Efficiency - the ratio of output per unit input; 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 kilogram of hardness removal.
Electrodialis - a process in which a direct current is applied to a cell to draw charged ions through ion selective semipermiable membranes, thus removing the ions from the solution.
Endpoint - the point at which a process is stopped because a predetermined value of a measurable variable is reached, the endpoint of an ion exchanger water softener service run is the point at which the hardness of the softener effluent increases to a predefined concentration, often 1.0 grain per gallon; the endpoint of a filter service run may be the point at which the pressure drop across the filter reaches a predetermined value; the endpoint of a titration is the point at which the titrant produces a predetermined color change, ph value, or other measurable characteristic.
Equivalent Per Million - a unit of concentration used in chemical calculations, calculated by dividing the concentration in ppm or mg/1 by the equivalent weight.
Exhaustion - the state of an ion exchange material in which it is no longer capable of effective function due to the depletion of the initial supply of exchangeable ions; the exhaustion point may be defined in terms of a limiting concentration of matter in the effluent, or in the case of demineralization, in terms of electrical conductivity.