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Home>Water University>Water Glossary>Water Glossary: E

Water Glossary: E


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E. Coli The common abbreviation of Escherichia Coli.
Eductor A device utilizing a nozzle and throat, installed in a stream of water to create a partial vacuum to draw air or liquid into the stream; commonly used to draw regeneration chemicals into an ion exchange water treatment system, such a softener or deionizer.
Effective Size A measure of the size of particles of ion exchanger or filter medium; defined as the diameter of a specific particle in a bed, batch or lot which has 10 percent smaller and 90 percent larger particles.
Efficiency The ratio of output per unit input or the effectiveness of performance of a system; in an ion exchange system, often expressed as the amount of regenerant required to produce a unit of capacity, such as the pounds of salt per kilograin of hardness removal.
Effluent The stream emerging from a unit, system or process, such as the softened water from an ion exchange softener.
Ejector A device which used a high velocity jet to entrain a gas or liquid in a stream of air or liquid. (See eductor.)
Electrodialysis A process in which a direct current is applied to a cell to draw charged ions through ion selective semipermeable membranes, thus removing the ions from the solution.
Electrolysis In general, the chemical change caused by the passage of an electric current, often a decomposition of a material; the decomposition of water into oxygen and hydrogen by the application of a direct current; the action in which one metal goes into solution in a galvanic cell at the junction between dissimilar metals in a water system. (See galvanic corrosion.)
Electrolyte A nonmetallic substance that carries an electric current, or a substance which, when dissolved in water, separates into ions which can carry an electric current. (See conductance, ionization.)
Electron A fundamental particle found in the atom which carries a single negative charge.
Elution The stripping of ions from an ion exchange material by other ions, either because of greater affinity or because of much higher concentration.
Endpoint The point at which a process is stopped because a predetermined value of a measurable variable is reached.
Equilibrium The state in which the action of multiple forces produce a stead balance.
Equilibrium Reaction A chemical reaction which proceeds primarily in one direction until the concentrations of reactants and products reach an equilibrium.
Equivalent Weight The weight in grams of an element, compound or ion which would react with or replace 1 gram of hydrogen; the molecular weight in grams divided by the valence.
Erosion The process in which material is worn away by a stream of air or liquid, often due to the presence of abrasive particles in the stream; a physical or mechanical wearing process rather than a chemical solution process.
Escherichia Coli One of the members of the coliform groups of bacteria indicating fecal contamination. (See fecal, coliform.)
Exchange Velocity The rate with which one ion is displaced from an ion exchange material in exchange for another ion.
Exemption State or EPA permission for a water system not to meet a certain drinking water standard. An exemption allows a system additional time to obtain financial assistance or make improvements in order to come into compliance with the standard. The system must prove that: (1) there are compelling reasons (including economic factors) why it cannot meet a MCL or Treatment Technique; (2) it was in operation on the effective date of the requirement, and (3) the exemption will not create an unreasonable risk to public health. The state must set a schedule under which the water system will comply with the standard for which it received an exemption.
Exhaustion The state of an ion exchange material that is no longer capable of effective function due to the depletion of the initial supply of exchangeable ions. (See ion exchange, endpoint.)
Exposure Contact between a person and a chemical. Exposures are calculated as the amount of chemical available for absorption by a person.