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Вы можете ознакомиться и скачать презентацию на тему Bioremediation. Доклад-сообщение содержит 38 слайдов. Презентации для любого класса можно скачать бесплатно. Если материал и наш сайт презентаций Mypresentation Вам понравились – поделитесь им с друзьями с помощью социальных кнопок и добавьте в закладки в своем браузере.

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Bioremediation Natalie L. Capiro October 21, 2003

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What is Bioremediation?? Using subsurface microorganisms to transform hazardous contaminants into relatively harmless byproducts, such as ethene and water Biodegrade Mineralize Biotransform Techniques or types of bioremediation: A component of Natural Attenuation Enhanced Bioremediation Bioaugmentation

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Bioremediation Background Natural Attenuation is Not fast enough, Not complete enough, Not frequently occurring enough to be broadly used for some compounds, especially chlorinated solvents The current trend is to stimulate/enhance a site’s indigenous subsurface microorganisms by the addition of nutrients and electron donor In some cases, bioaugmentation is necessary when metabolic capabilities are not naturally present.

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Historical Perspective ~1900 Advent of biological processes to treat organics derived from human or animal wastes (and the sludges produced) ~1950 Approaches to extend wastewater treatment to industrial wastes ~1960 Investigations into the bioremediation of synthetic chemicals in wastewaters ~1970 Application in hydrocarbon contamination such as oil spills and petroleum in groundwater ~1980 Investigations of bioremediation applications for substituted organics ~1990 Natural Attenuation of ’70 and ’90, and the development of barrier approaches ~2000 High-rate in situ bioremediation; source zone reduction; bioaugmentation

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Soil and Subsurface Contaminants Benzene and related fuel components (BTEX) Pyrene and other polynuclear aromatics Chlorinated aromatics and solvents Herbicides and pesticides Nitroaromatic explosives and plasticizers

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Sources of Contamination Industrial spills and leaks Surface impoundments Storage tanks and pipes Landfills Burial areas and dumps Injection wells

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Current Water Issues Associated with Gasoline Use Widespread contamination Major treat to drinking water resources Components of fuels are known carcinogens Current fuel oxygenate, MTBE, very mobile and not very degradable Ethanol is due to replace MTBE, but its behavior in the subsurface is not yet understood

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Typical Fuel (BTEX) Spill

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Chlorinated Background Groundwater plumes of chlorinated solvents are widespread due to their extensive use at industrial, DOD, and dry cleaner sites. Chlorinated compounds commonly exist as dense nonaqueous-phase liquids (DNAPLs) that act as long-term, continuing sources that slowly solubilize into groundwater. Known carcinogenic and toxic effects Not a primary substrate for any known bacteria

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Routes of DNAPL Migration

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DNAPL Our Most Difficult Challenge DNAPL source Residual phase Trapped on lenses Pools in low areas Creates soluble plumes for years Extremely hard to remediate

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Treatment Techniques Soil Extraction Pump and Treat Physical and/or reactive barriers Air and Hydrogen Sparging Biological (microbes) Chemical (surfactants)

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Why use Bioremediation? No additional disposal costs Low maintenance Does not create an eyesore Capable of impacting source zones and thus, decreasing site clean-up time

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Source Zone Treatment vs. Plume Treatment

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Fundamentals of Biodegradation All organics are biodegradable, BUT biodegradation requires specific conditions There is no Superbug Contaminants must be bioavailable Biodegradation rate and extent is controlled by a “limiting factor”

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Biotic Transformations Result of metabolic activity of microbes Aerobic and anaerobic biodegradation Reduces aqueous concentrations of contaminant Reduction of contaminant mass Most significant process resulting in reduction of contaminant mass in a system

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Bioremediation Processes Conversion of contaminants to mineralized (e.g. CO2, H2O, and salts) end-products via biological mechanisms Biotransformation refers to a biological process where the end-products are not minerals (e.g., transforming TCE to DCE) Biodegradation involves the process of extracting energy from organic chemicals via oxidation of the organic chemicals

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How Microbes Use the Contaminant Contaminants may serve as: Primary substrate enough available to be the sole energy source Secondary substrate provides energy, not available in high enough concentration Cometabolic substrate fortuitous transformation of a compound by a microbe relying on some other primary substrate

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Requirements for Microbial Growth

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Electron Exchange

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Aerobic v. Anaerobic If oxygen is the terminal electron acceptor, the process is called aerobic biodegradation All other biological degradation processes are classified as anaerobic biodegradation In most cases, bacteria can only use one terminal electron acceptor Facultative aerobes use oxygen, but can switch to nitrate in the absence of oxygen

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Bacterial Metabolism Aerobic Oxidation Cometabolism

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Electron Acceptor Zones After O2 is depleted, begin using NO3– Continue down the list in this order O2 ––> NO3– ––> Fe3+ ––> SO42– ––> CO2

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Electron Acceptor Condition

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Bioremediation Practice Understand physical and chemical characteristics of the contaminants of interest Understand the possible catabolic pathways of metabolism and the organisms that possess that capability Understand the environmental conditions required to: Promote growth of desirable organisms Provide for the expression of needed organisms Engineer the environmental conditions needed to establish favorable conditions and contact organisms and contaminants

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Oxygen is of Primary Importance Most of the time oxygen is the primary factor limiting in situ biodegradation In most cases if adequate oxygen can be supplied then biodegradation rates are adequate for remediation Other limiting factors exist, but are usually secondary to oxygen

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Two ways to introduce oxygen in situ Dissolved in water : Actively pumped: H2 O2 , aerated water Passively: ORC ® , membrane, aeration In gaseous form, usually air Bioventing above the water table Air sparging below the water table

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Dehalogenation Stripping halogens (generally Chlorine) from an organic molecule Generally an anaerobic process, and is often referred to as reductive dechlorination R–Cl + 2e– + H+ ––> R–H + Cl– Can occur via Dehalorespiration (anaerobic) Cometabolism (aerobic)

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Dehalorespiration Certain chlorinated organics can serve as a terminal electron acceptor, rather than as a donor Confirmed only for chlorinated ethenes Rapid, compared to cometabolism High percentage of electron donor goes toward dechlorination Dehalorespiring bacteria depend on hydrogen-producing bacteria to produce H2, which is the preferred primary substrate

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Reductive Dechlorination

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Added Danger Dechlorination of PCE and TCE should be encouraged, but monitored closely The dechlorination products of PCE are more hazardous than the parent compound DCE is 50 times more hazardous than TCE Vinyl Chloride is a known carcinogen

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Cometabolism Fortuitous transformation of a compound by a microbe relying on some other primary substrate Generally a slow process - Chlorinated solvents don’t provide much energy to the microbe Most oxidation is of primary substrate, with only a few percent of the electron donor consumption going toward dechlorination of the contaminant Not all chlorinated solvents susceptible to cometabolism (e.g., PCE and carbon tetrachloride)