Technical Resources

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Symbols and Acronyms

E. coli   See Escherichia coli.

eductor  A device for mixing air with water; a liquid pump operating under a jet principle, using liquid under pressure as the operating medium to entrain air in the liquid. See also ejector.

effective size  The diameter of the particles, spherical in shape, equal in size, and arranged in a given manner, of a hypothetical sample of granular material that would have the same transmission constant as the actual material under consideration. There are a number of methods for determining effective size, the most common being that developed by Allen Hazen, which consists of passing the granular material through sieves with varying dimensions of mesh. In this method, the effective size is determined from the dimensions of that mesh, which permits 10% of the sample to pass and will retain the remaining 90%; in other words, the effective size is that for which 10% of the grains are smaller and 90% larger.

effervescence  The vigorous escape of small gas bubbles from a liquid, especially as a result of chemical action.

efficiency  The relative results obtained in any operation in relation to the energy or effort required to achieve such results. It is the ratio of the total output to the total input, expressed as a percentage.

effluent  Wastewater or other liquid, partially or completely treated or in its natural state, flowing out of a reservoir, basin, treatment plant, or industrial treatment plant, or part thereof.

effluent quality  The physical, biological, and chemical characteristics of a wastewater or other liquid flowing out of a basin, reservoir, pipe, or treatment plant.

ejector  A device for moving a fluid or solid by entraining it in a high-velocity stream or air or water jet.

elbow  A pipe fitting that connects two pipes at an angle. The angle is always 90 deg unless another angle is stated. Also called an ell.

electromotive force  The property of a physical device that tends to produce an electrical current in a circuit. It is the moving force that causes current to flow (see volt).

elevation head  The energy possessed per unit weight of a fluid because of its elevation above some point. Also called position head or potential head.

elutriation  A process of sludge conditioning whereby the sludge is washed with either fresh water or plant effluent to reduce the demand for conditioning chemicals and to improve the settling or filtering characteristics of the solids. Excessive alkalinity is removed in this process.

emission  Discharge of a liquid, solid, or gaseous material.

emulsifying agent  An agent capable of modifying the surface tension of emulsion droplets to prevent coalescence. Examples are soap and other surface-active agents, certain proteins and gums, water-soluble cellulose derivatives, and polyhydric alcohol esters and ethers.

emulsion  A heterogeneous liquid mixture of two or more liquids not normally dissolved in one another, but held in suspension one in the other by forceful agitation or by emulsifiers that modify the surface tension of the droplets to prevent coalescence.

endogenous respiration  Autooxidation by organisms in biological processes.

energy (electrical)  As commonly used in the utility industry, electrical energy means kilowatt-hours.

Enterococci  A group of Cocci that normally inhabit the intestines of man and animals. Incorrectly used interchangeably with fecal Streptococci.

entrainment  The carryover of drops of liquid during processes such as distillation. The trapping of bubbles in a liquid produced either mechanically through turbulence or chemically through a reaction.

enzyme  A catalyst produced by living cells. All enzymes are proteins, but not all proteins are enzymes.

epidemic  A disease that occurs simultaneously in a large fraction of the community.

equalization  In wastewater systems, the storage and controlled release of wastewaters to treatment processes at a controlled rate determined by the capacity of the processes, or at a rate proportional to the flow in the receiving stream; used to smooth out variations in temperature and composition as well as flow.

equalizing basin  A holding basin in which variations in flow and composition of a liquid are averaged. Such basins are used to provide a flow of reasonably uniform volume and composition to a treatment unit. Also called balancing reservoir.

equilibrium  A condition of balance in which the rate of formation and the rate of consumption or degradation of various constituents are equal. See also chemical equilibrium.

equilibrium constant  A value that describes the quantitative relationship between chemical species in a system at equilibrium.

equivalent calcium carbonate  A common form of expressing hardness, the acidity, or the carbon dioxide, carbonate, bicarbonate, noncarbonate, hydroxide, or total alkalinity of water; expressed in milligrams per liter (mg/L). It is calculated by multiplying the number of chemical equivalents of any of these constituents present in 1 L by 50, the equivalent weight of calcium carbonate. See also chemical equivalent.

Escherichia coli (E. coli)  One of the species of bacteria in the fecal coliform group. It is found in large numbers in the gastrointestinal tract and feces of warm-blooded animals and man. Its presence is considered indicative of fresh fecal contamination, and it is used as an indicator organism for the presence of less easily detected pathogenic bacteria.

eutrophication  Nutrient enrichment of a lake or other water body, typically characterized by increased growth of planktonic algae and rooted plants. It can be accelerated by wastewater discharges and polluted runoff.

evaporation  (1) The process by which water becomes a vapor. (2) The quantity of water that is evaporated; the rate is expressed in depth of water, measured as liquid water removed from a specified surface per unit of time, generally in inches or centimeters per day, month, or year. (3) The concentration of dissolved solids by driving off water through the application of heat.

evaporation opportunity  The ratio of the rate of evaporation from a land or water surface in contact with the atmosphere to evaporation under existing atmospheric conditions; that is, the ratio of the actual to the potential rate of evaporation. Also called relative evaporation.

evaporation rate  The quantity of water, expressed in terms of depth of liquid water, evaporated from a given water surface per unit of time. It is usually expressed in inches or millimeters per day, month, or year.

evapotranspiration  Water withdrawn from soil by evaporation or plant transpiration; considered synonymous with consumptive use.

evapotranspiration potential  Water loss that would occur if there was never a deficiency of water in the soil for use by vegetation.

explosimeter  A device for measuring the concentration of potentially explosive fumes. Also called a combustible-gas indicator.

extended aeration  A modification of the activated-sludge process using long aeration periods to promote aerobic digestion of the biological mass by endogenous respiration. The process includes stabilization of organic matter under aerobic conditions and disposal of the gaseous end products into the air. Effluent contains finely divided suspended matter and soluble matter.

extended aeration process  A modification of the activated-sludge process. See extended aeration.

extraction  The process of dissolving and separating out particular constituents of a liquid by treatment with solvents specific for those constituents. Extraction may be liquid–solid or liquid–liquid.