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Groundwater Pollution

Bioremediation – Cleaning up simple organic chemicals

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Pollution of air, water and soil is a worldwide problem

Picture: http://upload.wikimedia.org/wikipedia/commons/b/b3/Pollution_over_east_China.jpg

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The pollution of groundwater by organic chemicals affects an estimated 300,000 to 400,000 contaminated sites in the USA alone

Picture: http://commons.wikimedia.org/wiki/Image:Drainage_nitrates_vers_HondeghemFr_2003_04_09.jpg

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Problems occur when there is too much of something in the environment

Carbon dioxide emissions in thousands of metric tons http://commons.wikimedia.org/wiki/Image:Countries_by_carbon_dioxide_emissions_world_map.PNG

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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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Reducing pollution can mean degrading it or changing its form

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Contaminant Organisms Less harmful chemicals

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Bioremediation of chlorinated ethenes uses microorganisms to break down contaminants to less toxic end products

PCE (Tetrachloroethene), which contains four chlorine atoms, is degraded from PCE to TCE to DCE (dichloroethene) to VC (vinyl chloride) to ethene. DCE and VC are toxic but ethene is not toxic.

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The organisms make chemical reactions happen

Balance these reactionsBenzene (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 reactionsBenzene (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 need 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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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 by-products

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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… and so on

What does each number stand for?

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If there is enough oxygen they can degrade to water and carbondioxide

2C6H6 + 15O2 12CO2 + 6H2O

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See the redox reaction. This gives the cell energy.

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Oxidation can occur without O2 oxygen Oxidation is when a chemical accepts an electron of another chemical.

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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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Reductive Dehalogenation

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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Remember 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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Reduction of Halogens

Highly electrophilic compounds such as halogenated aliphatics and explosives often are bioremediated through reductive processes that remove the electrophilic halogen or nitro groups.

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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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How can we engineer the conditions to stimulate bioremediation?

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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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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. ethene from the reductive dechlorination of tetrachloroethene).

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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 neededIt can be in-situ or ex-situ. In-situ bioremediation is safer because contaminated soils don’t have to be moved. In-situ 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 (not toxic)

equipment 설비

in-situ 원위치 ≠ ex-situ

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Disadvantages of BioremediationThere 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 measuring biodegradation rates.It may be difficult to control volatile organic compounds during ex-situ bioremediation processGenerally 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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Processes

Bioremediation processes may be directed towards accomplishing:

–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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Order of Acceptors

Usually electron acceptors are used by bacteria in order of their thermodynamic energy yield :

oxygen,

nitrate,

iron,

sulfate,

carbon dioxide.

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GroundWaterFlowPlume of

Dissolved Fuel Hydrocarbons

Residual NAPLMobile LNAPL Pool

Methanogenesis

SulfateReduction

Iron (III) Reduction

Dentrification

Aerobic Respiration

(Source: W,R, N, & W, 1999.) (Adapted from Lovley et al., 1994b.)

Order of Acceptors

55http://mn.water.usgs.gov/bemidji/results/fact-sheet.pdf

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Reduction Zones

Oxygen and nitrate are highly energetic but they are used rapidly.

Their reduction zones frequently do not go deeply into contaminated zones particularly in heavily polluted areas.

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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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Not Too Much ToxinToo much contaminant can be toxic to microbes.

Some may be toxic even at low concentrations.

We can try to dilute contaminants.

We can try to find acclimated microbes.

We can try to change the bioavailability of the toxin.

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BIOREMEDIATION OF CONTAMINATED SITES

Karl J. Rockne and Krishna R. Reddy

University of Illinois at Chicago

Department of Civil and Materials Engineering

842 West Taylor Street

Chicago, Illinois 60607, USA

http://www.uic.edu/classes/cemm/cemmlab/bioremed-india-2003.pdf#search='BIOREMEDIATION%20OF%20CONTAMINATED%20SITES'