D...

Dechlorination : Removal of chlorine and chemical replacement with hydrogen or hydroxide ions to detoxify a substance.
Declining Growth : A growth phase in which the availability of food begins to limit cell growth.
Decomposers : Organisms which utilize energy from wastes or dead organisms. Decomposers complete the cycle by returning nutrients to the soil or water and carbon dioxide to the air or water.
Deep Well Injection : A process by which waste fluids are injected deep below the surface of the earth.
Degradation : A growth phase in which the availability of food begins to limit cell growth.
Delist : Use of the petition process (1) to have a chemical's toxic designation rescinded; (2) to remove a site from the National Priority List; or (3) to exclude a particular waste from regulation even though it is a listed hazardous waste.
Denitrification : The anoxic biological conversion of nitrate to nitrogen gas. It occurs naturally in surface waters low in oxygen, and it can be engineered in wastewater treatment systems. An anaerobic biological reduction of nitrate nitrogen to nitrogen gas, the removal of total nitrogen from a system, and/or an anaerobic process that occurs when nitrite ions are reduced to nitrogen gas and bubbles are formed as a result of this process. The bubbles attach to the biological floc in the activated sludge process and float the floc to the surface of the secondary clarifiers. This condition is often the cause of rising sludge observed in secondary clarifiers or gravity thickeners. (See Nitrification)
Deoxygenation : The consumption of oxygen by the different aquatic organisms as they oxidized materials in the aquatic environment.
Destruction and Removal Efficiency (DRE) : A percentage that represents the number of molecules of a compound removed or destroyed in an incinerator. A DRE of 99.99% means that 9,999 molecules are destroyed for every 10,000 that enter.
Detritus : Dead plant and animal matter, usually consumed by bacteria, but some remains.
Dew Point : The temperature to which air with a given quantity of water vapor must be cooled to cause condensation of the vapor in the air.
Diatomaceous Earth : A fine, siliceous (made of silica) "earth" composed mainly of the skeletal remains of diatoms (single cell microscopic algae with rigid internal structure consisting mainly of silica). Tests prove that DE leaches unacceptable amounts of silicate into the water for fish health. If used as a filter substance, a silicone removing resin should be employed afterwards.
Diffused Air Aeration : A diffused air activated sludge plant takes air, compresses it, and then discharges the air below the water surface of the aerator through some type of air diffusion device.
Digester : A tank in which sludge is placed to allow decomposition by microorganisms. Digestion may occur under anaerobic (most common) or aerobic conditions.
Discharge : The release of any waste into the environment from a point source. Usually refers to the release of a liquid waste into a body of water through an outlet such as a pipe, but also refers to air emissions.
Discharge Area : An area of land where there is a net annual transfer of water from the ground water to surface water, such as to streams, springs, lakes, and wetlands.
Discrete Settling : Settling in which individual particles settle independently, neither agglomerating or interfering with the settling of the other particles present. This occurs in waters with a low concentration of particles.
Disease : Any impairment of the normal function of an organism.
Disinfection : The destruction or inactivation of pathogenic microorganisms. The process designed to kill most microorganisms in wastewater, including essentially all pathogenic (disease-causing) bacteria. There are several ways to disinfect, with chlorine being the most frequently used in water and wastewater treatment plants.
Dispersion : A stable mixture of particles suspended in a fluid medium.
Dispersion Model : A mathematical prediction of how pollutants from a discharge or emission source will be distributed in the surrounding environment under given conditions of wind, temperature, humidity, and other environmental factors.
Disposal : The discharge, deposit, injection, dumping, spilling, leaking, or placing of any solid waste or hazardous waste into the environment (land, surface water, ground water, and air).
Disposal Facility : A landfill, incinerator, or other facility which receives waste for disposal. The facility may have one or many disposal methods available for use. Does not include wastewater treatment.
Dissolved Oxygen (DO) : Oxygen that is freely available in water to sustain the lives of fish and other aquatic organisms.
Dissolved Solids : Chemical substances either organic or inorganic that are dissolved in a waste stream and constitute the residue when a sample is evaporated to dryness.
Distribution Box : Serves to distribute the flow from the septic tank evenly to the absorption field or seepage pits. It is important that each trench or pit receive an equal amount of flow. This prevents overloading of one part of the system.
Distributor : The rotating mechanism that distributes the wastewater evenly over the surface of a trickling filter or other process unit.
D / I Unit : Deionizing unit, frequntly used to maintain water quality in aquariums. Advantages: does not waste water like the R/O unit, is designed to be hooked up to either a faucet or household piping system, the anion & cation resins can be regenerated (with another expensive unit) indefinitely, and these systems allow a larger water flow (up to 2,000 gallons a day), than an R/O system, but cost dramatically more too.
Domestic Sewage : Water borne wastes normally discharging from the sanitary conveniences of dwellings (including apartment houses and hotels), office buildings, factories, and institutions, free from storm surface water and industrial wastes.
Dose : In terms of monitoring exposure levels, the amount of a toxic substance taken into the body over a given period of time.
Dose Response : How an organism's response to a toxic substance changes as its overall exposure to the substance changes. For example, a small dose of carbon monoxide may cause drowsiness; a large dose can be fatal.
Dump : A land site where wastes are discarded in a disorderly or haphazard fashion without regard to protecting the environment. Uncontrolled dumping is an indiscriminate and illegal form of waste disposal. Problems associated with dumps include multiplication of disease-carrying organisms and pests, fires, air and water pollution, unsightliness, loss of habitat, and personal injury.

E...

Ecology : The study of the relationships between all living organisms and the environment, especially the totality or pattern of interactions; a view that includes all plant and animal species and their unique contributions to a particular habitat.
Ecosystem : The interacting synergism of all living organisms in a particular environment; every plant, insect, aquatic animal, bird, or land species that forms a complex web of interdependency. An action taken at any level in the food chain, use of a pesticide for example, has a potential domino effect on every other occupant of that system.
Effluent : Wastewater discharged from a point source, such as a pipe.
Effluent Based Standards : Standards which set concentration or mass per time limits on the effluent being discharged to a receiving water.
Effluent Guidelines : Technical documents developed by EPA which set discharge limits for particular types of industries and specific pollutants.
Effluent Limitations : Limits on the amounts of pollutants which may be discharged by a facility; these limits are calculated so that water quality standards will not be violated even at low stream flows.
Electronegativity : The potential of an atom to attract electrons when the atom is bonded in a compound. The scale is 0 to 4 with 0 being the most electropositive (low attraction) and 4 being the most electronegative (high attraction).
Electrolytic Process : A process that causes the decomposition of a chemical compound by the use of electricity.
Electrostatic Precipitator : A device which uses an electric field to trap particulate pollutants.
Elementary Reaction : A reaction in which the rate expression corresponds to the stoichiometric equation.
Emergency Broadcasting System (EBS) : Used to inform the public about an emergency and the protective actions to take. The EBS is a service of local radio and television stations, activated as needed and approved by a local emergency management agency.
Emergency and Hazardous Chemical Inventory : An annual report by facilities having one or more extremely hazardous substances or hazardous chemicals above certain weight limits, as specified in Section 311 and 312 of EPCRA.
Emergency Preparedness Coordinator : The local government official designated to be notified immediately of chemical emergencies (e.g., spills, chemical releases, explosions, or fires) under EPCRA.
Emission : The release or discharge of a substance into the environment. Generally refers to the release of gases or particulates into the air.
Emission Standards : Government standards that establish limits on discharges of pollutants into the environment (usually in reference to air).
Emulsion : A liquid mixture of two or more liquid substances not normally dissolved in one another, one liquid held in suspension in the other.
Endangered Species : Animals, plants, birds, fish, or other living organisms threatened with extinction by man-made or natural changes in the environment.
Energy Grade Line : A line that represents the elevation of energy head in feet of water flowing in a pipe, conduit, or channel.
Energy Recovery : To capture energy from waste through any of a variety of processes (e.g., burning). Many new technology incinerators are waste-to-energy recovery units.
Endogenous Respiration : A reduced level of respiration (breathing) in which organisms break down compounds within their own cells to produce the oxygen they need.
Enteric : Of intestinal origin, especially applied to wastes or bacteria.
Environmental Assessment (EA) : A preliminary, written, environmental analysis required by NEPA (see the Federal Law section) to determine whether a federal activity such as building airports or highways would significantly affect the environment; may require preparation of more detailed Environmental Impact Statement.
Environmental Audit : An independent assessment (not conducted by EPA) of a facility's compliance policies, practices, and controls. Many pollution prevention initiatives require an audit to determine where wastes may be reduced or eliminated or energy conserved. Many supplemental environmental projects that offset a penalty use audits to identify ways to reduce the harmful effects of a violation.
Environmental Equity : Equal protection from environmental hazards for individuals, groups, or communities regardless of race, ethnicity, or economic status.
Environmental Impact Statement (EIS) : A document prepared by or for EPA which identifies and analyzes, in detail, environmental impacts of a proposed action. As a tool for decision-making, the EIS describes positive and negative effects and lists alternatives for an undertaking, such as development of a wilderness area. (Required by NEPA - see Federal Law Section).
Environmental Justice : The fair treatment of people of all races, cultures, incomes, and educational levels with respect to the development and enforcement of environmental laws, regulations, and policies. Fair treatment implies that no population should be forced to shoulder a disproportionate share of exposure to the negative effects of pollution due to lack of political or economic strength.
Environmental Resistance : All biotic and abiotic factors combining to limit explosion.
Environmental Response Team (ERT) : EPA s group of highly trained scientists and engineers based in Edison, NJ and Cincinnati, OH who back up the federal On-Scene Coordinator. The ERT's capabilities include multimedia sampling and analysis, hazard assessment, hazardous substance and oil spill cleanup techniques, and technical support.
Enzyme : Organic substances (proteins) produced by living organisms and act as catalysts to speed up chemical changes.
Epidemiologist : A medical scientist who studies the various factors involved in the incidence, distribution, and control of disease in a population.
Epilimnion : The top layer of a lake.
Equalizing basin : A holding basin in which variations in flow and composition of liquid are averaged. Such basins are used to provide a flow of reasonably uniform volume and composition to a treatment unit. Also called a balancing reservoir.
Equivalent : The mass of the compound which will produce one mole of available reacting substance. Thus, for an acid, this would be the mass of acid which will produce one mole of H⁺, for a base, one mole of OH^-.
Erosion : The wearing away of soil by wind or water, intensified by land-clearing practices related to farming, residential or industrial development, road building, or logging.
Escherichia Coli : One of the non-pathogenic coliform organisms used to indicate the presence of pathogenic bacteria in water.
Estuary : A complex ecosystem between a river and near-shore ocean waters where fresh and salt water mix. These brackish areas include bays, mouths of rivers, salt marshes, wetlands, and lagoons and are influenced by tides and currents. Estuaries provide valuable habitat for marine animals, birds, and other wildlife.
Ethers : An organic compound which has two hydrocarbon groups bound by an interior oxygen atom. The general formula is R'-O-R".
Eucaryotic Organisms : Organisms which possess a nuclear membrane. This includes all known organisms except viruses and bacteria.
Eurythermal : Bodies of water which are located at the lower end of a river and are subject to tidal fluctuations.
Evaporation : The conversion of liquid water to water vapor. It occurs on the surface of water bodies such as lakes and rivers and immediately after precipitation events in small depressions and other storage areas.
Evapotranspiration : The sum of evaporation and transpiration. Since it is difficult to measure the two terms independently, they are often grouped as one value.
Explosive Limits (chemical) : The amounts of vapor in air that form explosive mixtures. These limits are expressed as lower and upper values and give the range of vapor concentrations in air that will explode if an ignition source is present.
Exposure : Radiation or pollutants that come into contact with the body and present a potential health threat. The most common routes of exposure are through the skin, mouth, or by inhalation.
Extremely Hazardous Substances (EHS) : Any of 366 (+ or -) chemicals or hazardous substances identified by EPA on the basis of hazard or toxicity and listed under EPCRA. The list is periodically revised.

F...

Facultative : A group of microorganisms which prefer or preferentially use molecular oxygen when available, but are capable of suing other pathways for energy and synthesis if molecular oxygen is not available.
Facultative Anaerobe : A bacterium capable of growing under aerobic conditions or anaerobic conditions in the presence of an inorganic ion ie. SO₄^-2, NO₃^-.
Facultative Pond : The most common type of pond in current use. The upper portion (supernatant) is aerobic, while the bottom layer is anaerobic. Algae supply most of the oxygen to the supernatant.
Fecal Coliform Bacteria : Found in the intestinal tracts of mammals, this bacteria in water or sludge is an indicator of pollution and possible contamination by pathogens.
Feedstock : Raw material supplied to a machine or processing plant from which other products can be made. For example, polyvinyl chloride and polyethylene are raw chemicals used to produce plastic tiles, mats, fenders, cushions, and traffic cones.
Fermentation : Energy production without the benefit of oxygen as a terminal electron acceptor, i.e. oxidation in which the net effect is one organic compound oxidizing another. A type of heterotrophic metabolism in which an organic compound rather than oxygen is the terminal electron (or hydrogen) acceptor. Less energy is generated from this incomplete form of glucose oxidation than is generated by respiration, but the process supports anaerobic growth.
Filamentous Organisms : Organisms that grow in a thread or filamentous form. Common types are Thiothrix, Actinomycetes, and Cyanobacteria (blue-green algae). This is a common cause of sludge bulking in the activated sludge process. Variously known as "pond scum", "blue-green algae", or "moss", when it appears in a pond/lake, and confused with algae because it looks a lot like algae. Cyanobacteria forms a symbiotic relationship with some varieties of algae, making the combination very difficult to combat in lakes and ponds. Filamentous organisms and Actinomycetes will naturally stick to solid surfaces. Common types of Cyanobacteria are: Oscillatoria, Anabaena, and Synechococcus. Other filament formers include: Spirogyra, Cladophora, Rhizoclonium, Mougeotia, Zygnema and Hydrodictyon. Nocardia is another filament former, which causes foaming and interferes with flocculation in a waste treatment plant.
Filter Aid : A chemical (usually a polymer) added to water to help remove fine colloidal suspended solids.
Financial Assurance : A means (such as insurance, guarantee, surety bond, letter of credit, or qualification as a self-insurer) by the operator of a facility such as a landfill to assure financial capability for cleaning up possible environmental releases and closure of that facility.
First Draw : The water that comes out when a faucet in the kitchen or bathroom is first opened, which is likely to have the highest level of lead contamination from old plumbing solder and pipes.
Fixed Solids (FS) : Are the solids that do not volatilize at 550°C.
Fixed Suspended Solids (FSS) : Is the matter remaining from the suspended solids analysis which will not burn at 550°C. It represents the non-filterable inorganic residue in a sample.
Flammable : Describes any material that can be ignited easily and that will burn rapidly.
Flare : A device that burns gaseous materials to prevent them from being released into the environment. Flares may operate continuously or intermittently and are usually found on top of a stack. Flares also burn off methane gas in a landfill.
Flash Point : The lowest temperature at which evaporation of a substance produces enough vapor to form an ignitable mixture with air.
Floating Matter : Matter which passes through a 2000 micron sieve and separates by flotation for an hour.
Floc : Clumps of bacteria and particulate impurities or coagulants that have come together and formed a cluster. Found in aeration tanks and secondary clarifiers.
Flocculant Settling : Settling in which particle concentrations are sufficiently high that particle agglomeration occurs. This results in a reduction in the number of particles and an increase in average particle mass. As agglomeration occurs higher settling velocities result.
Flocculation : The process of forming floc particles when a chemical coagulant or flocculent such as alum or ferric chloride is added to the wastewater.
Floodplain : Mostly level land along rivers and streams that may be submerged by floodwater. A 100-year floodplain is an area which can be expected to flood once in every 100 years.
Flow Equalization System : A device or tank designed to hold back or store a portion of peak flows for release during low-flow periods.
Flue Gas Desulfurization : The removal of sulfur oxides from exhaust gases of a boiler or industrial process; usually a wet scrubbing operation which concentrates hazardous materials in a slurry, requiring proper disposal.
Fluidization : The suspension of particles by sufficient upward velocity of the fluid. During fluidization the gravity force is overcome by a combination of buoyancy and fluid friction.
Flux : The movement of a mass past a surface, plane, or boundary. The units are mass per unit area per unit time or [Kg/m²-hour].
F / M : A ratio of the amount of food to the amount of organisms. Used to control an activated sludge process.
Food Chain : Very simple pathway of nutrient flow. Ex. Carnivore > herbivore > plant.
Fugitive Emissions : Air pollutants released to the air other than those from stacks or vents; typically small releases from leaks in plant equipment such as valves, pump seals, flanges, sampling connections, etc.
Fungicide : A pesticide used to control or destroy fungi on food or grain crops.