• TABLE OF CONTENTS
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 Front Cover
 Title Page
 Table of Contents
 Introduction
 Thermal desalination processes
 Membrane technology
 Multi-stage flash vs. seawater...
 Multi-stage flash vs. seawater...
 Regulations and conclusions and...
 References






Group Title: Special publication - St. Johns River Water Management District; SJ2004-SP7
Title: Technical Memorandum B.7 Demineralization Treatment Technologies
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 Material Information
Title: Technical Memorandum B.7 Demineralization Treatment Technologies
Series Title: Special publication - St. Johns River Water Management District; SJ2004-SP7
Alternate Title: Demineralization treatment technologies for the seawater demineralization feasibility investigation
Physical Description: Book
Creator: R.W. Beck, Inc.
Publisher: St. Johns River Water Management District
Publication Date: 2002
 Subjects
Subject: Saline water conversion
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Bibliographic ID: WC05046188
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.

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Table of Contents
    Front Cover
        Front Cover 1
    Title Page
        Title Page
    Table of Contents
        Table of Contents
    Introduction
        Page 1
        Page 2
        Page 3
    Thermal desalination processes
        Page 4
        Page 3
        Page 5
    Membrane technology
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
    Multi-stage flash vs. seawater reverse osmosis
        Page 12
        Page 11
    Multi-stage flash vs. seawater reverse osmosis
        Page 12
        Page 13
    Regulations and conclusions and recommendations
        Page 14
        Page 15
    References
        Page 16
Full Text














Special Publication SJ2004-SP7

Demineralization
Treatment
Technologies

for the
Seawater Demineralization
Feasibility Investigation
















Technical Memorandum B.7
Demineralization Treatment Technologies



For the



Seawater Demineralization Feasibility Investigation
Contract #SE459AA

by


R. W. Beck, Inc.
800 North Magnolia Avenue, Suite 300
Orlando, Florida 32803-3274





FINAL


St. Johns River Water Management District
P.O. Box 1429
Highway 100 West
Palatka, Florida


December 31, 2002






Contents


Contents

1.0 INTRODUCTION
1.1 G general ........................................................................................................... 1
1.2 Purpose.................................................................................................................. 1
1.3 Early Desalination Technologies............................................................. 2
2.0 THERMAL DESALINATION PROCESSES............................................... 3
2.1 H history ...... ........................ ................................................................................... 3
2.2 Multi-stage Flash Distillation................................................................ 4
2.3 Multi-effect Distillation............................................................................ 4
2.4 Vapor Compression.................................................................................. 5
2.5 Thermal Plant Performance Enhancements............... ....................... 5
3.0 MEMBRANE TECHNOLOGY................................................................................. 6
3.1 G general ........................................................................................................... 6
3.2 Electrodialysis........................................................................................... 6
3.3 Reverse Osmosis Membranes.................................................................. 7
3.3.1 History .............................................................. ................................. 7
3.3.2 Pretreatment Systems ...................................................................... 8
3.3.3 Current Membrane Systems ............................................. .............. 8
3.4 Membrane System Improvements................................................................ 9
3.5 Energy Recovery Systems............................................... .................... 10
4.0 MULTI-STAGE FLASH VS. SEAWATER REVERSE OSMOSIS .......... 11
5.0 HYBRID SYSTEMS ............................................................. 12
6.0 NEW CONCEPTS....................................................................................... 12
7.0 R EG U LA TIO N S ................................................................................................. 14
8.0 CONCLUSIONS AND RECOMMENDATIONS........................................... 14
9.0 R EFER EN C ES .................................................................................................... 16

List of Tables

Table 1 Desalination Technologies .......................................................................... 3
Table 2 Membrane System Performance ................................................................ 9

List of Illustrations

Illustration 1 Multi-stage Flash Distillation Plant........................................ ............ 4
Illustration 2 Electrodialysis Cell ............................................................................ 6
Illustration 3 Yuma Reverse Osmosis Plant .............................................. ............ 7
Illustration 4 MegaMagnum Pressure Vessels ......................................... ........... .. 13
Illustration 5 DesalNate 16-inch Reverse Osmosis Element..................................... 13


Seawater Demmeralization Feasibility Investigation Demineralization Technologies Technical Memorandum






Demineralization Technologies Technical Memorandum


1.0 INTRODUCTION
1.1 General

Desalination, or demineralization is a treatment process that removes salt and
other minerals from brackish water and seawater to produce high quality drinking
water. Various desalination technologies have been in practice for more than 50
years, with nearly 1500 facilities worldwide, according the International
Desalination Association (IDA). Geographically, the greatest number of
desalination facilities is in the Middle East, followed by the US for the second
greatest number of desal plants. There are also desalination facilities in North
Africa, Singapore, Spain, Thailand, Mexico and the Caribbean Islands. The
application of desalination processes has been essential to improve the livability
in these parts of the world. The first desalination plant in the US was installed in
the Florida Keys in the early 1970s, using brackish groundwater demineralization
technologies.

Today, there are more than 50 brackish water demineralization systems in Florida,
with hundreds more located in California. Due to concerns over continued
population growth and depletion of our nation's water resources, finding
alternative drinking water sources has been a problem faced by many water utility
companies, municipalities and water management districts. This is especially true
for those in the states with the greatest population growth, such as California,
Florida and Texas. Traditional groundwater and surface water sources have been
over-pumped and are showing signs of environmental stress. Some coastal
regions, particularly in south Florida, have experienced salt-water intrusion into
groundwater supplies causing municipalities to turn to brackish water
demineralization to supplement their traditional water supply systems.

Large seawater desalination plants are also being considered to meet significant
water demands of the larger municipalities. The largest seawater desalination
plant in the US is currently under construction in Tampa Bay. The facility is
expected to be complete in early 2003 and will initially produce 25 million
gallons per day (mgd) of drinking water. Other large-scale (25 to 50-mgd)
seawater desalination facilities are currently being planned in southern California
and Texas.

1.2 Purpose

The St. Johns River Water Management District (SJRWMD) is proactively
addressing the water supply needs in the northeast region of Florida, which includes
several counties from Jacksonville to Vero Beach. SJRWMD manages water
resources to ensure their continued availability while maximizing both environmental
and economic benefits.


Seawater Demmeralization Feasibility Investigation Demmneralization Technologies Technical Memorandum






Demineralization Technologies Technical Memorandum


Their objectives are to:

Increase available water supplies and maximize overall water use efficiency to
meet identified existing and future needs;
Minimize damage from flooding, using non-structural approaches where
feasible;
Protect and restore floodplain functions;
Protect and improve surface water quality;
Protect and improve groundwater quality;
Maintain the integrity and functions of water resources and related natural
systems;
Restore degraded water resources and related natural systems to a naturally
functioning condition; and
Ensure proper use of tax and other public revenue by focusing on priorities
that further the District's mission and by maintaining a high level of
organizational efficiency.

The SJRWMD's location is:
St. Johns River Water Management District
P.O. Box 1429
Palatka, Florida 32178-1429
Telephone: (386) 329-4500
www.sjrwmd.com or sjr.state.fl.us

R.W. Beck, and its subconsultants, PB Water and PBS&J, has been contracted by
SJRWMD to investigate the feasibility of constructing seawater demineralization
facilities within this region to meet growing water demands. This technical
memorandum is prepared to provide SJRWMD with information on current
desalination technologies and an update on advancements in the industry.

1.3 Early Desalination Technologies

Most early desalination processes were thermal distillation-type processes, which
were common in the Middle East due to the availability of low cost steam at
power plants. By the 1970s commercial membrane processes were available.
These included electrodialysis (ED) and reverse osmosis (RO). ED was
determined to desalt brackish water more cost-effectively than thermal distillation
processes, which was a breakthrough in the industry at that time. Reverse
osmosis processes were expensive to operate due to the high-energy requirement
of these systems. However, there have been significant improvements to
membrane technologies in the past 10 years, which have made reverse osmosis a
more viable, cost-effective water supply alternative.

The most common desalination technologies that have experienced commercial
success are shown in Table 1. These include thermal processes such as multi-


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Demineralization Technologies Technical Memorandum


stage flash, multi-effect distillation and vapor compression and membrane
processes such as electrodialysis and reverse osmosis.


A brief description of theses processes is provided
with a discussion of system improvements
technologies.


in the following section along
in current demineralization


2.0 THERMAL DESALINATION PROCESSES
2.1 History

The first desalination facilities were thermal processes that use heat to distill
seawater and produce high quality product water. According to various
references, more than 50% of the world's desalination plants are thermal
desalination plants. In a thermal process, water is heated; creating a vapor that is
condensed to form fresh water. Thermal processes are traditionally high-energy
systems and have high operational costs, unless low-cost steam energy is
available. To keep energy requirements down, distillation is usually
accomplished by conducting boiling in multiple successive vessels operating at a
low temperature and low pressure.

A common problem in thermal processes is the formation of a scale inside the
process piping. Hardening of minerals in the seawater, especially calcium sulfate,
forms a scale. Scale is difficult to remove and reduces the efficiency of the
process. Chemicals are often added to reduce scale precipitation.


Seawater Demieralization Feasibility Investigation Demmeralization Technologies Technical Memorandum


Table 1. Desalination Technologies

Thermal

- Multi-stage Flash Distillation

- Multiple-Effect Distillation

- Vapor Compression

Membrane

- Electrodialysis

- Reverse Osmosis






Demineralization Technologies Technical Memorandum


2.2 Multi-stage Flash Distillation

Most of the thermal plants m the world use a multi-stage flash (MSF) distillation
process (Illustration 1) In MSF,
seawater is heated inside a vessel
Called a brine heater Seawater
that passes through the vessel in
a bank of tubes is condensed and
flows to another vessel or
"stage", where the ambient
pressure is lower, thus causing
the water to boil When heat is
added into this stage, water boills
rapidly and instantly "flashes"
Into steam However, only a
small portion of the water is
Illustration 1. Multi-stage Flash Distillation Plant

converted to steam, depending on the operational pressure MSF plants have been
built since the 1950's and can have up to 25 stages, which makes them costly and
complex to operate Operating the plant at temperatures higher than 110 oF can
increase the system's efficiency, but also increases the formation of scale and
potential corrosion

2.3 Multi-effect Distillation

The first multi-effect distillation (IED) processes were submerged tube
evaporators used aboard ships to produce drinking water and boiler make-up
water during long sea voyages These plants were determined to have more scale
build up than MSF plants and have since decreased in their commercial use The
basic MED process consists of multiple vessels that undergo condensation and
evaporation to produce water, similar to the MSF process However, in the MED
process, the feedwater is added to various stages (or effects) by spraying water
onto heated tubes filled with steam The vapor from the outside of the tubes
passes from the boiling chamber through a wire mesh mist eliminator to a
condensing chamber The mist eliminator coalesces droplets of concentrate in the
vapor stream and returns them to the boiling chamber The remaining vapor is
almost pure water In the condensing chamber, the vapor condenses on the
outside of tubes The product water pump extracts the condensed vapor as
distilled product water In this process, the vapor generated in the first effect
becomes the heating steam in a second effect and so on

The process design uses large temperature differences to enhance the heat transfer
in the submerged tube evaporator The thermal efficiency of the process depends
on the number of effects Lower operating temperatures reduce the potential for
scale formation Therefore, the limited operating temperature range and the large

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Demineralization Technologies Technical Memorandum


stage flash, multi-effect distillation and vapor compression and membrane
processes such as electrodialysis and reverse osmosis.


A brief description of theses processes is provided
with a discussion of system improvements
technologies.


in the following section along
in current demineralization


2.0 THERMAL DESALINATION PROCESSES
2.1 History

The first desalination facilities were thermal processes that use heat to distill
seawater and produce high quality product water. According to various
references, more than 50% of the world's desalination plants are thermal
desalination plants. In a thermal process, water is heated; creating a vapor that is
condensed to form fresh water. Thermal processes are traditionally high-energy
systems and have high operational costs, unless low-cost steam energy is
available. To keep energy requirements down, distillation is usually
accomplished by conducting boiling in multiple successive vessels operating at a
low temperature and low pressure.

A common problem in thermal processes is the formation of a scale inside the
process piping. Hardening of minerals in the seawater, especially calcium sulfate,
forms a scale. Scale is difficult to remove and reduces the efficiency of the
process. Chemicals are often added to reduce scale precipitation.


Seawater Demieralization Feasibility Investigation Demmeralization Technologies Technical Memorandum


Table 1. Desalination Technologies

Thermal

- Multi-stage Flash Distillation

- Multiple-Effect Distillation

- Vapor Compression

Membrane

- Electrodialysis

- Reverse Osmosis






Demineralization Technologies Technical Memorandum


temperature difference required by the submerged tube evaporator process limits
the number of effects that can be used in multi-effect evaporators. Some
improvements to the efficiency of the MED process have led to an increasing
number of these systems commercially; however, the total number of MED
systems is much lower than MSF systems.

2.4 Vapor Compression

Another distillation technology known as vapor compression (VC) is used for
smaller-scale desalination facilities. This process is based on the Carnot
refrigeration cycle, in which a mechanical compressor (rather than a heat source)
is used to compress the vapor from the evaporator to a higher pressure. As the
compressed vapor condenses on one side of the tube heat transfer surface,
seawater boils on the other side creating more vapor. This process uses electric
energy rather than steam. The VC evaporator is more efficient than the
previously described steam driven evaporators, but electric power is significantly
more expensive than steam energy.

VC evaporators operate either at atmospheric pressure (215F) or under a vacuum
(140'F) depending on the design. The lower temperature evaporators must be
larger to accommodate the higher specific volume of water vapor at lower
temperatures. These low temperature units have a reduced tendency to scale or
corrode and require less heat recovery between the feed seawater and the
concentrate and distillate streams.

VC units are commonly used at drilling sites and for some small industries since
they are more compact than other thermal processes and electric power is readily
available. The number of VC units currently in operation is very small (4%
worldwide) as compared to multi-stage flash systems, which are estimated at 44%
worldwide, according to IDA, 1998.

2.5 Thermal Plant Performance Enhancements

The most important advancements in thermal desalination over the past 10 years
have been increasing system efficiency and operational reliability. The
operational enhancements have included scale control improvements, automation
and controls, further operator training and better materials of construction.
Additionally, increases in standard-unit sizes have increased the economies of
scale for larger systems. But still these systems have very high-energy
requirements and can be cost prohibitive unless low cost steam energy is available
from a power plant.







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Demineralization Technologies Technical Memorandum


3.0 MEMBRANE TECHNOLOGY

3.1 General

Desalination through the use of membranes was introduced in the 1960s as an
alternative to distillation. A membrane process is a physical separation process,
where salt is separated from seawater or brackish water to produce drinking
water. These membrane processes include electrodialysis (ED) and reverse
osmosis (RO). These process produce the same result, however, ED uses voltage
to separate the salts, where RO operates under pressure for the separation process.

3.2 Electrodialysis

Electrodialysis was the first membrane process put into commercial application,
even before RO. As mentioned above, ED is a voltage driven process that uses an
electrical current to move salts through the membrane, leaving behind freshwater
that is collected as the product water. ED is common in brackish water
demineralization systems, where most of the dissolved salts are ionic in nature.
The dissolved ions such as chlorides, sodium, calcium and carbonate move to the
electrodes with an opposite electric charge. ED membranes can also achieve
selective passage of either anions or cations. The membranes are arranged with
alternating anion-selective membranes followed by cation-selective membranes.
A spacer channel is placed in between each membrane, one carries feedwater,
while the next carries the concentrate. The spaces bound by the two membranes
are called cells. Each ED unit consists of hundreds of cell pairs, and is called a
membrane stack. An example of and ED system is shown below (Illustration 2.)

















Illustration 2. Electrodialysis Cell

After years of operating ED processes, an electrodialysis reversal (EDR) process
was developed. In an EDR process, the polarity of the electrodes is reversed
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Demineralization Technologies Technical Memorandum


causing the flows in the product and brine channels to be switched. The reversal
process helps to breakup and flush out any scaling material that develops on the
cells, minimizing membrane fouling. The ED and EDR processes have a high
recovery of product water and are capable of treating waters with high-suspended
solids. These systems also have low chemical usage. The required energy is
dependent on the desired salt removal.

3.3 Reverse Osmosis Membranes
3.3.1 History

RO is relatively new as compared to the distillation and ED processes.
The first commercial unit was installed in the Florida Keys in 1971. The
RO membrane separation process separates freshwater from saltwater
under high pressure. The freshwater passes through the membrane layer
while the salt content remains outside the membrane. (This is the opposite
of ED, where the demineralization concentrate passes through the
membrane and the freshwater stream remains outside the membrane and is
collected.) The amount of freshwater produced varies from 30 to 80%
depending on the salt content of the water, pressure and the type of
membranes used. Brackish water membrane systems typically have
higher recoveries and operate under lower pressures, ranging from 225 psi
to 375 psi. Seawater RO systems typically have lower recoveries due to
the higher salt content and their operating range is typically 800 to 1200
psi.

Il aio. The majority of the reverse osmosis
plants in the US are brackish water
-- treatment systems. By the early
-r ae a1980's, the world's largest brackish
water membrane treatment system
S- was installed in Yuma, Arizona
(Illustration 3.) There are more than
50 brackish water systems located in
S- Florida and hundreds more in
California, Arizona, and Texas.


Illustration 3. Yuma Reverse Osmosis Plant

Commercial membranes are available in four configurations: plate-and-
frame, spiral wound, tubular and hollow fiber. The tubular and plate-and-
frame arrangements were the original designs, but have a high capital cost
and a high volume requirement. The hollow fiber membranes are no
longer very common since the primary manufacturers, DuPont and Dow,
have discontinued the product. Currently, the most common commercial
membrane configuration is the spiral-wound element. The original
standard membranes were made of cellulose acetate (CA) and had a life
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Demineralization Technologies Technical Memorandum


expectancy of only 1 year and a salt rejection of 90%. Now, membranes
are typically made of thin-film composite polyamide, which a life
expectancy of up 5 to 7 years and a salt rejection of as high as 99.6%.

3.3.2 Pretreatment Systems

The success of membrane desalination is dependent on the performance of
the membranes. Pretreatment to improve the quality of the feed water is
an important first-step in the overall success of the process. Conventional
pretreatment typically includes a combination of the following processes:
Gravity sand filtration
Flocculation
Settling
Cartridge filtration
Chlorination, ultraviolet irradiation, or ozonation
Dechlorination
Acidification
Anti-scalant dosing
Softening
Activated-carbon-bed filtration
Multi-media filtration
Green sand (Magnesium Hydroxide) filtration
Degasification.

The filtration steps are intended to remove suspended solids, colloids, or
dissolved metals from the feedwater. Chlorination, ultraviolet irradiation
and ozonation are intended to kill algae and prevent biofouling of the
membranes. Sulfuric acid, anti-scalant dosing, and softening reduce the
tendency of the feed water to create scale on the membrane surface.
Degasification is used to remove dissolved gases from the feed such as
carbon dioxide and hydrogen sulfide. The constituents in the raw water
determine the specific pretreatment processes needed for a specific site.
Therefore, a complete chemical analysis of the water source is
recommended prior to design of the system.

Within the last several years, microfiltration (MF) and ultrafiltration (UF)
membrane systems have begun to replace conventional water treatment
processes for the pretreatment of surface water and seawater supplies.
The use of these technologies is projected to extend the life of the
seawater reverse osmosis (SWRO) elements an additional 3 to 5 years.

3.3.3 Current Membrane Systems

Today's membranes are susceptible to damage from chlorine and
temperatures above 450C (113F). Spiral wound elements are subject to
excessive fouling if the feed water contains too high a level of suspended

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Demineralization Technologies Technical Memorandum


solids. Therefore, pretreatment using one of the above-described
pretreatment methods is essential. Plugging tendency is measured in units
of silting density index (SDI). Membranes typically require an SDI of 5 or
less.

The key performance parameters for RO are permeate (or product water)
flux and salt rejection. The permeate flux is the flow rate of water through
the membrane per unit area, usually expressed as gallons per day per
square foot. The salt rejection is expressed in terms of a percentage and is
the ratio of the concentration of the salt in the product water divided by the
concentration of the salt in the feed water. Permeate flux and salt rejection
are impacted by operating pressure, temperature, product water recovery
and feedwater salt concentration. Recovery is the amount or percentage of
product water that can be produced from the feedwater flow. The key
membrane system performance trends are described in Table 2.

Table 2. Membrane System Performance

As Operating Pressure Increases Flux Increases and Salt Rejection
Increases
As Recovery Increases Flux Decreases and Salt Rejection
Decreases
As Temperature Increases Flux Increases and Salt Rejection
Decreases
As Salinity in Feedwater Increases Flux Decreases and Salt Rejection
Decreases

RO membranes work best when provided with a consistent feed water
quality. However, in most applications the feed water quality varies either
hourly, daily or seasonally. As feed water quality varies, plant operation
must be altered to obtain optimum performance. While computer
controlled operating programs can handle expected variations, trained
operators must be available to handle unexpected variations and
equipment failures along with periodic maintenance. Membranes are still
a fragile component that can be ruined in less than an hour by incorrect
operation. In addition to monitoring plant operation, operators must
regularly refill chemical dosing day tanks, replace cartridge filters,
monitor plants for leaks and rotating equipment for unusual sounds, and
periodically perform chemical cleaning of membranes.

3.4 Membrane System Improvements

Many advances in membrane technology have occurred since membranes were
first developed. The most significant improvements have occurred in the last 10
years. These improvements have included the development of more efficient
membranes that can operate at higher temperatures, have higher salt rejection, and

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Demineralization Technologies Technical Memorandum


greater product water recoveries. Membranes now have higher flux rates (flow
rate per unit area), lower fouling potential, lower costs and longer lives than ever
before. Manufacturing plants have implemented automated systems, which have
improved production and quality control resulting in lower element costs. The
cost of membrane elements has been reduced from more than $750 per element to
$400 to $450 per element. This trend may continue with further membrane
system advancements.

Another industry improvement has consisted of the development of nanofiltration
(NF) membranes for water softening. NF membranes have a much lower
rejection of chlorides than RO membranes. However, NF operates at lower
pressures and has a higher percentage of product water recovery as compared to
RO. Using NF or other membrane systems such as microfiltration or
ultrafiltration as a pretreatment to distillation or RO has driven the desalination
industry away from chemical pretreatment processes and more toward all-
membrane treatment systems.

Additionally, there have been advancements in energy recovery devices. The new
devices now have greater efficiencies, which result in more energy recovery and
lower operational costs. These improvements in both membrane technology and
energy recovery have yielded significant reductions in desalination system capital
and operational costs.

3.5 Energy Recovery Systems

Energy recovery is now a key component of membrane desalination processes.
This has been a significant improvement in the desalination industry. Because
seawater RO operates at pressures from up to 1200 psig, significant energy is
required for the process. Energy recovery devices recover most of this energy and
transfer it to the feedwater to reduce the overall process energy requirements.
Typical devices and efficiencies consist of reverse running pumps (70%
efficiency), turbines (77% efficiency), Pelton wheel turbines (83% efficiency),
and work exchangers (90% efficiency). In addition, pump manufacturers are
designing large centrifugal pumps with efficiencies approaching the efficiency of
positive displacement pumps of 90% as compared to previously typical
efficiencies of 70%. With optimum design, energy usage as low as 11.4
kWh/kgal is now reported possible, where typical electrical consumption by the
high-pressure pumps has been 16 kWh/Kgal historically.

Of the proven, commercialized energy recovery technologies, the positive
displacement technologies such as the ERI Pressure Exchanger and Desalco Work
Exchanger appear to be most efficient.

There are also new emerging energy recovery devices such as the Vari-RO Direct
Drive (DDE), Vari-RO ISB and IPER systems recently tested by the United States
Bureau of Reclamation. The Vari-RO energy recovery systems appear to be


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Demineralization Technologies Technical Memorandum


technically viable systems, but have not yet been used in a full-scale commercial
application.

Energy recovery is a very important component of the overall desalination facility
since it can help reduce energy requirements and the operating costs of a
desalination facility. Therefore, continued monitoring of most efficient energy
recovery systems is important to the desalination facility design.

4.0 MULTI-STAGE FLASH VS. SEAWATER REVERSE OSMOSIS

Although there have been many desalting technologies tested over the years, RO and
thermal processes have had the greatest commercial success. Based on available
literature, the total number of RO facilities (both brackish and seawater RO) at nearly
40% of all demineralization facilities. The total number of thermal plants in the world is
slightly greater than 50% (IDA, 1998). The choice between multi-stage flash and
seawater RO needs to be based on a number of site-specific factors. The inherent
advantage of RO is that it has much higher energy efficiency. Since the cost of energy is
usually the major cost of producing water, RO will usually be preferred, but some factors
may overrule this.

First is the feed water quality. As the total dissolved solids (TDS) concentration in the
seawater increases, RO becomes more costly because of the increased osmotic pressure
required to separate the salts. Additionally, if the source water is high in suspended
solids, colloidal material, organic material, or dissolved metals, it would require
extensive pretreatment if RO was used. This could be cost prohibitive in some cases.

The second factor that influences the choice of MSF vs. RO is the availability of low cost
energy. If there is an abundance of low cost steam available to operate the desalination
plant, the energy-efficiency advantage of RO becomes less important. This can be seen
in a dual-purpose power and water plant (or co-generation facility) where exhaust steam
from the power plant is used to operate a desalination plant to produce high quality water.

One last factor to consider is the availability of skilled operators. While skilled operators
are important for both MSF and RO plants, the relative fragility of RO membranes
requires more skillful attention by the operators to protect the investment cost of the RO
plant. MSF evaporators are relatively hardy and can usually be restored in spite of
negligent operation.


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Demineralization Technologies Technical Memorandum



5.0 HYBRID SYSTEMS

Hybrid systems use a combination of two or more desalination processes. These systems
usually are combined with the intent to obtain some advantage over either process alone.
The advantage may be improved efficiency or reduced feedwater flows, which in turn
result in lower costs, or possibly better product water quality. The disadvantage of hybrid
systems is that they are typically more complex to operate. An example of a hybrid
system is a "membrane distillation" process that uses membranes to separate salty water
from fresh water and uses evaporation to transport the fresh water from the membrane
surface. Membrane distillation processes claim to have high efficiencies, but they have
not yet been commercially proven.

6.0 NEW CONCEPTS

There are new emerging desalination technologies in the development stages that will
likely revolutionize the desalting industry once proven and put into commercial
application. An example of such emerging technologies currently being developed is
described in a new, Department of Energy (DOE)-sponsored project entitled "A Modified
Reverse Osmosis System for Treatment of Produced Water", New Mexico Research and
Economic Development, 2001. Scientists developing this water treatment system claim
that they can economically demineralize water, produce a solid salt waste, and yield
100% water recovery. In June 2000, the proposed project was awarded $1.2 million from
the DOE, with 25% matching funds from New Mexico Tech.

Similarly, AquaSonics has developed a "Rapid Spray EvaporationTM (RSE) system",
which is based on the principle that saltwater can be ejected at such high velocities that,
as rapid evaporation occurs, solids separate out and are trapped. The resulting vapor is
condensed into pure water. According to AquaSonics, the added benefit of the RSE
process is that the demineralization concentrate is evaporated and the salt precipitates out
as a solid and remains crystalline, which reduces controversial and costly concentrate
disposal options. The salt product is said to be a commercially viable raw material.
Based on information provided by AquaSonics, the RSE is claimed to achieve in one step
what RO and MSF require in four or more steps and have a 95% recovery of fresh water
as compared to 40% achieved by RO and MSF on seawater. In essence, the Aquasonics
RSE is alleged to require one-fourth the capital investment and supposedly generates
three times the volume of fresh water for the same, or less energy input as compared to
MSF at 30 kwh/m3 (or 113.4kWh/1,000 gallons). However, it should be noted that this
is still significantly more energy use than reverse osmosis systems. The claims that
Aquasonics makes are interesting, but still need to be proven viable at a commercial-
scale.

Another emerging improvement in desalination is the development of larger RO
membrane elements to make the process more efficient and improving the economies of
scale. Recently, Koch Membrane Systems, Inc. has introduced the world's largest reverse
osmosis element, the Fluid Systems MegaMagnum (Illustration 4).

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Demineralization Technologies Technical Memorandum


technically viable systems, but have not yet been used in a full-scale commercial
application.

Energy recovery is a very important component of the overall desalination facility
since it can help reduce energy requirements and the operating costs of a
desalination facility. Therefore, continued monitoring of most efficient energy
recovery systems is important to the desalination facility design.

4.0 MULTI-STAGE FLASH VS. SEAWATER REVERSE OSMOSIS

Although there have been many desalting technologies tested over the years, RO and
thermal processes have had the greatest commercial success. Based on available
literature, the total number of RO facilities (both brackish and seawater RO) at nearly
40% of all demineralization facilities. The total number of thermal plants in the world is
slightly greater than 50% (IDA, 1998). The choice between multi-stage flash and
seawater RO needs to be based on a number of site-specific factors. The inherent
advantage of RO is that it has much higher energy efficiency. Since the cost of energy is
usually the major cost of producing water, RO will usually be preferred, but some factors
may overrule this.

First is the feed water quality. As the total dissolved solids (TDS) concentration in the
seawater increases, RO becomes more costly because of the increased osmotic pressure
required to separate the salts. Additionally, if the source water is high in suspended
solids, colloidal material, organic material, or dissolved metals, it would require
extensive pretreatment if RO was used. This could be cost prohibitive in some cases.

The second factor that influences the choice of MSF vs. RO is the availability of low cost
energy. If there is an abundance of low cost steam available to operate the desalination
plant, the energy-efficiency advantage of RO becomes less important. This can be seen
in a dual-purpose power and water plant (or co-generation facility) where exhaust steam
from the power plant is used to operate a desalination plant to produce high quality water.

One last factor to consider is the availability of skilled operators. While skilled operators
are important for both MSF and RO plants, the relative fragility of RO membranes
requires more skillful attention by the operators to protect the investment cost of the RO
plant. MSF evaporators are relatively hardy and can usually be restored in spite of
negligent operation.


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5.0 HYBRID SYSTEMS

Hybrid systems use a combination of two or more desalination processes. These systems
usually are combined with the intent to obtain some advantage over either process alone.
The advantage may be improved efficiency or reduced feedwater flows, which in turn
result in lower costs, or possibly better product water quality. The disadvantage of hybrid
systems is that they are typically more complex to operate. An example of a hybrid
system is a "membrane distillation" process that uses membranes to separate salty water
from fresh water and uses evaporation to transport the fresh water from the membrane
surface. Membrane distillation processes claim to have high efficiencies, but they have
not yet been commercially proven.

6.0 NEW CONCEPTS

There are new emerging desalination technologies in the development stages that will
likely revolutionize the desalting industry once proven and put into commercial
application. An example of such emerging technologies currently being developed is
described in a new, Department of Energy (DOE)-sponsored project entitled "A Modified
Reverse Osmosis System for Treatment of Produced Water", New Mexico Research and
Economic Development, 2001. Scientists developing this water treatment system claim
that they can economically demineralize water, produce a solid salt waste, and yield
100% water recovery. In June 2000, the proposed project was awarded $1.2 million from
the DOE, with 25% matching funds from New Mexico Tech.

Similarly, AquaSonics has developed a "Rapid Spray EvaporationTM (RSE) system",
which is based on the principle that saltwater can be ejected at such high velocities that,
as rapid evaporation occurs, solids separate out and are trapped. The resulting vapor is
condensed into pure water. According to AquaSonics, the added benefit of the RSE
process is that the demineralization concentrate is evaporated and the salt precipitates out
as a solid and remains crystalline, which reduces controversial and costly concentrate
disposal options. The salt product is said to be a commercially viable raw material.
Based on information provided by AquaSonics, the RSE is claimed to achieve in one step
what RO and MSF require in four or more steps and have a 95% recovery of fresh water
as compared to 40% achieved by RO and MSF on seawater. In essence, the Aquasonics
RSE is alleged to require one-fourth the capital investment and supposedly generates
three times the volume of fresh water for the same, or less energy input as compared to
MSF at 30 kwh/m3 (or 113.4kWh/1,000 gallons). However, it should be noted that this
is still significantly more energy use than reverse osmosis systems. The claims that
Aquasonics makes are interesting, but still need to be proven viable at a commercial-
scale.

Another emerging improvement in desalination is the development of larger RO
membrane elements to make the process more efficient and improving the economies of
scale. Recently, Koch Membrane Systems, Inc. has introduced the world's largest reverse
osmosis element, the Fluid Systems MegaMagnum (Illustration 4).

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Demineralization Technologies Technical Memorandum


The MegaMagnum membrane has a 17-inch
diameter and 60-inch length, having more than
2,400 square feet of membrane surface area.
According to Koch Membrane Systems,
customers can achieve a footprint space-savings
of up to 15 percent, have fewer manifolds and
pressure vessels, and can cut capital costs by
more than 20 percent. The MegaMagnum
element is designed for seawater and brackish
water demineralization applications.

Illustration 4. MegaMagnum Pressure Vessels

Historically, the standard spiral wound element has an 8-inch diameter and length of 40-
inches, yielding up to 440 square feet of membrane surface area. In the 1980s, Fluid
Systems introduced the Magnum, an 8 x 60-inch long element. In recent years, Koch
Membrane Systems has also developed and sold more than 300 15-inch-diameter
elements for various research projects worldwide.

Another firm, NATE-International, is
currently developing the "DesaINATE"
technology. This technology uses 16-inch
diameter membranes compared to the
standard 8-inch diameter. The DesalNATE
process has three channels that feed the
water to membranes in series in a common
pressure vessel.

These large diameter elements are shown in
Illustration 5.

Illustration 5. 16-inch Reverse Osmosis Element

Another new technology by a company called MWD claims to have a unique flow
distributor applying an electro-magnetic field innovation, which prevents foulants from
settling on the membrane surface and clogging the membranes. Unlike conventional RO
systems, this process claims to use no chemical pretreatment, nor any chemicals during
the desalination or membrane cleaning processes.

In summary, the current emerging technologies in desalination are primarily focusing
on today's biggest challenges in desalination: 1) producing a dry salt product from RO
concentrate and 2) producing larger-sized elements such that bigger facilities can be
constructed at lower unit costs (or the cost per 1000 gallons of water produced) to take
advantage of the economy of scale. Many of these advancements are still under study
and have not had full-size commercial application. Should these systems be proven
commercially viable, they will result in significant improvements to the desalination
industry and lower process costs.
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7.0 REGULATIONS

In addition to technology improvements, regulations for better product water quality have
resulted in advancements and additional use of membrane desalination technologies. This
has particularly been seen in the reclaimed water reuse field to further treat wastewater
prior to discharging to surface water or groundwater that may ultimately flow to drinking
water sources. The recently revised drinking water rules by the United States
Environmental Protection Agency (EPA) and the Florida Department of Environmental
Protection (FDEP) have included more stringent requirements regarding cryptosporidium
and Giardia removal and the reduction of disinfection by-products in water treatment
industry. This has resulted in an increased usage of membrane-treatment processes at
surface water treatment plants and on the back-end of wastewater treatment plants to
provide greater removal of the finest of molecules in the water. This has also enhanced
the use of nanofiltration, ultrafiltration and microfiltration systems versus conventional
filtration systems.

8.0 CONCLUSIONS AND RECOMMENDATIONS

Desalination processes has been in use for nearly half a century for desalting brackish and
seawater sources. Most of the world's desalination facilities are thermal (>50%) plants,
with reverse osmosis in second with nearly 40% of the total facilities. However, most of
the RO plants to date are brackish water desalination plants. The first desalination
processes were used in arid regions in the Middle East, followed by Africa, the US and
the Caribbean islands. With depleting drinking water supplies in the coastal areas of the
US, desalination is increasingly being used as an alternative to conventional drinking
water systems, especially where the economics of desalination can favorably compare to
the increased costs of traditional drinking water treatment systems under current
regulations.

While MSF distillation and RO processes are more often used for seawater desalination,
ED and low pressure RO are commonly used for brackish water desalination. The choice
of processes is highly dependent of site-specific conditions. Thermal distillation
processes have mainly been used overseas, where low-cost steam from power plants has
been available. Traditionally, these systems are not as efficient as compared to RO
processes. RO plants utilize electric energy, and can be costly to treat seawater with very
high salinities such as those in the Middle East. The reduced cost of RO systems over the
last 10 years has increased the use of RO for seawater demineralization. These reduced
costs are due to more efficient membranes, greater product water recovery and energy
recovery.

There are several emerging technologies that appear to have potential for significant
advancements in the desalination field. These advancements relate to evaporation of
concentrate to a dry salt for commercial use or disposal, and increased membrane sizes to
improve the economies of scale for larger membrane plants.


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Demineralization Technologies Technical Memorandum


Based on the water supply needs in SJRWMD, the following conclusions and
recommendations are provided for consideration in the feasibility investigation of
demineralization on the northeast coast of Florida:

1. Brackish water desalination using ED or RO may prove to be a viable alternative
for this coastal region.

2. Seawater desalination using RO can be cost-effective for larger municipal water
supplies (>5 mgd).

3. Co-location with power generation facilities should be considered for dilution of
concentrate from the desalination process. The possibility for negotiated-lower
energy rates should also be investigated.

4. Continue to monitor the development of emerging technologies for advancements
related to evaporation technologies for producing a dry salt from the RO
concentrate.

5. Continue to monitor the development of pretreatment system improvements,
particularly microfiltration, and other processes for their ability to handle
fluctuating raw water qualities with high turbidities.

6. Consider new, proven technologies that have been demonstrated at a commercial
scale. Some new technologies, which claim less energy or greater product water
recovery, must be proven in a full-scale, operational facility, where treatment
effectiveness, energy efficiency and costs can be proven. Some emerging
technologies currently in development may prove to be great advancements in the
desalination field; others may not.


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Demineralization Technologies Technical Memorandum



9.0 REFERENCES


1. Aquasonics web site (http://www.aquasonics.com)
2. Buros, O.K., "The Desalting ABC's". International Desalination Association,
second edition, February 2000.
3. Conlon,W.J. and Jhawar, M., "Pretreatment of Membrane Processes with
Ultraviolet Disinfection," paper for American Water Works Annual Conference
and Exposition, San Antonio, Texas, June 1993.
4. Conlon W.J. and Rohe, D., "Energy Recovery in Low Pressure Membrane
Plants", Proceedings of the First Biennial Conference, Is Current Technology the
Answer? National Water Supply Improvement Association, Washington, D.C.,
June 1986.
5. DesalNATE website (http://www.worldwidewaters.com/sys.html)
6. Koch Fluid Systems web site (www.kochmembrane.com)
7. New Technique Developed by Tech Researchers for Economical Desalinization
of Produced Water, New Mexico Tech Research & Economic Development
Office, http://www.nmt.edu/-red/horizon/2001/desalin.html.
8. Truby, R., "Desalination Processes Enhanced by Multiple Membrane Systems",
European Conference on Desalination and the Environment: Water Shortage,
Lemesos, Cyprus, May 28-31, 2001.
9. Vari-RO systems web site (http://www.usbr.gov/water/media/pdfs/report033.pdf)


Seawater Demmeralhzation Feasibility Investigation Demmeralization Technologies Technical Memorandum




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