5 Design Considerations for Industrial Reverse Osmosis

5Design Considerations for
Industrial Reverse Osmosis
INDUSTRIAL WATER FILTRATION
800.999.4195
www.WaterProfessionals.com info@waterprofessionals.com

Introduction:
• Reverse osmosis (RO) is one of the
most cost effective methods of treating:
– Boiler feedwater,
– Cooling tower makeup water, and
– Industrial process water.
800.999.4195

• Reverse osmosis may also be used to produce demineralized
water, negating the need to handle and dispose of hazardous chemicals.
• Through technological advancements, reverse osmosis systems have
become capable of economically filtering:
– Boiler feedwater,
– Cooling tower makeup water and
– Process water at virtually any required flow.
800.999.4195

• For an industrial RO system to operate at maximum efficiency,
several factors must be taken into consideration during the design
process.
1. Water Source
2. Temperature and Flow Rate
3. Pretreatment
4. Microbiological Contaminants
5. Silt Density Index
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1. Water Source
• The source of feedwater for an RO system has one of the greatest impacts
on the overall design of the unit, including the number of required
filtration stages for pretreatment.
– Water from a source that is stable in composition and temperature, such as a
groundwater supply, will typically require a simpler pretreatment process.
– Water from a seasonal water source, such as surface water, will require a more complex
pretreatment process.
800.999.4195

• Feedwater must typically be pretreated to remove contaminants that
would scale or foul the membranes in a reverse osmosis system.
• Cutting edge membrane technologies, combined with advancements in
antiscalant chemistry, have vastly reduced pretreatment capital cost over
the past decade.
800.999.4195

2. Temperature and Flow Rate
• The flux rate, or rate at which water passes through a membrane, varies
markedly with water temperature.
• Warm water will flow much quicker through the membrane of a reverse
osmosis system than cold water.
• For this reason, a variable frequency drive (VFD) is frequently specified on
larger RO systems to maintain constant flow regardless of water temperature.
800.999.4195

• Most industrial reverse osmosis
systems are rated by the factory
to treat water at an ideal
temperature of 77° Fahrenheit.
• Water temperature and flow
rate parameters must be taken
into consideration during the
design of a reverse osmosis
system and pretreatment
equipment.
800.999.4195

• The coldest potential feedwater temperature must be
determined and the reverse osmosis system size selected
accordingly.
• If applied without taking into account actual operating
temperature, especially during winter, reverse osmosis output
will drop below design specifications.
800.999.4195

3. Pretreatment
• Chlorine, while beneficial for disinfecting municipal water, will deteriorate
reverse osmosis membranes.
• Dechlorination is achieved by activated carbon filtration of reverse
osmosis feedwater treated with a chlorine reducing agent, like sodium
bisulfite, as part of the pretreatment process.
800.999.4195

• To prevent scaling from calcium and
magnesium carbonates, feedwater should be
pretreated with a cation exchange water
softener or chemical antiscalant, depending
on the water hardness level.
800.999.4195

4. Microbiological Contaminants
• Although not generally as damaging as scaling,
microbiological contaminants trapped in the
membrane of a reverse osmosis system can also result
in fouling and a loss of production capacity.
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• Pretreatment is important when working with RO and
nanofiltration (NF) membranes due to the nature of their
spiral wound design, which only allows water to flow one-way
through the system.
• A biocide may need to be added to feedwater to control
microbiological growth.
800.999.4195

5. Silt Density Index
• Significant levels of very fine particles (i.e., silt) in water can result in frequent
membrane cleanings, or even premature membrane failure.
• To prevent a loss of efficiency and down time, feedwater should be evaluated using a
silt density index test (SDI) in the field prior to designing pre-treatment for reverse
osmosis systems.
800.999.4195

• Treatment with flocculent upstream of multimedia filtration may be
required for feedwater that contains significant levels of silt.
• However, care must be exercised in selecting the flocculent and
establishing the correct dosage since many such compounds will
irreversibly foul the membranes.
• In some cases, membrane-based micro or ultrafiltration is required based
on particle size distribution (carried out by laboratory testing) or total
suspended solids (TSS).
800.999.4195

About WaterProfessionals®
• WaterProfessionals® specializes in providing custom engineered reverse
osmosis systems to meet a variety of industrial and commercial needs.
• For assistance in selecting the right reverse osmosis and water filtration
system for your industrial application, visit:
http://www.WaterProfessionals.com
800.999.4195

Contact WaterProfessionals® Today:
800.999.4195
info@waterprofessionals.com
Or Visit: www.WaterProfessioinals.com

5 Design Considerations for Industrial Reverse Osmosis

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5 Design Considerations for Industrial Reverse Osmosis