Bio remediation

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Bio-remediation
wstafford_at_uwc.ac.za
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Bioremediation

• The quality of life on Earth is linked
  inextricably to the overall quality of the
  environment
• The contamination of soil and water with organic
  and inorganic pollutants is of increasing concern
  and the subject of legislation. These pollutants
  include complex organic compounds, heavy metals,
  and natural products such as oils and are derived
  from industrial processing, deliberate release,
  and accidental release. Bioremediation is
  defined as the process whereby organic wastes are
  biologically degraded under controlled conditions
  to an innocuous state, or to levels below
  concentration limits established by regulatory
  authorities.

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• Bioremediation uses naturally occurring bacteria
  and fungi or plants to degrade or detoxify
  substances hazardous to human health and/or the
  environment.
• The microorganisms may be indigenous to a
  contaminated area and stimulated in activity
  (biostimulation) or they may be isolated from
  elsewhere and brought to the contaminated site
  (bioaugmentation).

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• In many cases the clean-up of contaminated sites
  has been carried out using physical and chemical
  methods such as immobilization, removal (dig and
  dump), thermal, and solvent treatments.
• Bioremediation is cheaper than the chemical and
  physical options, and can deal with lower
  concentrations of contaminants more effectively,
  although the process may take longer.
• The strategies for bioremediation in both soil
  and water can be as follows.
• Use the indigenous microbial population.
• Encourage the indigenous population.
• Bioaugmentation the addition of adapted or
  designed inoculants.
• Addition of genetically modified
  micro-organisms.
• Phytoremediation.

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• Many thousands of synthetic organic (xenobiotic)
  compounds have been produced and many of these
  have found their way into the environment. Some
  of the most commonly found are the pesticides
  (biocides), herbicides, and preservatives and
  some of their structures are given in Fig. 5.2.
  Most biocides and herbicides are released into
  the environment by direct use although some may
  be released during manufacture, and spills do
  occur. The scale of herbicide production can be
  seen in Table 5.2, where the herbicide atrazine
  is produced at a rate of 39 000 tonnes per year.
  Other synthetic compounds such as
  poly-chlorobiphenyls (PCBs) are used in hydraulic
  fluids, plasticizers, adhesives, and lubricants
  flame retardants and dielectric fluids in
  transformers are released during production, from
  spillage and disposal. Another group of
  contaminants found frequently in the environment
  are chlorinated compounds such as
  trichloroethene, carbon tetrachloride, and
  pentachlorophenol, which are used as solvents and
  for wood treatment. Other contaminants such as
  dioxins and dibenzofurans can be formed during
  the combustion of polyaro-matic hydrocarbons
  (PAHs) and when heating plant oils. So, depending
  on the properties, such as solubility and the
  nature of their release, these contaminants can
  be localized or widespread.
• Many of the xenobiotic compounds released into
  the environment accumulate because they are only
  degraded very slowly and in some cases so slowly
  as to render them effectively permanent. The
  half-lives (the time required to remove half of
  the compound present) of some of the halogenated
  pesticides

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Xenobiotic persistance
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Recalcitrant chlorinated hydrocarbons
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Agent orange (2,4-D and 2,4-T)

• The effect of the addition of another chlorine to
  2,4-dichlorophenoxyacetic acid (2,4-D), a
  biodegradable compound, forming
  2,4,5-trichlorophenoxyacetic acid (2,4,5-T),
  which is recalcitrant. A mixture of 2,4-D and
  2,4,5-T is known as Agent Orange, and its
  persistence was of great concern when it was used
  as a defoliant in the Vietnam War.
• Caused long-term metabolic and neuroligical
  effects in exposed humans

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Oil spills

• As a result of the petroleum industry millions of
  tons of these compounds enter the oceans every
  year. Many hydrocarbons dissolve slowly in water.
  Others such as the aromatic compounds like
  benzene are more soluble, and these are toxic to
  living cells.
• While accidental releases may contribute to only
  a small percentage of the oil released into the
  marine environment large accidental oil spills
  receive much attention and evoke considerable
  public concern because they can result in
  contamination of ocean and shoreline environments.

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oil spill!

• The biggest spill ever occurred during the 1991
  Persian Gulf war when about 240 million gallons
  spilled from oil terminals and tankers off the
  coast of Saudi Arabia. The Exxon Valdez accident
  at Bligh Reef in 1989 discharged 40 million
  litres.

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Bioremediation to the rescue?..

• Initial studies sowed that the number of oil
  degrading microorganisms on oiled beaches in
  comparison with untreated controls increased by
  as much as 10,000 times
• The biodegradation by indigenous microorganisms
  was monitored by GC-MS, showed that that the
  microbial population could rapidly biodegrade the
  aliphatic and aromatic fractions of crude oil.
  The microbial community decomposed
  dibenzothiphene, fluorenes, naphthalenes,
  phenanthrene, and anthracene completely
  mineralized to CO2 and H2O.
• Data also sowed that nitrate addition stimulated
  biodegradation. Small scale in situ trials with
  Inipol EAP 22- an oleophilic microemulsion
  containing a solution of urea in brine,
  encapsulated in oleic acid and lauryl phosphate..

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Initial experiments revealed visible improvements
after 10 days.

• More extensive beach plot experiments tested
  different nutrient additions and an ecological
  monitoring program was established (U.S. Congress
  1989).
• Results showed that no detectable nutrients ended
  up in the waters off the test site and there was
  no evidence of eutrophication.
• The potential benefits of reducing wildlife
  exposure to oil allowed the EPA to support a
  proposal for application of nutrients to oil
  covered beaches (EPA 1989). By the end of the
  summer of 1989, 100 km of shoreline were treated
  with nutrient applications.
• The results of all tests showed that
  biodegradation can be enhanced about two to three
  fold. This means that an oil spill that would
  take five to ten years to degrade can be degraded
  in as little as two to five years. This
  acceleration of clean-up time, could give
  bioremediation technology a bright future.

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Biodegradable plastics?

• The use of long-lasting polymers for short-lived
  applications is not entirely justified,
  especially when increased concern exists about
  the preservation of living systems.
• Most of today's plastics and synthetic polymers
  are produced from petrochemicals. As conventional
  plastics are persistent in the environment,
  improperly disposed plastic materials are a
  significant source of environmental pollution,
  potentially harming wildlife. (eg 1 in 30
  cetacean carcasses had choked on plastic debris).
  Plastics are also a costly in municipal waste
  management.
• Pertochemical plastics take hundreds of years to
  break down

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but the time for biodegradable plastic to be
composted is 1 to 6 months

• Photobiodegradable plastics.
• Polymers that change structure when illuminated
  with UV radiation, forming biodegradable
  materials.
• Starch-linked biodegradable plastics.
• Starch has been incorporated into the structure
  of some plastics, that can be microbially
  degraded.
• Bacterial plastics.
• A number of microbes naturally produce
  biodegradable polymers that are suitable for the
  plastics industry. For example, the bacterium
  Alcaligenes eutrophus produces the polyester
  poly-beta-hydroxybutyrate (PHB) as a storage
  reserve for excess carbon. The monomeric unit of
  PHB is beta-hydroxybutyrate.
• The strength, flexibility and crystallanity of
  polymers is determined by the Type of repeating
  units and the media and type of bacteria used to
  produce the polymer.

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Why isn't PHB filling up our supermarket shelves?

• A major factor limiting PHB's use is its
  brittleness. But is used in the US navy (cups)
  and Japan (disposable razors!)
• GMO plants producing plastic?
• A team at the DoE Plant research lab at Michigan
  State University took two genes from PHB-making
  bacteria and inserted them cress plants. They had
  managed to create a transgenic plant that could
  grow plastic.
• But scientists really are not yet sure about how
  easy it is to confine genetically modified plants
  in one area, or about the impact so much PHB
  would have on the environment. It's too early yet
  to risk growing PHB on a large scale outdoors?