Bioremediation

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Bioremediation

• Chapter 8

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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

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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

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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?

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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

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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?

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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

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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

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What Makes Bioremediation a Promising Approach?

• permanence
• contaminant is degraded
• potentially low cost
• 60-90 less than other technologies

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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.

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Contaminants Potentially Amenable to
Bioremediation___________________________________
_________
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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

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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

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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
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Uranium reduction leads to uranium precipitation
and immobilization
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Volatile organic compounds (VOC)

• These are major contributors to air pollution
• Paint industry
• Pharmaceutical industry
• bakeries
• printers
• dry cleaners
• auto body shops

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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
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Hard to degrade contaminants

• Chlorinated hydrocarbons
• solvents
• lubricants
• plasticizers
• insulators
• herbicides and pesticides.

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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.

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CO2 H2O

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

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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
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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)
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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

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Phytoremediation

• Drawbacks
• Only surface soil (root zone) can be treated
• Cleanup takes several years

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Transgenic plants
Royal Demolition eXplosive
Gene from bacterium moved to plant genome
Stimulates plant growth!
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Careers in Bioremediation

• Outdoor inspection
• Lab testing
• Administration

Government Employee Regulatory oversight
Company employee
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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