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Advanced
Membrane
Technologies |
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| Advanced
Electrodeionization (AEDI) |
DESCRIPTION
 Advanced
Advanced Electrodeionization (AEDI) devices remove ionizable constituents from water using ion exchange membranes, ion exchange resins, and a DC electrical potential. AEDI provides two technologies in one module: electrodialysis and ion exchange. Ion exchange membranes separate an ion exchange mixed bed from electrodes. The ion exchange resins remove ionic matter from process water, the electrodes provide electro-regeneration of the resin when energized by a DC rectifier.
APPLICATIONS
Exergy’s AEDI system provides superior separation of ionic process
solutions from wastewater and process water. AEDI applications
include:
▪ Direct recovery of electrolytes from active rinses
▪ Recovery and recycling of process water
and wastewater in
industrial applications
BENEFITS
▪ Compact and space saving skids
▪ Separation of water and chemicals
▪ “One-step operation”
▪ Continuous water purification
▪ No chemicals used for regeneration
FEATURES
▪ Clean (electrochemical) technology
▪ Low maintenance
▪ High recovery rate
▪ Low total dissolved solids (TDS) product water
▪ Cost-effective water purification
▪ Option to recycle chemicals
▪ Custom designed for special operations
TECHNOLOGY FEATURES
The AEDI modules are designed and built to ensure the purification
of low TDS process water instead of using a mixed-bed filter.
A TDS reduction to more than 99% can be accomplished with a standard
AEDI skid. For the continuous rinsing of the AEDI module, conductive
process water can be used and recirculated, so that no additional
wastewater is generated.
The resulting effluent from the AEDI rinsing is a low TDS liquid/gas
mixture and the gas coming from the electrodes must be bled into the
atmosphere. The described process provides a yield of 100% for the
AEDI.
The energy requirement for the different AEDI modules is 0.8 to 1.6
kWh/1,000 gallons of high-purity water. This depends on various
process parameters such as process water quality, AEDI rinse feed
quality and temperature. The applied DC voltage is normally between
100 and 300V depending on the type of the modules. The modules are
connected electrically in parallel mode in order to keep the voltage
as low as possible, independent from the system capacity (gpm).
The quality of the water produced by AEDI depends on the process
water quality. The specific resistivity of the purified water from
process water with <12 ppm TDS quality or less than 20 S/cm at
nominal capacity is almost 18.2 megaohm-cm. The diluate quality is
only influenced at higher permeate conductivity.
DETAILED PROCESS DESCRIPTION
There are two distinct operating areas for AEDI devices: enhanced
transfer and electro-regeneration.
In the enhanced transfer area, the resins within the device remain
in the salt forms. In this area, the transport mechanism is ion
exchange on the resin surfaces.
The second operating area for AEDI devices is known as the
electro-regeneration area. This area is characterized by the
continuous regeneration of resins by electrically induced
water-splitting reactions. The resins are “regenerated” to their
hydrogen and hydroxide forms and this allows AEDI devices to
transport compounds that ionize at pH values different from that of
the water to be purified.
The AEDI devices operating in the electro-regeneration area can
remove weakly ionized compounds by internally creating conditions
favorable to ionization reactions. For AEDI mixed-bed devices, the
primary objective of operating in the electro-regeneration area is
to remove weakly ionized compounds, such as carbonic and silicic
acids, and to remove weakly ionized organic compounds. In the
electro-regeneration area, the resins in the ion depleting
compartments remain conductive either because they are in the
regenerated ionic forms, or because the solutes entering them that
are relatively nonconductive in the water become conductive under
the pH conditions within the resin beads.
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