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Bio remediation


The contamination of soil and water with organic and inorganic pollutants is of ... ( eg 1 in 30 cetacean carcasses had choked on plastic debris) ... – PowerPoint PPT presentation

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Title: Bio remediation

  • The quality of life on Earth is linked
    inextricably to the overall quality of the
  • 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

  • Bioremediation uses naturally occurring bacteria
    and fungi or plants to degrade or detoxify
    substances hazardous to human health and/or the
  • 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

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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
  • 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

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Xenobiotic persistance
Recalcitrant chlorinated hydrocarbons
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

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.

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

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..

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
  • 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.

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
  • Pertochemical plastics take hundreds of years to
    break down

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
  • Starch-linked biodegradable plastics.
  • Starch has been incorporated into the structure
    of some plastics, that can be microbially
  • 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.

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?
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