SNOWPURE, LLC, 2005-2018
VERSION 3.5 (XL+EXL)
–FEBRUARY 2018
PAGE 39
Rules of thumb: If the RO permeate (feed to the EDI) is 1-5
μS/cm, operation
can continue with no problem. If the RO permeate is under 1 μS/cm, some
special system configurations might be considered. The goal for the
concentrate outlet should be ideally 10-10
0 μS/cm. A mass balance on the
system can be used to calculate the concentrate outlet based on the recovery
and the inlet concentrations.
In order to optimize the design of a 2-pass RO-EDI system
with less than 1 μS/cm, there
are several system design options:
1. Feed the concentrate and electrode streams with permeate from the 1
st
pass RO
(e.g., > 5
μS/cm). Or, feed the concentrate and electrode streams with
concentrate from the 2
nd
pass RO (e.g., > 1
0 μS/cm). The choice of which
depends on the conductivities of each, and the concentrations of the impurity
ions in each.
2. Inject NaCl brine (good salt
8
) into the concentrate/electrode streams to a level
around 10-100
μS/cm based on achieving 40-100 μS/cm in the concentrate
outlet
—this is generally not an ideal system because of maintenance costs.
3. Circulate the concentrate stream with a feed-and-bleed system. This is not
recommended since NaCl injection is simpler and better, and avoids buildup of
hard ions which results in scaling, and concentrate recirculation may also lead to
bacteria outbreaks in the loop.
4. Remove the 2
nd
RO pass entirely, or install it in parallel with the 1
st
RO pass to
increase capacity (RO-EDI).
5. Install the 2
nd
RO pass after the EDI as a final membrane barrier in USP24 water-
for-injection applications (RO-EDI-RO).
Installation Notes
Safety
Please read and understand the Safety Section of this manual before installation.
Please
train your colleagues
regarding the safe design and operation of EDI modules.
Key safety topics are the use of electricity around water, and the handling of the gases
produced at the electrodes.
Handling the Module
The module is designed to be compact and lightweight. Care should be taken when
lifting and moving the EDI modules, based on the weight of the module, mechanical
assistance may be required to move the module.
Do not lift by the plumbing or electrical connections
.
Do not lift by the end covers
.
On the XL modules here are 4 lifting points in the aluminum plates on the top of the
module. Two are located on each aluminum plate. A small, screw-pin or safety-pin
shackle with a pin diameter of ¼” (6mm) may be used to lift the module. Ensure that
when lifting the module that there is at least one lift point used on each aluminum plate.
8
If NaCl brine is used, it must be of the highest quality and must have few impurities. Iron and silt are present in cheap
“rock salt”, which must be avoided. Often “silica” is added to “salt” to allow the crystals to “flow”. These can be harmful
to the EDI module over time.