superfund Sites” that had priority over other polluted systems for special funding and cleanup in 1980
        • 1 in 5 Americans lives within 3-4 miles of a polluted site treated by the EPA
        • Not much progress has been made even though $billions has been spent
groundwater contamination
Groundwater contamination
  • Groundwater constitutes 96% of available freshwater in U.S.
  • 95% of potable water in rural areas of U.S. comes from groundwater
  • In 1988, EPA confirmed that 26 states had various amounts of 44 different pesticides in their groundwater
  • Cost of cleanup is in the $ trillions
  • Issues that are still hotly debated
    • How clean is clean?
most recent
Most recent
  • National Institute of Environmental Health Sciences established the Environmental Genome Project
    • Study impact of environmental chemicals on human disease
      • Identify genes and their products that are sensitive to toxic chemicals in the environment
      • Identify genes that encode for products that detoxify the chemicals
what types of treatment technologies are in use to remove contaminants from the environment
What types of treatment technologies are in use to remove contaminants from the environment?
  • Soil vapor extraction
  • air sparging
  • bioremediation
  • thermal desorption
  • soil washing
  • chemical dehalogenation
  • soil extraction
  • in situ soil flushing
what makes bioremediation a promising approach
What Makes Bioremediation a Promising Approach?
  • permanence
    • contaminant is degraded
  • potentially low cost
    • 60-90% less than other technologies
economics of in situ vs ex situ remediation of contaminated soils
Economics of in-situ vs. ex-situ remediation of contaminated soils
  • Cost of treating contaminated soil in place $80-$100 per ton
  • Cost of excavating and trucking contaminated soil off for incineration is $400 per ton.
  • Over 90% of the chemical substances classified as hazardous today can be biodegraded.
contaminants potentially amenable to bioremediation
Contaminants Potentially Amenable to Bioremediation____________________________________________
what challenges exist for bioremediation of pollutants and xenobiotics
Pollutants

may exist at high, toxic concentrations

degradation may depend on another nutrient that is in limiting supply

Xenobiotics

microbes may not yet have evolved biochemical pathways to degrade compounds

may require a consortium of microbial populations

What challenges exist for bioremediation of pollutants and xenobiotics?
fundamentals of cleanup reactions
Fundamentals of cleanup reactions
  • Aerobic metabolism
    • Microbes use O2 in their metabolism to degrade contaminants
  • Anaerobic metabolism
    • Microbes substitute another chemical for O2 to degrade contaminants
      • Nitrate, iron, sulfate, carbon dioxide, uranium, technicium, perchlorate
slide17

Metabolism of a Pollutant-degrading Bacterium

Fe(III)

ACETATE

*U(VI)

*Co(III)

*Cr(VI)

*Se(VI)

*Pb(II)

*Tc(VII)

*Benzoate

*Toluene

*Phenol

*p-Cresol

*Benzene

ATP

CO2

Fe(II)

*CCl4

*Cl-ethenes

*Cl-aromatics

*Nitro-aromatics

uranium reduction leads to uranium precipitation and immobilization

U6+sol

U4+insol

U6+sol

U6+sol

U4+insol

Uranium reduction leads to uranium precipitation and immobilization
volatile organic compounds voc
Volatile organic compounds (VOC)
  • These are major contributors to air pollution
    • Paint industry
    • Pharmaceutical industry
    • bakeries
    • printers
    • dry cleaners
    • auto body shops
cometabolism
Cometabolism
  • Bacterium uses some other carbon and energy source to partially degrade contaminant (organic aromatic ring compound)

degradation

products

contaminant

bacterium

corn

starch

CO2 + H2O

hard to degrade contaminants
Hard to degrade contaminants
  • Chlorinated hydrocarbons
    • solvents
    • lubricants
    • plasticizers
    • insulators
    • herbicides and pesticides.
degradation of chlorinated hydrocarbons
Degradation of chlorinated hydrocarbons
  • Degradation of organic toxins requires the participation of entire biochemical pathways involving many enzymes coded for by many genes.
  • Some of the genes exist on the chromosome while other genes reside on plasmids.
slide24

CO2 + H2O

  • Phenol-degrading dmp operon is regulated by DmpR, a NtrC-like positive regulator.
slide25

The layout of the genes involved in chlorocatechol-degradation on the plasmid is similar to the layout of the catechol-degrading genes on the chromosome

genetic engineering of bacteria to remove toxic metals from the environment
Genetic engineering of bacteria to remove toxic metals from the environment

E. coli bacterium

New gene/transport proteins

Hg2+-metallothein

Hg2+→Hgo

Hg2+

New gene/enzyme

Hgo (less toxic form of metal)

phytoremediation
Phytoremediation
  • ≈350 plant species naturally take up toxic materials
    • Sunflowers used to remove radioactive cesium and strontium from Chrenobyl site
    • Water hyacinths used to remove arsenic from water supplies in Bangladesh, India
phytoremediation1
Phytoremediation
  • Drawbacks
    • Only surface soil (root zone) can be treated
    • Cleanup takes several years
transgenic plants
Transgenic plants

Royal

Demolition

eXplosive

Gene from

bacterium

moved to

plant genome

Stimulates plant growth!

careers in bioremediation
Careers in Bioremediation
  • Outdoor inspection
  • Lab testing
  • Administration

Government

Employee

Regulatory oversight

Company employee

summary
Summary
  • Many factors control biodegradability of a contaminant in the environment
  • Before attempting to employ bioremediation technology, one needs to conduct a thorough characterization of the environment where the contaminant exists, including the microbiology, geochemistry, mineralogy, geophysics, and hydrology of the system