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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

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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Microorganism

InputsOutputs

Boundary

Organic pollutant &Oxidized electron

Acceptor (O2)

Energy

Environment

CO2 + H2O + other waste Products +

Reduced electron Acceptor (H2O)

Energy

Feedback

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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 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 neededBioremediation 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 e-

H2 is the electron donor

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Microorganism

InputsOutputs

Boundary

Electron donor (sugar, fatty acid, H2) &

Electron acceptor (electrophilic pollutant)

Energy

Environment

Oxidized electron donorCO2 + H2O and

other fermentation products +

Less halogenated pollutant and Cl-

Energy

Feedback

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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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GroundWaterFlow

Plume 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.)

2. Some oil is spilt on the ground

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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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From: Atlas and Bartha, 1998From: Atlas and Bartha, 1998

4. Breaking aromatic rings

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Organic Carbon

Oxidized Product

Oxidation to yieldenergy; can be multiple

steps

e-

Terminal e- Acceptor

Reduced Product

Reduction toprovide e- “sink”(costs energy)

General Metabolic Redox Model in Microorganisms

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Organic Carbon

CO2

e-

O2

H2O

Energyproduction; multiple steps

Aerobic respiration

General Model for Aerobic Respiration

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CH4

CH3OH

e-

O2

H2O

Energyproduction

Coupledreduction

Aerobic Respiration: Examples and Cometabolism

Benzene

CO2

Energyproduction

TCE

CO2

No energyproduction; cometabolism