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A Glossary Abiotic— Occurring without the involvement of microorganisms. Aerobic respiration— Process whereby microorganisms use oxygen as an electron acceptor to generate energy. Air sparging— Injection of air into ground water to remove volatile chemicals and deliver oxygen, which promotes microbial growth. Air stripping— Above-ground process used to remove volatile contaminants from water. It involves exposing the water surface to a large volume of air, usually by flowing water through a tower in one direction and air through the tower in the opposite direction. Aliphatic hydrocarbon— A compound built from carbon and hydrogen joined in a linear chain. Petroleum products are composed primarily of aliphatic hydrocarbons. Anaerobic respiration— Process whereby microorganisms use a chemical other than oxygen as an electron acceptor. Common ''substitutes" for oxygen are nitrate, sulfate, and iron. Aquifer— An underground geological formation that stores ground water. Aromatic hydrocarbon— A chemical formed from benzene rings, originally called "aromatic" because of benzene's distinctive aroma. Solvents, many types of pesticides, and polychlorinated biphenyls are composed of aromatic hydrocarbons. Bacterium— A single-celled organism of microscopic size. Bacteria
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are ubiquitous in the environment, inhabiting water, soil, organic matter, and the bodies of plants and animals. Benzene— A chemical composed of six carbon atoms arranged in a hexagonal ring, with one hydrogen atom attached to each carbon. Bioaugmentation— The addition of nonnative microorganisms to a site. Biocurtain— A large quantity of organisms grown underground specifically to stop contaminant migration by creating localized clogging. Biodegradation— Biologically mediated conversion of one compound to another. Biomass— Total mass of microorganisms present in a given amount of water or soil. Bioremediation— Use of microorganisms to control and destroy contaminants. Biotransformation— Microbially catalyzed transformation of a chemical to some other product. Bioventing— Circulation of air through the subsurface to remove volatile contaminants and provide oxygen, which stimulates microorganisms to degrade remaining contaminants. BTEX— Acronym for benzene, toluene, ethylbenzene, and xylenes, which are compounds present in gasoline and other petroleum products, coal tar, and various organic chemical product formulations. Carbon treatment— Above-ground process for removing contaminants from water or air. It involves contact between the water or air and activated carbon, which adsorbs the contaminants, usually by flowing the water or air through columns packed with carbon. Carbonate— Any chemical containing the CO32- group; limestone and dolomite are examples of rocks formed primarily from carbonate minerals. Chlorinated solvent— A hydrocarbon in which chlorine atoms substitute for one or more hydrogen atoms in the compound's structure. Chlorinated solvents commonly are used for grease removal in manufacturing, dry cleaning, and other operations. Examples include trichloroethylene, tetrachloroethylene, and trichloroethane. Cometabolism— A reaction in which microbes transform a contaminant even though the contaminant cannot serve as an energy source for the organisms. To degrade the contaminant, the microbes require the presence of other compounds (primary substrates) that can support their growth. Complexing agent— A chemical agent that chemically bonds with a
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positively charged molecule, such as a metal. Complexing agents can be used to dissolve precipitated metals. Conservative tracer— A chemical that does not undergo microbiological reactions but has transport properties similar to those of microbiologically reactive chemicals (such as the contaminant and oxygen). Dechlorinate— The removal of chlorine atoms from a compound. Desorption— Opposite of sorption; the dissolution of chemicals from solid surfaces. Deuterium— Hydrogen isotope with twice the mass of ordinary hydrogen; it contains one proton and one neutron in its nucleus. Diauxy— Selective biodegradation of some organic compounds over others, which sometimes occurs when the compounds are present in mixtures. DNA (deoxyribonucleic acid)— Substance within a cell that passes hereditary information from one generation to the next. Electron— A negatively charged subatomic particle that may be transferred between chemical species in chemical reactions. Every chemical molecule contains electrons and protons (positively charged particles). Electron acceptor— Compound that receives electrons (and therefore is reduced) in the energy-producing oxidation-reduction reactions that are essential for the growth of microorganisms and bioremediation. Common electron acceptors in bioremediation are oxygen, nitrate, sulfate, and iron. Electron donor— Compound that donates electrons (and therefore is oxidized) in the energy-producing oxidation-reduction reactions that are essential for the growth of microorganisms and bioremediation. In bioremediation the organic contaminant often serves as an electron donor. Engineered bioremediation— Type of bioremediation that stimulates the growth and biodegradative activity of microorganisms by adding nutrients, electron acceptors, or other stimulants to the site using an engineered system. Enzyme— A protein created by living organisms to use in transforming a specific compound. The protein serves as a catalyst in the compound's biochemical transformation. Enzyme induction— Process whereby an organism synthesizes an enzyme in response to exposure to a specific chemical, the inducer. Equilibrium—Condition in which a reaction has occurred to its maximum extent.
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Ex situ— Latin term referring to the removal of a substance from its natural or original position. Fermentation— Process whereby microorganisms use an organic compound as both electron donor and electron acceptor, converting the compound to fermentation products such as organic acids, alcohols, hydrogen, and carbon dioxide. Fixation— Process whereby microorganisms obtain carbon for building new cells from inorganic carbon, usually carbon dioxide. Free product recovery— Removal of residual pools of contaminants, such as gasoline floating on the water table, from the subsurface. Gas chromatograph— Instrument used to identify and quantify volatile chemicals in a sample. Gene probe— One class of oligonucleotide probes. Gene probes are used to identify the presence of a particular gene (such as the gene responsible for a particular biodegradative reaction) on the cell's DNA. Genetically engineered organism— An organism whose genes have been altered by humans. For example, researchers have used genetic engineering to give bacteria the capability to degrade hazardous chemicals that normally resist biodegradation. Glacial outwash— Materials (typically sand and gravel) deposited during the melting of glaciers. Halogenate— Replacement of one or more hydrogen atoms on a chemical compound with atoms of a halogen, such as chlorine, fluorine, or bromine. High-performance liquid chromatograph— Instrument used to identify and quantify contaminants in a sample. Hydraulic conductivity— A measure of the rate at which water moves through a unit area of the subsurface under a unit hydraulic gradient. Hydraulic gradient— Change in head (i.e., water pressure) per unit distance in a given direction, typically in the principal flow direction. Hydrocarbon— A chemical composed of carbon and hydrogen in any of a wide variety of configurations. Petroleum products, as well as many synthetic industrial chemicals, contain many different hydrocarbons. Hydrophobic compound— A "water-fearing" compound, such as oil, that has low solubility in water and tends to form a separate phase.
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In situ— Latin term meaning "in place"—in the natural or original position. Infiltration gallery— Engineered system used to deliver materials that stimulate microorganisms in the subsurface. Infiltration galleries typically consist of buried perforated pipes through which water containing the appropriate stimulating materials is pumped. Inorganic compound— A chemical that is not based on covalent carbon bonds. Important examples are metals, nutrients such as nitrogen and phosphorus, minerals, and carbon dioxide. Intrinsic bioremediation— A type of in situ bioremediation that uses the innate capabilities of naturally occurring microbes to degrade contaminants without taking any engineering steps to enhance the process. Intrinsic permeability— A measure of the relative ease with which a liquid will pass through a porous medium. Intrinsic permeability depends on the shape and size of the openings through which the liquid moves. Isotope— Any of two or more species of an element in the periodic table with the same number of protons. Isotopes have nearly identical chemical properties but different atomic masses and physical properties. For example, the isotope carbon 12 has six protons and six neutrons, while the isotope carbon 13 has six protons and seven neutrons. Both have atomic number 6 (the number of protons), but carbon 13 is more massive than carbon 12 because it carries an extra neutron. Isotope fractionation— Selective degradation by microorganisms of one isotopic form of a carbon compound over another isotopic form. For example, microorganisms degrade the 12C isotopes of petroleum hydrocarbons more rapidly than the 13C isotopes. Kinetics— Refers to the rate at which a reaction occurs. Land farming— Above-ground process used to stimulate microorganisms to degrade contaminants in soil. The process involves spreading out the soil, adding nutrients, and tilling. Ligand— See "complexing agent." Mass spectrometer— Instrument used to identify the chemical structure of a compound. Usually, the chemicals in the compound are separated beforehand by chromatography. Metabolic intermediate— A chemical produced by one step in a multistep biotransformation.
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Metabolism— The chemical reactions in living cells that convert food sources to energy and new cell mass. Methanogen— A microorganism that produces methane. Because they thrive without oxygen, methanogens can be important players in subsurface biotransformations, where oxygen is often absent. Micelle— An aggregate of molecules, such as surfactant molecules, that form a small region of nonaqueous-phase within an otherwise aqueous matrix. Microcosm— A laboratory vessel set up to resemble as closely as possible the conditions of a natural environment. Microorganism— An organism of microscopic or submicroscopic size. Microorganisms can destroy contaminants by using them as "food sources" for their own growth and reproduction. Mineralization— The complete degradation of an organic chemical to carbon dioxide, water, and possibly other inorganic compounds. Most-probable-number (MPN) technique— A statistical technique for estimating the number of organisms present in a sample. Nonaqueous-phase liquid— A liquid solution that does not mix easily with water. Many common ground water contaminants, including chlorinated solvents and many petroleum products, enter the subsurface in nonaqueous-phase solutions. Oligonucleotide probe— A short piece of DNA that can be used to identify the genetic makeup of microorganisms in a sample and the reactions they are capable of carrying out. Organic compound— A compound built from carbon atoms, typically linked in chains or rings. Oxidization— Transfer of electrons away from a compound, such as an organic contaminant. The oxidation can supply energy that microorganisms use for growth and reproduction. Often (but not always), oxidation results in the addition of an oxygen atom and/or the loss of a hydrogen atom. Petroleum hydrocarbon— A chemical derived from petroleum by various refining processes. Examples include gasoline, fuel oil, and a wide range of chemicals used in manufacturing and industry. Plume— A zone of dissolved contaminants. A plume usually originates from the contaminant zone and extends for some distance in the direction of ground water flow. Primary substrates— The electron donor and electron acceptor that are essential to ensure the growth of microorganisms. These com-
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pounds can be viewed as analogous to the food and oxygen that are required for human growth and reproduction. Protozoan— A single-celled organism that is larger than a bacterium and may feed on bacteria. Pump-and-treat system— Most commonly used type of system for cleaning up contaminated ground water. Pump-and-treat systems consist of a series of wells used to pump contaminated water to the surface and a surface treatment facility used to clean the extracted ground water. Rate-limiting material— Material whose concentration limits the rate at which a particular process can occur. Reduction— Transfer of electrons to a compound, such as oxygen. It occurs when another compound is oxidized. Reductive dehalogenation— A variation on biodegradation in which microbially catalyzed reactions cause the replacement of a halogen atom on an organic compound with a hydrogen atom. The reactions result in the net addition of two electrons to the organic compound. Reporter gene— A tool used with genetically engineered microorganisms. When a reporter gene is incorporated into a microorganism's genetic material, it provides a signal when the organism is present and active. An example is a gene that produces a protein that causes the microorganism to emit light. Saturated zone— Part of the subsurface that is beneath the water table and in which the pores are filled with water. Secondary substrate— A chemical that can be transformed by microorganisms through secondary utilization. Secondary utilization— General term for the transformation of contaminants by microorganisms when the transformation yields little or no benefit to the organisms. Slurry wall— A clay barrier constructed in the subsurface to prevent the spread of contaminants by preventing water flow. Soil vapor extraction— See "Vapor recovery." Sorption— Collection of a substance on the surface of a solid by physical or chemical attraction. Substrate— A compound that microorganisms can use in the chemical reactions catalyzed by their enzymes. Sulfate reducer— A bacterium that converts sulfate to hydrogen sulfide. Because they can act without oxygen, sulfate-reducing bacteria can be important players in the oxygen-limited subsurface. Surfactant— Soap or a similar substance that has a hydrophobic and
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a hydrophilic end. Surfactants can bond to oil and other immiscible compounds to aid their transport in water. Unavailability— Situation in which a contaminant is sequestered from the microorganism, inhibiting the organism's ability to degrade the contaminant. Unsaturated zone— Soil above the water table, where pores are partially or largely filled with air. Vadose zone— See "Unsaturated zone." Vapor recovery— A method for removing volatile contaminants from the soil above the water table by circulating air through the soil. Volatilization— Transfer of a chemical from the liquid to the gas phase (as in evaporation).
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B Biographical Sketches of Committee Members and Staff BRUCE E. RITTMANN, committee chair, is the John Evans Professor of Environmental Engineering at Northwestern University and an active researcher and teacher in the field of environmental biotechnology. His special interests include biofilm kinetics, microbial ecology, in situ bioremediation, biological drinking water treatment, and the fate of hazardous organic chemicals. Dr. Rittmann was a member of the National Research Council committee that authored Ground Water Models: Scientific and Regulatory Applications. He recently served as president of the Association of Environmental Engineering Professors. LISA ALVAREZ-COHEN, assistant professor of environmental engineering at the University of California, Berkeley, received a Ph.D. in environmental engineering and science from Stanford University in 1991 and a B.A. in engineering and applied science from Harvard University in 1984. Dr. Alvarez-Cohen's research interests are modeling of microbial processes in porous media, bioremediation of contaminated aquifers, innovative hazardous waste treatment technologies, and application of cometabolic biotransformation reactions. PHILIP B. BEDIENT, Shell Distinguished Professor of Environmental Science at Rice University, received a B.S. in physics in 1969, an M.S. in environmental engineering in 1972, and a Ph.D. in environmental engineering sciences in 1975 from the University of Florida.
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His primary research interests include ground water pollutant transport modeling and hazardous waste site evaluation. RICHARD A. BROWN, vice president of remediation technology for Groundwater Technology, Inc., in Trenton, New Jersey, received a B.A. in chemistry from Harvard University and a Ph.D. in inorganic chemistry from Cornell University. His responsibilities include the development and implementation of remediation technologies such as bioremediation, soil vapor extraction, and air sparging. Before joining Groundwater Technology, Dr. Brown was director of business development for Cambridge Analytical Associates' Bioremediation Systems Division and technology manager for FMC Corporation's Aquifer Remediation Systems. Dr. Brown holds patents on applications of bioreclamation technology, on the use of hydrogen peroxide in bioreclamation, and on an improved nutrient formulation for the biological treatment of hazardous wastes. FRANCIS H. CHAPELLE, a researcher at the U.S. Geological Survey in Columbia, South Carolina, received a Ph.D. in hydrology in 1984 from George Washington University. He also holds a B.A. in music and a B.S. in geology from the University of Maryland. Currently, he studies the impacts of subsurface microbiology on ground water chemistry. PETER K. KITANIDIS, professor of civil engineering at Stanford University, received a B.S. in civil engineering in 1974 from the National Technical University of Athens, Greece, an M.S. in civil engineering in 1976 from the Massachusetts Institute of Technology, and a Ph.D. in water resources in 1978, also from MIT. His current research focuses on the use of geostatistical and predictive ground water hydrology methods for designing water quality monitoring networks. He is also conducting research on the design of nutrient circulation systems for stimulating subsurface microorganisms to degrade ground water contaminants. EUGENE L. MADSEN, assistant professor in the Section of Microbiology, Division of Biological Sciences, at Cornell University, received B.A., B.S., and M.S. degrees from the University of California at Santa Cruz, Oregon State University, and Cornell University, respectively. His Ph.D. from Cornell in 1985 is in soil science, microbiology, and ecology. Since 1989, as a researcher at Cornell, he has pursued interests in ground water microbiology, microbial metabolism of environmental pollutants, and developing criteria for proving in situ biodegradation. Prior to returning to Cornell, he held research appointments at Rutgers and Penn State universities and at an environmental restoration company in Bozeman, Montana. WILLIAM R. MAHAFFEY, vice president of the technology de-
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partment for ECOVA Corporation in Redmond, Washington, earned a B.S. in microbiology in 1976 and an M.S. in microbial ecology in 1978 from the State University of New York. He holds a Ph.D. in microbial biochemistry, earned in 1986, from the University of Texas. Dr. Mahaffey serves as technical principal on all of ECOVA's bioremediation projects. He directs the activities of project microbiologists, develops operating parameters for the use of enhanced biodegradation in the field, and reviews all company projects involving bioremediation. ROBERT D. NORRIS, technical director of bioremediation at Eckenfelder, Inc., in Nashville, Tennessee, received a B.S. in chemistry from Beloit College and a Ph.D. in organic chemistry from the University of Notre Dame. He has been involved since 1983 in the development and implementation of a variety of bioremediation processes and holds 13 U.S. patents, including four on various aspects of bioremediation. He has developed and conducted laboratory and pilot tests as well as successful in situ and ex situ bioremediation under a range of conditions. JOSEPH P. SALANITRO, senior staff research microbiologist at Shell Development Company in Houston, Texas, holds a Ph.D. in microbiology from Indiana University. During his 21-year career with Shell, he has been involved in both the chemical and oil sectors of environmental research, studying the aerobic and anaerobic biodegradability of detergents, chemicals, pesticides and petrochemical waste effluents, and the role of microbes and sour gas formation in oil field waterfloods. His current research interests are in defining the potential and limits of biodegradation of gasoline components in subsurface remediation. JOHN M. SHAUVER, environmental enforcement manager for the Michigan Department of Natural Resources, earned a B.S. in fisheries biology from Michigan State University and did two years of postgraduate work in geology. A 24-year veteran of the Department of Natural Resources (minus a two-year absence for military duty from 1968 until 1970), he has worked as a water quality investigator, hazardous waste cleanup specialist, aquatic biologist, environmental law enforcement specialist, and environmental enforcement manager. JAMES M. TIEDJE, director of the Center for Microbial Ecology at Michigan State University, received a B.S. in agronomy in 1964 from Iowa State University. He received an M.S. in 1966 and a Ph.D. in 1968 in soil microbiology from Cornell University. He is currently a professor in the Departments of Crop and Soil Sciences and Microbiology and Public Health at Michigan State University. His expertise is in microbial ecology, and he conducts research in three focal
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areas: denitrification, reductive dehalogenation, and the use of gene probes to study community selection in nature. JOHN T. WILSON, research microbiologist at the U.S. Environmental Protection Agency's R. S. Kerr Laboratory in Ada, Oklahoma, earned a B.S. in biology in 1969 from Baylor University, an M.A. in microbiology in 1971 from the University of California at Berkeley, and a Ph.D. in microbiology in 1978 from Cornell University. His areas of expertise are bioremediation and subsurface microbiology, with emphasis on quantitative description of the biological and physical processes that control the behavior of hazardous materials in soils and the subsurface. RALPH S. WOLFE, a professor of microbiology at the University of Illinois since 1955, received a Ph.D. at the University of Pennsylvania in 1953. A member of the National Academy of Sciences, his major research interest has been anaerobic microbial metabolism. He was attracted to the study of methanogenic bacteria in 1961 because their biochemistry was unknown, and the difficulty of isolating and cultivating these extremely oxygen-sensitive anaerobes was legendary. Dr. Wolfe developed a system for mass culture of methanogens in kilogram quantities, obtained the first formation of methane by a cell-free extract, and evolved a simplified procedure for the routine culture of methanogens in a pressurized atmosphere of hydrogen and carbon dioxide—a technique that has played a pivotal international role in development of the field. JACQUELINE A. MACDONALD, program officer at the National Research Council's Water Science and Technology Board, served as study director and managing editor for the Committee on In Situ Bioremediation. She holds an M.S. in environmental science in civil engineering from the University of Illinois and a B.A., magna cum laude, in mathematics from Bryn Mawr College. GREGORY K. NYCE, senior project assistant at the National Research Council's Water Science and Technology Board, served as project assistant for the Committee on In Situ Bioremediation. He received his B.S. in psychology from Eastern Mennonite College.
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