Transcript example redox

Groundwater Pollution
Using the characteristics of living
things as tools for environmental
improvement - exercises & case
studies
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The pollution of groundwater
by organic chemicals affects
300,000 to 400,000
contaminated sites in the US
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Picture: http://commons.wikimedia.org/wiki/Image:Drainage_nitrates_vers_HondeghemFr_2003_04_09.jpg
Bioremediation is when
organisms either
metabolize or fix
contaminants
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Contaminant
Organisms
Less harmful
chemicals
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Contaminant
Organisms
Contaminants
are fixed
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Bioremediation is
any process that
uses
microorganisms,
fungi, green plants
or their enzymes to
return the
contaminated
environment to its
original condition.
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Because there
is too much of
something we
need to either
reduce it or
immobilize
(fix) it
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Other Names
Bioremediation is also called
enhanced (늘리다)
bioremediation or engineered
bioremediation.
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Aerobic bioremediation
usually involves oxidative
processes
Contaminants may be partially
oxidized to less toxic things
Contaminants may be fully
oxidized to chemicals such as
carbon dioxide and water
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BTEX (Benzene, Toluene,
Ethylbenzene, and Xylenes)
are monoaromatic
hydrocarbons which are in
petroleum and petroleum
products such as gasoline.
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If there is enough oxygen more
degradation can happen
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If there is enough oxygen they
can degrade to water and
carbon dioxide
2C6H6 + 15O2
12CO2 + 6H2O
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Energy
Microorganism
CO2 + H2O +
other waste
Products +
Reduced electron
Acceptor (H2O)
Organic pollutant &
Oxidized electron
Acceptor (O2)
Energy
Outputs
Inputs
Boundary
Feedback
Environment
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The organisms make
chemical reactions happen
Balance these reactions
Benzene (a component of gasoline)
2C6H6 + 15O2
?CO2 + ?H2O
Alanine (an amino acid)
4C3H4NH2O2H + 15O2
12CO2 + 14H2O + ?
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The organisms make chemical
reactions happen
Balance these reactions
Benzene (a component of gasoline)
2C6H6 + 15O2
12CO2 + 6H2O
Alanine (an amino acid)
4C3H4NH2O2H + 15O2
12CO2 + 14H2O + 2N2
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These chemical equations are
used to calculate how many
other chemicals need to be
added
150 kg of analine needs to be
degraded.
How much oxygen needs to
be supplied?
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Atomic weights
N=14 O=16 H=1 C=12
C3H4NH2O2H = 89
4C3H4NH2O2H needs 15O2
150 / 89 x 4 = X / 32 x 15
X = 202 kg O2
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Bioremediation might be
improved
We could add
more or better
organisms to the
soil
(bioaugmentation)
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We could help
the organisms
grow by
changing things
in the
environment
(biostimulation)
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How could we stimulate the
growth of microorganisms?
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How could we stimulate the
growth of microorganisms?
We could add nutrients, change the
pH, change the temperature, and
add or remove oxygen.
Eg Benzene
2C6H6 + 15O2
12CO2 + 6H2O
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We can engineer the conditions
Engineered bioremediation
involves supplying oxygen (or
other electron acceptor), water,
and nutrients at the correct rate
so that the naturally existing
microorganisms are stimulated
to degrade the contaminants.
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Microbial biodegradation of pollutants occurs
most rapidly under certain optimal conditions:
Temperature (15-30 C)
High moisture content
High oxygen content
Nutrient availability
Usually neutral pH (~7)
Constant ionic strength
Absence of toxic inhibitors
Biotechnological plants try to maintain optimal
conditions for micro-organisms
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How can we follow what is
happening?
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Signs of Biological Activity
Biological activity will result
in decreased oxygen
concentration (for aerobic
processes) and increased
metabolites (e.g. CO2).
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Contaminant
Organisms
Less harmful
chemicals
We can count this, this or this.
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Types of Contaminants
Bioremediation is commonly used for:
Organic contaminants
Some inorganic pollutants such as
ammonia, nitrate, and perchlorate
Changing the valence states of heavy
metals to convert them into immobile or
less toxic forms. (eg mobile hexavalent
chromium into immobile and less toxic
trivalent chromium)
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Perchlorates are the salts of
perchloric acid (HClO4).
They are commonly found in
rocket fuel and explosives, often
those used by the military.
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Advantages of Bioremediation
It may result in complete degradation of
organic compounds to nontoxic
byproducts.
Not much equipment is needed
Bioremediation does not change the
natural surroundings of the site.
Low cost compared to other remediation
technologies.
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Advantage 우위
Toxic
≠
nontoxic
equipment 설비
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Disadvantages of Bioremediation
There could be partial degradation to
metabolites that are still toxic and/or
more mobile in the environment.
Biodegradation is easily stopped by
toxins and environmental conditions.
We have to always measure
biodegradation rates.
Generally requires longer treatment time
as compared to other remediation
technologies.
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Partial 불완전한
Mobile 가동성의
Rate 속도, 진도
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Bioremediation processes may give:
complete oxidation of organic contaminants
(called mineralization),
biotransformation of organic chemicals into
smaller parts, or
reduction of halo- and nitro- groups by
transferring electrons from an electron
donor (eg a sugar or fatty acid) to the
contaminant, resulting in a less toxic
compound.
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Usually electron acceptors are used
by bacteria in order of their
thermodynamic energy yield :
oxygen,
nitrate,
iron,
sulfate,
carbon dioxide.
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The major nutrients needed
include carbon, hydrogen,
oxygen, nitrogen and
phosphorous.
The amount which needs to be
added depends on what is
already there.
Generally, the C to N to P ratio
(w/w) required is 120:10:1.
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Bioreactors are biochemical-processing
systems designed to degrade
contaminants using microorganisms.
Contaminated water flows into a tank,
where microorganisms grow and
reproduce while degrading the
contaminant.
The biomass produced is then separated
from the treated water and disposed of
as a biosolids waste.
This technology can be used to treat
organic wastes (BOD), ammonia,
chlorinated solvents, propellants, and
fuels.
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Artificial wetland ecosystems
(organic materials, microbial fauna,
and algae) can remove metals,
explosives, and other contaminants
from inflowing water.
The contaminated water flows into
the wetland and is processed by
wetland plants and microorganisms
to break down and remove the
contaminants.
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Constructed wetlands
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Bioremediation
(김동진 교수)
Relies on microorganisms to biologically
degrade groundwater contaminants through a
process called biodegradation.
It may be engineered and accomplished in two
general ways:
(1) stimulating native microorganisms by
adding nutrients, oxygen, or other electron
acceptors (a process called biostimulation); or
(2) providing supplementary pregrown
microorganisms to the contaminated site to
augment naturally occurring microorganisms
(a process called bioaugmentation).
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Bioremediation
(김동진 교수)
It mainly focuses on remediating organic
chemicals such as fuels and chlorinated
solvents.
One approach, aerobic bioremediation,
involves the delivery of oxygen (and
potentially other nutrients) to the aquifer
to help native microorganisms reproduce
and degrade the contaminant.
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Bioremediation
(김동진 교수)
Another approach, anaerobic bioremediation,
circulates electron donor materials—for
example, food-grade carbohydrates such as
edible oils, molasses, lactic acid, and cheese
whey—in the absence of oxygen throughout
the contaminated zone to stimulate
microorganisms to consume the contaminant.
In some cases, pregrown microbes may be
injected into the contaminated area to help
supplement existing microorganisms and
enhance the degradation of the contaminant, a
process known as bioaugmentation.
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Bioremediation can be
used to treat groundwater
and landfills
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Bioremediation
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Bioreactor
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Phytoremediation
Selected vegetation reduces,
removes, and stops the toxicity
of environmental contaminants,
such as metals and chlorinated
solvents.
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What does Phytoremediation do?
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In Situ Phytoremediation System
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Aerobic is often faster than
anaerobic degradation
However, many compounds
can only be metabolized
under reductive conditions.
Then anaerobic metabolism is
needed.
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One type of anaerobic
bioremediation is reductive
dehalogenation where the
contaminants are made less
toxic by removal of halogens
such as chlorine or nitro
groups.
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In the degrading of
tetrachloroethene
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Anaerobic = no oxygen
Tetrachloroethene is reduced with
eH2 is the electron donor
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Energy
Microorganism
Electron donor
(sugar, fatty acid, H2) &
Electron acceptor
(electrophilic pollutant)
Oxidized electron donor
CO2 + H2O and
other fermentation
products +
Less halogenated
pollutant and ClEnergy
Outputs
Inputs
Boundary
Feedback
Environment
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At many contaminated sites,
organisms naturally exist that
can degrade the contaminants
But not all sites have organisms
that work.
Some sites don’t have the right
conditions (such as electron
acceptors) for fast degradation
of the contaminants.
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In methanogenic
bioremediation, the
contaminants are converted
to methane, carbon dioxide
and traces of hydrogen.
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Energetics
In order for energy to be released from
an oxidation/reduction reaction, an
overall negative Gibb’s free energy must
exist.
Different inorganic compounds can be
used as terminal electron acceptors by
bacteria during respiration.
Anaerobic respiration usually gives lower
energy than aerobic.
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Questions
Describe these examples of
bioremediation. Use the system
model. State what the electron
acceptors and donors are.
1. Water from a beef farm has a
high level of organic wastes. It is
treated by aeration.
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2. Some oil is spilt on the
ground
Residual NAPL
Mobile
LNAPL
Pool
Methanogenesis
Aerobic
Respiration
Dentrification
Sulfate
Reduction
Iron (III) Reduction
Ground
Water
Flow
Plume of
Dissolved Fuel
Hydrocarbons
(Source: W,R, N, & W, 1999.)
(Adapted from Lovley et al., 1994b.)
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3. Dissolved oxygen depletion
(From: Environmental Science: A Global Concern, 3rd ed. by W.P
Cunningham and B.W. Saigo, WC Brown Publishers, © 1995)
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4. Breaking aromatic rings
From: Atlas and Bartha, 1998
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General Metabolic Redox Model in Microorganisms
Terminal e- Acceptor
Organic Carbon
Oxidation to yield
energy; can be multiple
steps
Oxidized Product
e-
Reduction to
provide e- “sink”
(costs energy)
Reduced Product
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General Model for Aerobic Respiration
O2
Organic Carbon
Energy
production;
multiple steps
CO2
e-
Aerobic
respiration
H2O
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Aerobic Respiration: Examples and Cometabolism
TCE
No energy
production;
cometabolism
CO2
Benzene
Energy
production
CO2
O2
CH4
Energy
production
CH3OH
e-
Coupled
reduction
H2O
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