SNOWPURE, LLC, 2005-2018
VERSION 3.5 (XL+EXL)
–FEBRUARY 2018
PAGE 13
DC potential
: voltage that does not change polarity. Electrodeionization is only possible
with this form of driving force. There will be some AC component to the DC voltage.
Electrode
: a metal plate (anode or cathode) that conducts an electrical field and
catalyzes electrochemical reactions. Electrodes are connected directly to a power
supply via a 3-wire connection.
Electrode Stream
: a stream of water that emanates from the electrodes, and includes
ions and electrochemical byproducts. The Electropure technology uniquely combines
both electrode streams in series. This waste stream is small, about 10 l/h.
Feed water
: the water that is plumbed into the EDI module, typically RO permeate. It
supplies the product compartments, concentrating compartments, and electrode stream.
GPM (gpm
): abbreviation for gallons per minute; a measurement for the flow of water,
where 1.0 gpm is equivalent to 227 liters/hr, and 4.4 gpm is equivalent to 1.0 m
3
/hr.
Ion-exchange Membrane
:
a membrane containing ion-exchange groups that is
selectively permeable to either anions or cations, and is impermeable to water.
Ion-exchange Resin
:
resin beads containing ion-exchange groups that selectively
adsorb either anions or cations.
Megohm
:
(technically, Megohm.cm or M
Ω.cm) the unit of measurement typically used
to quantify the ionic purity of product water produced by a deionization system. It is a
measurement of electrical resistance. Ultrapure water with no impurities may reach
18.24 M
Ω.cm at 25°C.
pH:
the measurement of the concentration of the hydrogen ion (H
). pH values are
expressed as a logarithmic scale from 0 to 14. A value at or near 0 is very acidic, a
value at 7 is neutral, and a value at or near 14 is very basic. The ideal pH feed to an
EDI is 7.0-7.5.
Polarization
: the splitting of water molecules into H
and OH
ions with an electrical
current. This will occur when relatively few ions are present in the diluting compartments
and the applied voltage is excessive, causing water to dissociate in order to conduct
current. Fluctuation of pH in the module is typically associated with polarization.
Polarization of water regenerates the ion-exchange resins.
ppb
: parts per billion, or
μg/liter. A unit used to quantify very low levels of specific ions of
interest, such as silica, in high-purity produced water.
ppm
: parts per million, or mg/liter. The unit used to identify the total dissolved solids
(TDS) in water, and is typically used to quantify the purity of feed water entering the EDI
module. At low conductivity, 1 ppm = ~ 2 microsiemens/cm.
Product (Purified) Stream
: the flow of water through the purifying compartments. This
is where deionization occurs. This was formerly known as the Dilute Stream.