TM 5-813-8
A suitable tank to meet suck-back requirements will be
-The maximum amount of waste brine that
designed for all membranes that could be damaged by
can be economically disposed of may
dehydration. The system design must be based on
place a limitation on the raw water used in
equipment with a history of successful water treatment
the process.
experience. The required experience should include a
-Availability of the raw water may limit the
minimum of 2 years of experience, treatment capacity,
raw water used in the process.
repair frequency and duration, and a ratio of repair cost
The principle requirement in a reverse osmosis design is
to capital cost.
The requirement for successful
an accurate projection of the chemical, biological, and
experience will limit the amount of untested innovation
physical makeup of the poorest quality water that will
used at a facility. When a particular metallurgy or
ever be used as raw feed water at the site being
material is required for strategic, corrosion design, or
investigated. The design documentation must include
process economic reasons, this metallurgy will be
the following:
included for all applicable parts and spare parts and
-Maximum total dissolved solids.
equipment.
-Maximum concentration of every ion that
could precipitate or influence the activity
coefficient of a precipitation reaction.
7-6.
Materials of construction.
(See App. B.)
Ferric ions will cause severe problems in membrane
-Maximum concentration of each ion that
systems. For this reason, never permit carbon steel to
must be controlled in the product water.
be in contact with the feed water being supplied to a
-Concentration of both molybdate reactive
membrane desalination plant. Use nylon or other
and molybdate nonreactive silica.
plastics capable of maintaining the desired pressures
-Maximum allowable concentration of
whenever possible. Use 316L stainless steel for pump
nonionizable material.
impellers and other feed-water-contact metal surfaces if
-An oil and grease analysis to levels below
hexametaphosphate is used for scale control. If no
10 milligrams per liter.
scale inhibition is necessary, use bronze for pump
-Any gas or potential corrosive agent that
impellers.
may be in the feed water.
d. Process design. When a particular membrane
has been identified as the most economic, the design
will be limited to the one membrane type. The process
design for any reverse osmosis process will consider
raw water quality and the required final product water
quality.
7-13
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