Groundwater Pollution Bioremediation – Cleaning up simple organic chemicals

Pollution of air, water and soil is a worldwide problem Picture: http://upload.wikimedia.org/wikipedia/commons/b/b3/Pollution_over_east_China.jpg

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

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

Bioremediation is when organisms either metabolize or fix contaminants

Less harmful chemicals Contaminant Organisms

Contaminants are fixed Organisms

Bioremediation is any process that uses microorganisms, fungi, green plants or their enzymes to return the contaminated environment to its original condition.

Because there is too much of something we need to either reduce it or immobilize (fix) it

Reducing pollution can mean degrading it or changing its form

Less harmful chemicals Contaminant Organisms

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.

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 + ?

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

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?

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

Bioremediation might be improved We could add more or better organisms to the soil (bioaugmentation)

We could help the organisms grow by changing things in the environment (biostimulation)

How could we stimulate the growth of microorganisms?

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

Other Names Bioremediation is also called enhanced (늘리다) bioremediation or engineered bioremediation.

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

BTEX (Benzene, Toluene, Ethylbenzene, and Xylenes) are monoaromatic hydrocarbons which are in petroleum and petroleum products such as gasoline.

If there is enough oxygen more degradation can happen

… and so on What does each number stand for?

If there is enough oxygen they can degrade to water and carbondioxide 2C6H6 + 15O2 12CO2 + 6H2O

See the redox reaction. This gives the cell energy.

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

Aerobic is often faster than anaerobic degradation However, many compounds can only be metabolized under reductive conditions. Then anaerobic metabolism is needed.

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.

Remember the degrading of tetrachloroethene

Anaerobic = no oxygen Tetrachloroethene is reduced with e- H2 is the electron donor

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.

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.

How can we engineer the conditions to stimulate bioremediation?

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.

How can we follow what is happening?

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).

We can count this, this or this. Less harmful chemicals Contaminant Organisms We can count this, this or this.

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)

Perchlorates are the salts of perchloric acid (HClO4). They are commonly found in rocket fuel and explosives, often those used by the military.

Advantages of Bioremediation It may result in complete degradation of organic compounds to nontoxic byproducts. Not much equipment is needed It 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.

Advantage 우위 Toxic ≠ nontoxic (not toxic) equipment 설비 in-situ 원위치 ≠ ex-situ

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 measuring biodegradation rates. It may be difficult to control volatile organic compounds during ex-situ bioremediation process Generally requires longer treatment time as compared to other remediation technologies.

Partial 불완전한 Mobile 가동성의 Rate 속도, 진도

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.

Order of Acceptors Usually electron acceptors are used by bacteria in order of their thermodynamic energy yield : oxygen, nitrate, iron, sulfate, carbon dioxide.

Order of Acceptors Ground Water Flow Mobile LNAPL Pool Residual NAPL Methanogenesis Aerobic Respiration Sulfate Reduction Dentrification Iron (III) Reduction Ground Water Flow Plume of Dissolved Fuel Hydrocarbons (Source: W,R, N, & W, 1999.) (Adapted from Lovley et al., 1994b.)

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

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.

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.

Not Too Much Toxin Too 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.

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'