Groundwater Polllution
150604 GW 15 Biodegradation
Bioremediation
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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
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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 plants reduce, remove, and
stop 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 e-
H2 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
Mobile
LNAPL
Pool
Residual NAPL
Methanogenesis
Aerobic
Respiration
Dentrification
Sulfate
Reduction
Iron (III) Reduction
Plume of Dissolved
Fuel Hydrocarbons
(Source: W,R, N, & W, 1999.)
(Adapted from Lovley et al., 1994b.)
Ground
Water
Flow
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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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Biobed technique
When appyling the biobed technique excavated soil is piled up to beds
(biobeds) where the microbial degradation of contaminants takes place.
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Usually it is aerobic but sometimes we use
an anaerobic bed.
Anaerobic bed:
Structural substances allowing oxygen are
not added to an anaerobic bed.
Instead of it, strongly oxygen-consuming
substances such as e.g. molasses or fresh
compost are added.
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Bioslurping
Removes free contaminant phase (LNAPL) floating on groundwater and also
supports microbial degradation processes. The phase is removed by vacuum.
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Bioventing
The only microbial in-situ technique available for
treating unsaturated soil.
Based on a suction of soil air.
Air enters subsoil, supplies oxygen for aerobic
degradation of contaminants.
Or air may be injected.
Maybe add nutrient salts through salt solutions or
infiltration through horizontal drains. (eg nitrogen
salts)
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Biosparging (Airsparging)
Oil-free atmospheric air is injected into the
aquifer. Air flows into the unsaturated soil
area through an area of fine, small branched
channels.
Biosparging supports:
•in-situ stripping of volatile contaminants,
•desorption of contaminants
•microbial degradation by enriching
groundwater with oxygen.
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Bioscreen (passive microbial in-situ techniques)
Includes
1. in-situ reactive zone , and
2. permeable reactive wall.
In-situ reactive zones (IRZ)
a series of closely arranged groundwater wells
aligned vertically to the groundwater flow direction in the plume
or also to the contamination source.
Electron acceptors (e. g. H2O2/NO3- to degrade non-chlorinated contaminants)
or
Electron donors (e.g. molasses of lactate to force the degradation of chlorinated
contaminants)
Injected into these wells (pulse injections).
Stimulates the microbial population to adapt to a new redox situation and to
degrade contaminant .
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It is also possible to induce various redox zones one behind the other along the
groundwater flow direction where e.g. volatile chlorinated organic compounds
can be completely mineralized.
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Monitoring and efficiency review of
remediation
To be successful need to control the
biogeochemical, hydrogeological and
technological processes.
Monitoring will supervise, and,
Checked if the target of remediation has
been reached.
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A specific monitoring program for each
remediation where the sampling spots,
the frequency of sampling and the
parameters to be analyzed are fixed.
A balance of analyzing (as much as
necessary) and
costs resulting from it (as low as
possible).
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Monitoring of in-situ techniques
Processes in an aquifer have to be
monitored well. Remediation will be only
successful if there is good transport of the
nutrient salts and electron
acceptors/donators to the location of
contamination and the removal of the final
metabolic products (e.g. CO2, N2).
Gas bubbles may be formed in subsoil
affecting the transport processes.
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Parameters to be measured during monitoring:
• contaminants
• metabolites (determined as dissolved organic
carbon; DOC)
• final degradation products (CO2, CH4)
• nutrient salts (z. B. NH4+, PO43-)
• redox indicators (O2, NO3-, NO2-, Fedissolv, Mndissolv
SO42-, S2-),
• electron donators (as a rule, also analyzed as DOC )
• field parameters (pH, redox potential, electric
conductivity, temperature)
• optional: bacterial counts (total count, contaminant
degraders, D. ethenogenes etc.)
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With these data information about the
following processes are obtained:
• biogeochemical state of the aquifer,
• success of addition of electron
acceptors/donators and nutrient salts,
• functionality of remediation measures,
• reaching of the remediation targets.
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