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 Cover
 Executive summary
 Acknowledgement
 Table of Contents
 List of Figures
 List of Tables
 List of appendices
 List of abbreviations and...
 Introduction
 Water for the future
 Desalination: The technology and...
 Desalination concentrate manag...
 Conclusions
 References
 Appendices


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Desalination in Florida: Technology, Implementation, and Environmental Issues
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Title: Desalination in Florida: Technology, Implementation, and Environmental Issues
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Creator: Drew, Richard
Publisher: Florida Department of Environmental Protection
Place of Publication: Tallahassee, Fla.
Publication Date: April 2010
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Table of Contents
    Cover
        Cover 1
        Cover 2
    Executive summary
        Page i
        Page ii
    Acknowledgement
        Page iii
    Table of Contents
        Page iv
        Page v
    List of Figures
        Page vi
        Page vii
        Page viii
    List of Tables
        Page ix
    List of appendices
        Page x
    List of abbreviations and acronyms
        Page xi
        Page xii
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
    Water for the future
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
    Desalination: The technology and application in Florida
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
    Desalination concentrate management
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
    Conclusions
        Page 59
        Page 60
    References
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
    Appendices
        Page 76
        Page 77
        Page 78
        Page 79
        Page 80
        Page 81
        Page 82
        Page 83
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Full Text








Desalination in Florida:


Technology, Implementation, and

Environmental Issues



Division of Water Resource Management
Florida Department of Environmental Protection
April, 2010


3900 Commonwealth Boulevard, MS 41
Tallahassee, Florida 32399-3000
www.dep.state.fl.us iFLOA


M










Desalination in Florida: A Brief Review of the Technology,
Environmental Issues and its Implementation.

This report was prepared in response to the interest in the development of
alternative water supplies and specifically desalination in Florida. It is an
assessment of current technologies and its application in the state.
Recommendations are provided to effectively implement environmentally
and fiscally sound desalination technologies that will hopefully help meet
current and long-term potable water supply demands of the state's
growing population.




April 21, 2010






















3900 Commonwealth Boulevard, MS 41
Tallahassee, Florida 32399-3000
www.dep.state.fl.us FO A








EXECUTIVE SUMMARY


Florida cannot meet its future demand for water by relying solely on the development of
traditional ground and surface water sources. The state's water demand is expected to grow
by greater than 25% to about 8.7 billion gallons per day by the year 2025. To meet this
demand, we must continue to diversify our sources of water to include environmentally sound
use of saltwater, brackish surface and ground waters, the collection of wet-weather river flows,
and reuse of reclaimed water and stormwater. Water conservation, though not typically
thought of as an alternative water supply, is also critical to our water supply strategy as a cost
effective means of achieving efficient utilization of water and ensuring the sustainability of the
diverse water resources of the state. Desalination, or the removal of salts from seawater and
brackish water sources, is one of several alternative water supplies identified by Florida's
water managers as needed to meet the projected increase in demand. The "drought resistant"
nature of desalination makes it an attractive alternative to those water sources that rely on
rainfall.

Florida leads the nation in the use of desalination technology, in both the number of facilities
using the process (more than 140) and the gallons of potable water produced each day (about
515 million gallons). This is reflective of efforts to meet the needs of the state's increasing
population while avoiding overuse of traditional drinking water sources, particularly in
coastal areas of central and south Florida. The majority of the source water treated at
desalination plants in Florida is not saltwater, but brackish ground and surface waters. Today,
only a few Florida plants draw their source water from coastal seawater. The Tampa Bay
Seawater Desalination Facility is the only large-scale reverse osmosis facility in the state using
a coastal surface water source. However, seawater desalination technology is being
considered for application to other areas such as the Coquina Coast project in Flagler County
in Northeast Florida where land-based and novel ship-based approaches are being considered.

Desalination can be accomplished by distillation, electrodialysis, and reverse osmosis
technologies. In Florida, as in much of the United States, reverse osmosis (RO) is by far the
dominant technology used. This is primarily due to the higher energy costs of the other








technologies. The prevalence of RO, as a stand-alone technology, may evolve to combination
systems, where membrane technology (like RO) is linked to a distillation process, lowering
energy requirements of either stand-alone technology. Modifications of the traditional RO
process, including more energy efficient pumps, longer lasting membranes, and blending of
existing technologies like distillation are reducing the costs of desalination. The increasing
costs of traditional water supply and the reduction in costs of RO technology result in
desalination becoming more cost competitive.

The type of source water (surface or ground, salt or brackish), the desalination technology
employed, and the concentrate management method used are significant factors affecting the
environmental evaluation and regulation of these facilities. In addition, desalination
technologies have greater energy consumption and associated greenhouse emissions
compared to other traditional water supplies. As the salt content of the source water increases
from brackish water to seawater, there is a proportional increase in the energy usage and
greenhouse gas emissions. The use of alternative energy sources like waste heat or solar can
reduce the need for fossil fuel based energy. Co-location of desalination facilities at or near
existing power plants or large municipal wastewater treatment plants can minimize
environmental impacts through the use of existing intake and outfall structures and the
blending of desalination brine and power plant heated effluents. In addition, co-location can
reduce energy needs (heated source water improves the efficiency of the desalination
membranes), reduce capital cost (use of existing intake and outfall structures, reduced power
line connection costs, and reduced property and zoning costs from the use of an existing
industrial site footprint) and reduce operational costs (heated source water reduces
degradation of membranes and efficiency of salt removal).

Given the large number of desalination plants in Florida, and the anticipated development of
new facilities over the next 10 years, desalination has already been determined to be a feasible
and cost- effective supply alternative by water supply utilities. Technological improvements
and continued cost-sharing of alternative water supply development by the water
management districts and the State could hasten the wider application of desalination
technology.








Acknowledgements


Many individuals assisted in the development of this report, either through contributions,
reviews, or both. David Trimble, Ken Carter, Dan Peterson, Bonnie Hall, Al Hubbard, Jeffrey
Lawson, and Kevin Ledbetter of the Department of Environmental Protection contributed
significantly to the writing of several sections of the report and researching the current and
growing field of desalination. The St. Johns River, Southwest Florida, and South Florida Water
Management Districts and specifically Barbara Vergara, Ken Herd, and Ashie Akpoji, Mark
Elsner, and Marjorie Craig all provided critical review and valuable suggestions. Each of these
water management districts is a valuable resource on the subject of desalination in Florida,
providing a wealth of information.

In addition to Florida-specific information provided by the water management districts, the
development of this report was greatly aided by the recent and comprehensive examination of
desalination in the United States, crafted by the National Research Council, of the National
Academies, "Desalination, A National Perspective". Anyone wanting to understand the
subject and the rapidly growing field of knowledge is encouraged to read this report.

Finally, as editor of this report, I take full responsibility for errors and mistakes, and place full
credit on what is good on those listed above.

Richard Drew, Chief, Bureau of Water Facilities Regulation, Division of Water Resource
Management, Florida Department of Environmental Protection








CONTENTS


Executive Summary........................................................................................ i

Acknowledgements.................................................... .............. ....... ............. iii

Table of Contents.................................................... .............. .......................... iv

List of Figures .......... ......................... ........... ......... ........................vi

List of Tables ......... .......................... ........... ............. ...............................ix

List of Appendices..................................................... ............... ....... ............. x

List of Abbreviations and Acronyms.................................................... ................xi

SECTION ONE: Introduction.................................................... ...................1

SECTION TWO: Water for the Future............................................................7

IViatcr Use Trends .......................................... .... ...... .. ......................... 7

I 1atcr Protection and Sustainability Program.......................................................... 11

Desalination for Future 1'V1tcr Supply..................................................................... 13

SECTION THREE: Desalination: The Technology and Application in Florida............ 15

3.1 A Brief H history ..................................................... ................ ................. 15

3.2 Desalination Process.................................................... ........................... 15

Reverse Osmosis ................ ............ ......... ................... ...... .............. 18

Electrodialysis Reversal........................................................................... 19

Distillation................................................................. 19

3.3 Recent Technology................................................................................. .. 22

3.4 Key Components of Desalination Process .................................................... 25

Intake Structures and Conveyance.................................................................. 26

Pretreatment ............................... .............................. .................. ..... 27

Reverse Osmosis Treatment.................................................................. .... 27

Post-Treatm ent................................... ...................... ... ... ... ..................... 28




3900 Commonwealth Boulevard, MS 41
Tallahassee, Florida 32399-3000
www.dep.state.fl.us FLOR A








CONTENTS (Continued)


Concentrate Management............................................................................ 29
Offshore Desalination.................................................... ............................29
3.5 Cost...........................................................................31

Cost Estimates of Co-Located Desalination Facilities.............................................34
3.6 Florida's Membrane Plants....................................................................... 35

SECTION FOUR: Desalination Concentrate Management.......... ............................ 40
4.1 The Regulations......................................... ....................................... 40
4.2 Source, Technology, and Management Options................................. .......... 41

4.3 Desalination Concentrate Discharge and Management Options............... ........ 44

Discharge to Domestic IVaistcliater Treatment Collection Systems.............................45

Direct Surface 1'aVter Discharge..................................................................... 46
Land Application and Blending with Reclaimed IViater for
Recharge and Irrigation............................................................................... 48
Deep Well Injection...................................................................... .........49

Concentrate Blending at Co-Located Coastal Electric Power Plants........................... 51
4.4 Potential Environmental Issues for Surface Water Discharges.......................... 53
C circulation ...................................................... ...................................... 55

Dissolved Oxygen........................................... ..................................... 56
Other Parameters ............................................. ......................................... .. 56

SECTION FIVE: Conclusions ................................................ .................. 59

REFERENCES.............................................................................................. ... 61


APPENDICES ............................................................................................. 76






3900 Commonwealth Boulevard, MS 41
Tallahassee, Florida 32399-3000
www.dep.state.fl.us FLOR A








CONTENTS (Continued)


List of Figures

Figure 1-1. Lake Region Water Treatment Plant, Belle Glade, Florida.............................1

Figure 1-2. Total Desalination Capacity by Country.................................................4

Figure 1-3. States with the Highest Desalination Production...................................... 5

Figure 1-4. Desalination Facilities in Florida..................................... ............... 6

Figure 2-1. Florida's W ater Management Districts...................................................7..

Figure 2-2. Statewide Freshwater Withdrawals and Population Growth.........................8

Figure 2-3. Total Freshwater Use by Water Management District.................................. 8

Figure 2-4. Statewide Freshwater Demand Projections and Water Use Categories ...........9

Figure 2-5. Historic Public Water Supply Withdrawals and Population Served ...............10

Figure 2-6. Statewide Total Freshwater Use .......... ........................................ ........ 10

Figure 2-7. Statewide Summary of Types of Alternative Water Supply Projects Funded..... 12

Figure 2-8. Quantity of Water Created by Alternative Water Supply Projects................. 12

Figure 3-1. The Structure of the Diatom Algae Being Reproduced Using Nanotechnology to
Create More Efficient Membranes for Desalination .............................................15

Figure 3-2. A Summary of Water Desalination Processes.......................................... 18

Figure 3-3. Flow Diagram of the Tampa Bay Water Seawater Desalination
F facility ....................................................................................... 25




3900 Commonwealth Boulevard, MS 41 r
Tallahassee, Florida 32399-3000
www.dep.state.fl.us FLOR A








CONTENTS (Continued)


Figure 3-4. Tampa Bay W ater Desalination Plant.......................................................26

Figure 3-5. Tampa Bay Water Desalination Facility Reverse Osmosis Membranes ............28

Figure 3-6. Post Treatment Lime Softening Using Slaked Lime..................................... 28

Figure 3-7. A Summary of Desalination Concentrate Management Methods in the United
States .......................................................................... .............. 29

Figure 3-8. Shipboard Desalination..................................................... ................. 30

Figure 3-9. Reverse Osmosis Production Cost Curves Using Brackish Groundwater
as a Source W ater .................... ....................................... ..............................33

Figure 3-10. Reverse Osmosis Production Cost Curves Using Brackish Surface
W ater as a Source W ater................................................................................ .. 33

Figure 3-11. Reverse Osmosis Production Cost Curves Using Seawater
as a Source W ater .................... ...................................... ..............................34

Figure 3-12. 2009 Potable Water Desalination Plants in the South Florida Water Management
D istrict................................................................... ........ ............................. 37

Figure 3-13. Growth of Desalination Potable Water Production in the South Florida Water

M anagem ent District .. ............ ...................................................................... 38

Figure 3-14. Growth of Desalination in the South Florida Water Management District....... 39

Figure 4-1. Seawater Desalination Plant with Marine Discharge, Perth, Australia..............40







3900 Commonwealth Boulevard, MS 41 r
Tallahassee, Florida 32399-3000
www.dep.state.fl.us FLOR A








CONTENTS (Continued)


Figure 4-2. Side View of a Fish Exclusion Screen around a Surface Water Intake
Structure........................................................................................................... 43

Figure 4-3. Directional Drilling to Install Intake Piping Below the Seabed.................... 43

Figure 4-4. Desalination Concentrate Management Methods in Florida.......................... 45

Figure 4-5. Example of a Effluent Diffuser System..................................................48

Figure 4-6. An Idealized Cross-section of an Underground Injection Control Well..........49

Figure 4-7. Process Overview for Co-Location of a Desalination Plant and Steam
Electric Pow er Plant....................................... .............. ................................. 51

Figure 4-8. Aerial View of a Desalination Plant Co-Located with a Steam Electric
Pow er Plant............ ..... ...... ...... .. ......................................................... ............ .. 52

Figure 4-9. Illustration of the City of Hollywood Water Treatment Plant Using a Combination
of Reverse Osmosis and Nanofiltration to Treat Source Waters from Two
A quifers...................................................... ......................................... 53



















3900 Commonwealth Boulevard, MS 41 r
Tallahassee, Florida 32399-3000
www.dep.state.fl.us FLOR A








CONTENTS (Continued)


List of Tables

Table 2-1. Funding Distributions for Alternative Water Supply through the Water Protection
and Sustainability Program ......................................... ............................... 11

Table 3-1. Filtration Treatment Processes and the Pollutants Removed........................ 17

Table 3-2. Comparison of Predominant Seawater Desalination Processes........................20

Table 3-3. Comparison of Predominant Brackish Water Desalination Processes................21

Table 3-4. Recent Desalination Innovations...................................... .......................24

Table 3-5. Summary of Estimated Costs to Build and Operate Reverse Osmosis Desalination
Facilities at Port Everglades, Lauderdale, and Fort Myers Power Plant Sites.................35

Table 3-6. Characterization of Desalination Plants in Florida...................................... 36

Table 4-1. Reported Dosing Concentrations of Pretreatment Chemical Additives in Reverse
O sm osis Desalination..................................................................... ..........57

Table 4-2. Typical Nanofiltration and Reverse Osmosis Cleaning Formulations ..............58


















3900 Commonwealth Boulevard, MS 41 r
Tallahassee, Florida 32399-3000
www.dep.state.fl.us FLOR A








CONTENTS (Continued)


List of Appendices

Appendix A: Reverse Osmosis (RO) Membrane Technologies.................................... 76

Appendix B: Thermal Distillation Processes....................................................... .. 81

Appendix C Recent Desalination Technology Innovations..................................... 87

Appendix D Desalination Pretreatment Considerations...........................................96

Appendix E Concentrate Management Challenges and Limits..................................100

Appendix F FDEP Regulated RO Facilities........................................................ 101

Appendix G Desalination Links.................................................... .................... 105


3900 Commonwealth Boulevard, MS 41
Tallahassee, Florida 32399-3000
www.dep.state.fl.us


FLROR ,








CONTENTS (Continued)


List of Abbreviations and Acronyms

ASR: aquifer storage and recovery system
BGD: billion gallons per day
C: degrees Celsius
CAB: cellulose acetate
CPA: composite polyamide
CWA: Clean Water Act
EDR: electrodialysis reversal
FDEP: Florida Department of Environmental Protection
kgal: one thousand gallons
kgal/d: thousand gallons per day

kJ/kg: kilojoules per kilogram
kWh: kilowatt-hour
m3: cubic meters

MGD: million gallons per day
MED: multiple effect distillation
mg/L: milligrams per liter
MSF: multistage flash distillation
MVC: mechanical vapor compression
NaOH: sodium hydroxide
NF: nanofiltration
NPDES: National Pollutant Discharge Elimination System
O&M: operation and maintenance

ppt: parts per thousand (g/L)
ppm: parts per million
psi: pounds per square inch



3900 Commonwealth Boulevard, MS 41
Tallahassee, Florida 32399-3000
www.dep.state.fl.us FLOR A








CONTENTS (Continued)


PWS:
RO:

SDV:

SFWMD:

SJRWMD:
SRWMD:
SWFWMD:

TDS:

TFC:
TVC:
UIC:
USDW:

USEPA:

VC:
VVC:
WWTP:


public water systems
reverse osmosis

Seawater Desalination Vessel

South Florida Water Management District

St. Johns River Water Management District
Suwannee River Water Management District

Southwest Florida Water Management District
total dissolved solid

thin film composite

thermal vapor compression

Underground Injection Control
Underground Source of Drinking Water

United States Environmental Protection Agency
vapor compression

vacuum vapor compression
wastewater treatment plant


3900 Commonwealth Boulevard, MS 41
Tallahassee, Florida 32399-3000
www.dep.state.fl.us


IRORIA






Florida Department of Environmental Protection, Desalination in Florida


SECTION ONE: Introduction


During the 2008 Florida Legislative
session, House Bill 199 recognized the
treatment of saltwater to produce potable
water, or desalination, to be a proven
technology advanced around the world.
The bill directed the Department of
Environmental Protection to work with
the Water Management Districts to

examine this technology's usefulness to
Figure 1-1. Lake Region Water Treatment Plant, Belle examine this technology's usefulness to
Glade, Florida (SFWMD, 2009) Florida. While the bill did not pass, the

Department agreed to undertake the tasks outlined in the proposed legislation. To that end
this report will:

Examine current and available desalination technologies,
Provide an analysis of existing desalination projects in the state, and
Provide recommendations to effectively implement desalination in an environmentally
safe and cost effective manner.

Until the last few decades, Floridians have enjoyed what appeared to be a limitless supply of
freshwater, mostly contained in readily-accessible shallow aquifers under most of the land
surface area of the state. This was evidenced by the presence of springs from Miami to the
Panhandle. As the population grew, its water use grew. Just as the presence of springs
exemplified the abundance of water in the early part of the twentieth century, the
disappearance of springs along the southeastern and southwestern coasts provided the early
warning signs of diminishing groundwater supplies (Ferguson, et al., 1947).

Today, we face saltwater intrusion along the coastlines, as well as intrusion of more salty deep
aquifer waters into shallower freshwater aquifers (Causseaux and Fretwell, 1983; Koszalka,

1994; Tihansky, 2005). Growth, particularly along the central and southern Florida coasts, has
caused some drinking water utilities to change treatment to deal with a decline in existing


April 2010 Page 1 of 109






Florida Department of Environmental Protection, Desalination in Florida

water sources and treat poorer quality source waters to meet increasing water needs (Merejo,
et al., 2005; Elarde, et al., 2005).

In a number of locations around the state, dwindling groundwater supplies have resulted in
the designation of areas of critical water supply, water use caution areas, water resource
caution areas, and priority water resource caution areas by the state's water management
districts. These designations typically result in greater limitations on water use and more
stringent conditions for obtaining, renewing, or increasing the allocation authorized by

consumptive use permits. For example, in the Central Florida region the water management
districts, through water supply planning and individual permit actions, have determined that
growth in public water supply over the next 20 years from traditional groundwater sources is
not sustainable. In some instances, groundwater withdrawals have already resulted in
impacts to wetlands and spring flows. As a result, the South Florida, Southwest Florida, and

St. Johns River water management districts are working together to determine the limit of
available groundwater supplies in the area and identify alternative sources of water to meet
Central Florida's water demands. The districts are also working together to develop long-term
rules for the area by 2013 (SJRWMD, 2009). These efforts are described in Section 2 of this
report.

Clearly, Florida cannot meet its future demand for water solely through traditional ground
and surface water sources. Florida must continue to diversify its water supply sources to
include a range of environmentally sound alternative supplies including saltwater, brackish
surface and ground waters, surface water collected primarily from wet-weather flows, reuse of
reclaimed water and stormwater, and conservation (AWWA, 2008; Henthorne, 2008; Heimlich,

et al., 2009). Section 2 of this report will provide a more detailed look at the present and future
water needs of the state and the specific efforts to develop desalination.

While most of the state has had, until recently, an adequate water supply, there were areas,
such as the Florida Keys and some barrier islands, where freshwater was never plentiful. It

wasn't unusual, in the early 1900's, to find cisterns to collect rainwater in coastal and barrier
island homes. A shallow lens of freshwater in the surficial aquifer system floated on top of the
saltwater in the barrier islands, providing an additional but very limited supply of freshwater.


April 2010 Page 2 of 109






Florida Department of Environmental Protection, Desalination in Florida


It was in these areas of limited freshwater that the first attempts were made to extract
freshwater from saltwater (desalting or desalination) using distillation (the process of heating

water to a boil and condensing the water vapor through cooling tubes).

Distillation is an old technology used on the open seas. Sir Richard Hawkins reported in 1662
that, during his voyages to the South Seas, he was able to supply his men with freshwater by
means of shipboard distillation (Birkett, 2003). Thomas Jefferson, as Secretary of State,
encouraged research on the concept of desalination in the 1790s and was responsible for
having desalination methods printed on the back of every permit issued for vessels sailing
from U.S. ports (Wilson, 2001).

Distillation was used to produce the first land-based water supply facilities in the 1920s and
1930s in the Caribbean and Mideast. In the U.S. at the 1961 dedication of a vertical distillation
plant in Texas, President Kennedy, made an insightful statement on the importance of
desalination then and for the future, "No water resources program is of greater long-range
importance than our efforts to convert water from the world's greatest and cheapest natural resources -
our oceans into water fit for our homes and industry. Such a break-through would end bitter
struggles between neighbors, states, and nations."

As with the Texas facility, various forms of distillation were the mainstay of the desalination
industry, until a few decades ago, when innovations in reverse osmosis (RO) technology
lowered its costs. Since then, RO use has expanded exponentially. Today, distillation
technologies still generate 43% of the world's desalinated waters (NRC, 2008). However, in
the United States, distillation or 'thermal' technology represents only 3% of the water
production, whereas RO, a membrane filtration technique, produces 96% of the nation's
desalinated water.

Reverse osmosis is a process that uses pressure on a salty source water to push the water
molecules through a membrane. The salts remain behind the membrane in a saltier
concentrate for later disposal. More than 12,000 desalination plants operate around the world
today and have the capacity of producing 11 billion gallons of water each day (See Figure 1-2).
In 2005, the U.S. contained more than 1,100 facilities with the capacity of about 1.5 billion


April 2010 Page 3 of 109






Florida Department of Environmental Protection, Desalination in Florida


gallons per day. Today, almost 100% of the municipal desalination facilities in the country use

reverse osmosis and other similar membrane treatment technologies.





W - -. ,' --. - . -. -.-.- -00o 00
1"0 loW IMa 8 sW Mw 1)" 01 ME "M*E I[E IV-


Li ned Srle ".. ..
1493.6o0 0 8m I L
/' h I


Is n -unlge S I 3 as iu a
i F U rt tes lr 44 I
s ,--Sau udi b --_La
tcn 1g1t country. Te p t o p b d n we hr is m tha w
S ----- Kwai B '}
hat g i 567.81--. ; s


< 'L ', ; i ' .' '
S... Scale
S- 1:175,000,000
iai* moVw IHew Mw 3aY o0 Mo' UE I*E I[WE la
Total Online Capacity (MGD): 0.000264 to 1.32 n 1.32 to 13.21 N 13.21 to 13209 N 132.09 to 264.17 Above 264.17

Figure 1-2. Total Desalination Capacity by Country (Adapted from GWI, 2006)

These and other desalination technologies are described in more detail in Section 3 of this

report.


In addition to a brief description of existing and new technologies, Section 3 also includes a

discussion of the Florida-specific facilities. Florida has set the pace in the use of desalination

technology in this country. The production of potable drinking water here is more than twice

that generated in the second highest production state, California (Figure 1-3; NRC, 2008). This

is reflective of the state's increasing population, especially along the central and southern

coastal regions of the state and the finite availability of freshwater, as illustrated by the

location of the desalination facilities shown in Figure 1-4. As the well fields serving these areas

moved inland, the economics of transporting freshwater ever increasing distances to the point

of use made membrane filtration of lower quality nearby water more cost effective. For the

most part, the source water treated at desalination plants in Florida is not saltwater as the

name would suggest, but mainly less salty brackish ground and surface waters (full strength


April 2010 Page 4 of 109






Florida Department of Environmental Protection, Desalination in Florida

seawater contains about 35,000 mg/1 of total dissolved solids [TDS] various salts, chiefly

sodium and chloride; brackish water will typically range from 1,000 to 20,000 mg/1 TDS).

Today, only a few sites draw their source water from coastal seawater. However, one of those,

the Tampa Bay Water desalination facility, is the largest reverse osmosis facility east of the

Mississippi River. Future development and application of seawater desalination technology is

being studied for application to other areas in the state. The Coquina Coast desalination

project in Flagler County, northeast Florida, is one example of a potential regional system

being explored, and is described in more detail in Section 3 and at the St. Johns Water

Management District (SJRWMD) web site, http://sjr.state.fl.us/coquinacoast/index.html.

As mentioned earlier, the by-product of desalination is a brine or concentrate that must be

safely managed. Management options depend on the source water chemicals that will be

concentrated, the degree of concentration, and the disposal alternatives (surface waters,

underground injection, and land application) available to the facility's specific location.

Section 4 provides a discussion of the environmental considerations tied to concentrate

management.



660


528----

| Other
S3 ] Power
SIndustrial (captive)
U 2,:4-- I Mllunicipal

o
-4--





Florida California Texas Arizona Virginia Colorado Alabama Hawaii Oklahoma
Figure 1-3. States with the Highest Desalination Production (Adapted from GWI, 2006)


April 2010 Page 5 of 109







Florida Department of Environmental Protection, Desalination in Florida


-F



!I~


t~ ii


ctl .


\


N Ni
,I\ ^..t

.


+q1


--~s)


0b -

II~*


LT
ix
-'4.. .
o "K


0 1020 49. 60 80
-- -- Mldes


Figure 1-4. Desalination Facilities in Florida (FDEP, 2009)


April 2010 Page 6 of 109


6o
eo
o


Desalination:
Reverse Osmosis Plants

Produced Water
Design Capacity (gpd)

o 0-2,250,000
2,250,001 6,600,000
6,600,001 18,100,000
* 18,100,001 37,500,000
* 37,500,001 70,lOilO,00


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Florida Department of Environmental Protection, Desalination in Florida


SECTION TWO: Waterfor the Future


Clean and plentiful water is critical to Florida's economy and quality of life. Florida is a water
rich state, with over fifty inches of rainfall per year, and some of the most prolific aquifers in
the nation. However, Florida's
growing population and cyclical

patterns of drought and flood
make meeting the needs of all
existing and future water users,
while also protecting the state's Figure 2-1. Florida's Water
diverse natural resources, a Management Districts
challenge. Florida's five water
management districts (Figure 2-1)
are charged with identifying
adequate sources of water to meet
Florida's 20-year demands.

Chapter 373, Florida Statutes, requires the districts to develop regional water supply plans for
any area where existing sources are deemed inadequate to meet projected 20-year demands
without harm to the environment or existing legal users of water. Four of the five districts
have identified such areas and have developed regional water supply plans that identify
sources to meet foreseeable demands through the year 2025. These include alternative sources
such as surface water, brackish groundwater, reclaimed wastewater, stormwater, or
desalinated seawater, and increased water use efficiency.

This section of the report provides information on statewide water use trends and projections,
planning efforts to meet future water use needs, and the role that desalination is expected to
play in the state's water supply strategy.

Water Use Trends

Floridians used an estimated 6.8 billion gallons per day (BGD) of freshwater in 2005. The most

recent projections performed by the water management districts (2007-2008) forecast water


April 2010 Page 7 of 109







Florida Department of Environmental Protection, Desalination in Florida

demands of about 8.7 BGD in 2025 (Figure 2-2). Projections out to 2030 are currently being

developed.


10 I Water Use -*-Population 25
To understand trends in water '

withdrawals, it is important to 8 20

look both within water use 3 6 15,
15
sectors and within regions of the
4 10
state. Figure 2-3 shows the 1

distribution of freshwater 2 5

withdrawn in each water 0 -

management district since 1975. 2000 2005 2010 2015 2020 2025

In the northern part of the state, Figure 2-2. Statewide Freshwater Withdrawals and Populati
Growth (FDEP, 2008a)
total freshwater withdrawn

since 1975 has remained relatively stable. Water withdrawals in the South Florida Water

Management District (SFWMD) show an increasing trend, and represent about 50 percent of

all withdrawals in the state.


4




3


-4-SFWMD
"- --SWFWMD
S-SJRWMD
S--NWFWMD
-)SRWMD
1




0
1975 1980 1985 1990 1995 2000 2005

Figure 2-3. Total Freshwater Use by Water Management District (FDEP, 2008a)

Use also varies by sector. Agriculture currently is the largest user of freshwater in the state;

however, public water supply is projected to become the largest user by 2010 (Figure 2-4).


10



0
-4


on


April 2010 Page 8 of 109






Florida Department of Environmental Protection, Desalination in Florida


10
o Power Generation

M8 Commercial/ Industrial/
SInstitutional
6 0 Recreational Irrigation

0] Agricultural Irrigation
p 4
SI I Domestic and Small
2 Public Supply
1 Public Water Supply


2000 2005 2010 2015 2020 2025


Figure 2-4. Statewide Freshwater Demand Projections and Water Use Categories (FDEP, 2008a)

Based upon water management district projections, public water supply will account for the

majority of overall growth in statewide demand between 2005 and 2025. The regional water

supply plans estimate that, by 2025, demands in public water supply will increase by about

49% and account for about 43% of the total estimated use of 8.7 BGD. Agriculture will be the

second largest use, but will only increase by about 6%.

Figure 2-5 shows the amount of water historically used for public water supply and the

population served. It shows a large overall increase in water withdrawn since 1950, and also

that water use has been increasing in direct proportion to population growth. This trend could

be altered by more emphasis on water conservation and by greater use of reclaimed water.


April 2010 Page 9 of 109






Florida Department of Environmental Protection, Desalination in Florida


3.0 18







1 .0-10


a c i -- in ... A s 1 F

0.0 i 0 0
-4 J



1950 1955 190 1965 1970 1975 1980 1985 1990 1995 2000 2005

Figure 2-5. Historic Public Water Supply Withdrawals and Population Served (FDEP, 2008a)

Water use and demographic trends in Florida suggest that source diversification is an

important consideration in meeting future needs. As shown in Figure 2-6, since 1975, Florida

has relied more heavily on fresh groundwater than surface water to meet water supply needs.

In 2005, groundwater 6

withdrawals accounted for

about 62% of all freshwater .

withdrawals in the state. More U 4

significantly, about 90% of water q

withdrawals for public supply,

the use sector which will u 2
S-*-Groundwater
account for most of the -*-Surface Water

anticipated growth in water use,

have historically come from 0 -
1975 1980 1985 1990 1995 2000 2005
groundwater. Supplies of fresh,
inexpensively treated Figure 2-6. Statewide Total Freshwater Use (USGS, 2008)

groundwater are increasingly limited in many parts of the state, prompting water planners

and suppliers to put increasing focus on the development of alternative water supplies to use

in conjunction with existing groundwater sources. A mix of water supply sources, that can be


April 2010 Page 10 of 109






Florida Department of Environmental Protection, Desalination in Florida

combined or rotated depending on conditions and needs, offers many benefits. A diversified

supply source affords a better ability to protect natural resources, deal with drought and flood
periods (and potential effects of climate change), and provide more reliable water delivery to

users. Desalination is expected to play an important role in Florida's diversified water supply

portfolio.

Water Protection and Sustainability Program

In 2005, the Florida Legislature created the Water Protection and Sustainability Program to

encourage the development of alternative water supplies as a way to meet future needs. This

program provides state funds to the water management districts for alternative water supply

project construction as shown in Table 2-1. These funds, along with matching district funds,

are awarded as grants to local water suppliers.

Water Management FY 2005 2006 FY 2006 2007 FY 2007- 2008 FY 2008 2009
District ($ millions) ($ millions) ($ millions) ($ millions)
South Florida 30 18 15.6 4.25
Southwest Florida 25 15 13 0.75

St. Johns River 25 15 13 0

Suwannee River 10 6 5.2 0.27

Northwest Florida 10 6 5.2 0.27

Total 100 60 52 5.54


Table 2-1. Funding Distributions for Alternative Water Supply through the Water Protection and
Sustainability Program (FDEP, 2010)

Between 2005 and 2008, the water management districts provided funding assistance to local

water suppliers for the construction of 327 projects. Figure 2-7 shows that approximately 63%

of the projects funded were reclaimed water projects. The next most common group of

projects funded were brackish groundwater desalination projects, which comprised

approximately 22% of the total.


April 2010 Page 11 of 109







Florida Department of Environmental Protection, Desalination in Florida

The districts estimate that when construction of these projects is complete they will help create

approximately 761 MGD of "new water," which is about 38% of the 2 BGD of water needed by

2025. Figure 2-8 shows that reclaimed water projects are expected to produce the largest

amount of water, approximately 267 MGD, which is about 13% of the additional water needed

by 2025.




250 1


O NWFWMD
O SRWMD
O SJRWMD
O SWFWMD
O SFWMD


18 16
I | I I 9 ,


SJRWMD

5 1


Reclaimed Brackish
Water Groundwater


ASR Surface Water


Other Stormwater Seawater


Figure 2-7. Statewide Summary of Types of Alternative Water Supply Projects Funded
(FDEP, 2010)1


800

700

600

500

400

300

200

100

0


7609


O Quantity of Water Created when Projects Completed

O Quantity of Water Already Created


IF- I-I


F-I----


Total Reclaimed Brackish GW Surface Other Seawater ASR Stormw
Water

Figure 2-8. Quantity of Water Created by Alternative Water Supply Projects (FDEP, 2010)


1 ASR: aquifer storage and recovery system


April 2010 Page 12 of 109


205


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. 100-
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Florida Department of Environmental Protection, Desalination in Florida


Brackish groundwater desalination projects are expected to produce the next largest amount of
water, approximately 223 MGD, or about 11% of the additional water needed by 2025. The
program has provided funding for only one new seawater desalination project to date, the
Coquina Coast project in Flagler County. Funding for the Water Protection and Sustainability
Program was discontinued in fiscal year 2009-2910, eliminating state-level participation in the
funding of alternative water supply projects.

Desalination for Future Water Supply

Florida has significant future needs for additional water, a portion of which will be met
through desalination. The water management districts have been active in evaluating
opportunities for both seawater and brackish water desalination. The Southwest Florida
Water Management District (SWFWMD) assisted in the development of the seawater
desalination facility operated by Tampa Bay Water. Three other seawater sites in that region
have been studied, which together with the existing Tampa Bay Water desalination facility,
have the potential to bring the total production from seawater desalination to 75 MGD. The
district's Regional Water Supply Plan also identifies a considerable number of existing and
proposed brackish water desalination projects within the 10-county planning region, primarily
in Charlotte, Pinellas and Sarasota Counties.

The St. Johns River Water Management District (SJRWMD) is assisting a consortium of utilities
in planning the development of the Coquina Coast seawater facility in Flagler County

(http:/ /www.sjrwmd.com / coquinacoast/index.html). The partners include Volusia, Flagler,
Marion and St. Johns counties, the Dunes Community Development District, and the cities of
Palm Coast, Deland, Mount Dora, Leesburg, Bunnell, and Flagler Beach. Eleven other
potential sites were identified, three of which remain under consideration, though none have
been selected for implementation at this time. As with the Southwest and South Florida
districts, brackish water desalination is a significant component of water supply within the St.
Johns River district.


April 2010 Page 13 of 109






Florida Department of Environmental Protection, Desalination in Florida

In the South Florida district, investments by utilities in desalination, assisted by grants from

the district, have resulted in doubling the amount of desalinated water and number of plants

in the last 10 years. Currently, there are 29 brackish water and two seawater plants in

operation. Eight brackish water plants are under construction and are expected to be

completed before 2012. Total capacity is expected to reach 250 MGD by 2012 (SFWMD, 2009).


April 2010 Page 14 of 109






Florida Department of Environmental Protection, Desalination in Florida

SECTION THREE: Desalination The Technology and Application in Florida


3.1 A Brief History

As mentioned previously,
Sthe history of desalination
in the United States can be
traced back to the 1790's

when Secretary of State

Thomas Jefferson evaluated
.a proposal to provide

Figure 3-1. The Structure of the Diatom Algae Being Reproduced affordable, freshwater to a
Using Nanotechnology to Create More Efficient Membranes for fledgling US Navy. In
Desalination (Copyright CSIRO Australia, 2009)
Florida, the commercial use

of modern desalination plants dates back to the latter part of the nineteenth century. Today
Florida leads the nation in desalination, accounting for about 40 percent of the country's
freshwater produced from seawater and brackish ground and surface waters. In the South
Florida Water Management District (SFWMD) boundaries alone, there are 29 brackish and two

seawater desalination plants In that region, eight brackish water plants are under construction
and collectively will produce 250 MGD of potable water by 2012 (SFWMD, 2009).

This section will provide a brief description of desalination technology used in the state and
describe some new technologies being tested or recently implemented. It includes a 'walk-
through' of the state's largest seawater desalination facility, a discussion of concentrate

management, and, finally, a general discussion of cost.

3.2 Desalination Processes

Desalination is the removal of salts or dissolved substances from raw water (referred to as
source water) to produce water that is suitable for its intended purpose, for example, human
consumption, irrigation, or industrial use. For the purpose of this report, that intended

purpose is for drinking (potable) water.


April 2010 Page 15 of 109






Florida Department of Environmental Protection, Desalination in Florida

The most common technologies available for desalination around the world are membrane
reverse osmosis (RO), thermal distillation (TD), and electrodialysis (ED). In this section we
will focus on technologies currently in use in Florida, including reverse osmosis, and to a
much lesser extent, electrodialysis. Later, in the discussion of newer technologies, thermal
technologies will be presented, particularly where they are combined with membrane

technologies to produce a hybrid system. While Florida has no existing thermal or distillation
facilities, and they only compose 3% of the production in the U.S.A., they represent more than

40% of the world production.

The chart below (Table 3-1) provides a summary of conventional treatment technologies and
the type of material the technology can remove from the source water. While only a few of

these technologies are capable of removing salts, many are important methods of pre-treating
the raw or source water prior to applying the desalination treatment. Barron (2006) provides
another summary of desalination processes broken down into thermal, solar-driven, and non-
thermal methods (shown in Figure 3-2). Figure 3-2 underscores an important point; some
technologies have been available for some time, but costs to operate the process have deferred

its use. Recent advances in membrane technology and other areas are making these cost-
prohibitive processes more cost effective (Voutchkov, 2008). These include such processes as
membrane distillation or thermal hydrate techniques, which will be described in the new
technology discussion, below.


April 2010 Page 16 of 109







Florida Department of Environmental Protection, Desalination in Florida

Water Treatment Processes Depending on Water Characteristics


0.000001

b 0.001

10

Aqueous Salts

Metal lon
Sugars

Atomic Radius



Ion Exchange

Reverse Osmosis


0.00001

0.01

100


0.0001

0.1

1000


0.001

I

10000


Colloids


0.01

10

100000


Bateria


Latex. Emulsion
Viruses & Protein Cryprospn o. Oocysts Pollens
Asbestos Giardia Cysts


0.1 1

100 1000

1000000 10000000

Small Sand




GAC


'.'-.il f- 1' Eye



Human Hair


Nanofiltraion


Jrri far 391 l I


Microfiltration


r Sand filtration



Srl,.eir ErIrr hlicin

CZril-nlii ri


.i.n 5 Fit- r Filr- .
Screen! S Srr. iiFers

1 Angstrom(Aq = 10" Meter(m) = 1O"Microns(MC) = l1OMiHmeter(mm) G: PVWI.oup SFG phisioph4icallkrra WPpoc

Table 3-1. Filtration Treatment Processes and the Pollutants Removed (Adapted from Frenkel, et al., 2007)


April 2010 Page 17 of 109






Florida Department of Environmental Protection, Desalination in Florida


i u Membrane Ditillafon o

Figure 3-2. A Summary of Water Desalination Processes (Barron, 2006)


Reverse Osmosis

Reverse osmosis (RO) uses pressure to force a solution through a membrane that will hold

solute (waste concentrate) on one side while allowing solvent (potable water) to pass to the

other side. It is the process of applying sufficient pressure to overcome natural osmotic

pressure in order to force water from a region of high salt concentration through a membrane

to a region of low salt concentration. Membranes used in this process are "semi-permeable,"

meaning the membrane will allow solvent (water) to pass, but not solutes such as salt ions. A

more detailed description of RO is provided in Appendix A.

RO removes the broadest range of substances of the three technologies (RO, TD, ED), but in

general it has been energy intensive and the operation and maintenance of the membranes has

been costly. Recent membrane improvements have lowered the costs and improved the

efficiency (NRC, 2008; ADC, 2008; MacHarg, et al., 2008; Voutchkov, 2008; Kucera, 2008;

Fujiwara, 2009).


April 2010 Page 18 of 109






Florida Department of Environmental Protection, Desalination in Florida


Electrodialysis Reversal (EDR)

EDR desalination is a type of membrane process that has been commercially used since the
early 1960s. The Sarasota County "Carlton" plant is the only plant using this form of
desalination in the state. Built in 1995, the facility can generate 12 MGD and is one of the
largest EDR plants in the world. An electric current draws dissolved salt ions through an
electrodialysis stack consisting of alternating layers of cationic and anionic ion exchange
membranes. The result is ion-charged salts and other chemicals are electrically pulled from
the source water to produce the finished water.

Electrodialysis has the lowest energy requirement of the three primary desalination
technologies, but it has inherent limitations. It works best at removing low molecular weight
ionic components from a feed stream. Non-charged, higher molecular weight and less mobile
ionic species will not often be removed. Also, in contrast to RO, electrodialysis becomes less
economical when extremely low salt concentrations in the finished water are required (NRC,
2008).

Distillation

The basic concept of thermal distillation is to heat a saline solution to generate water vapor
and direct the vapor toward a cool surface where it will condense to liquid water. The
condensate is mostly free of the salt. Thermal distillation is the oldest desalination method
used and until recently provided the most worldwide production of water. According the 19th
International Desalination Association plant inventory (GWI, 2006b), in 2006, thermal
distillation technologies represented 43% of the total worldwide desalination capacity.
Membrane technologies accounted for 56% of the capacity. However, it is very energy
intensive and is less efficient at removing volatile substances (i.e. organic compounds,
ammonia, etc). It is most efficient when treating higher salinity source waters. With the cost
of RO-produced water coming down, the use of distillation technology is declining, although
there is renewed interest in combining membrane and distillation technologies (NRC, 2008;
Hsu, et al., 2002; Alklaibi and Lior, 2004; Lawson and Lloyd, 1997; Wong and Dentel, 2009).


April 2010 Page 19 of 109






Florida Department of Environmental Protection, Desalination in Florida


Table 3-2 provides a summary of the characteristics of seawater reverse osmosis and three

forms of thermal desalination technologies: multistage flash (MSF), multiple effect distillation

(MED) with thermal vapor compression (TVC), and mechanical vapor compression (MVC). A

description of these processes is provided in Appendix B. Table 3-3 continues the comparison

for brackish water reverse osmosis, electrodialysis reversal, and nanofiltration (NF).

Nanofiltration is used more as a pretreatment process because it is not effective at removing

salts.


Table 3-2. Comparison of Predominant Seawater Desalination Processes (NRC, 2008)
(Sources: Wangnick, 2002; Trieb, 2007; GWI, 2006a; USBR, 2003; Spiegler and El-Sayed, 1994)

Characteristic Seawater MSF MED MVC
RO (with TVC)

Operating temperature <45 <120 <70 <70
(oC)

Pretreatment High Low Low Very low
requirement

Main energy form Mechanical Steam (heat) Steam (heat Mechanical (electrical) energy
(electrical) and pressure)
energy

Heat consumption NA 250-330 145-390 NA
(kJ/kg)

Electrical energy use 9.5-26 11-19 5.7-9.5 30-57
(kWh/kgal)

Current, typical single < 5,000 < 20,080 < 9,500 < 800
train capacity (kgal/d)

Product water quality 200-500b < 10 < 10 < 10
(TDS mg/1)

Typical water recovery 35-50% 35-45% 35-45% 23-41%

Reliability Moderate Very high Very high High
Reliability Moderate Very high Very high


April 2010 Page 20 of 109







Florida Department of Environmental Protection, Desalination in Florida


Characteristic Brackish water RO ED/EDR NF

Operating temperature <45 <43 <45
(oC)

Pretreatment High Medium High
requirement

Electrical energy use 0.5-3 ~2 kWh/kgal per <1
(kWh/kgal) 1,000 mg/1 of ionic
species removed

Current, typical single < 5,000 < 3,200 < 5,000
train capacity (kgal/d)

Percent ion removal 99-99.5% 50-95% 50-98% removal of
divalent ions; 20-75%
removal of monovalent
ions

Water recovery 50-90% 50-90% 50-90%


RO: Reverse Osmosis oC: Degrees Celsius
ED/EDR: Electrodialysis/Electrodialysis kWh: Kilowatt-hour
Reversal kgal: 1000 gallons
NF: Nanofiltration mg/l: Milligrams per liter
kgal/d: 1000 gallons per day

Table 3-3. Comparison of Predominant Brackish Water Desalination Processes (NRC, 2008)
(Sources: Anne, et al., 2001; Wangnick, 2002; Kiernan and von Gottberg, 1998; Reahl, 2006
Sethi, et al., 2006b; USBR 2003; Semiat, 2008)


April 2010 Page 21 of 109


C: Degrees Celsius
RO: Reverse Osmosis kJ/kg: Kilojoules per kilogram
MSF: Multistage Flash kWh: Kilowatt-hour
MED: Multiple Effect Distillation kgal: 1000 gallons
TVC: Thermal Vapor Compression TDS: Total Dissolved Solids
MVC: Mechanical Vapor Compression mg/l: Milligrams per liter
kgal/d: 1000 gallons per day






Florida Department of Environmental Protection, Desalination in Florida


3.3 Recent Technology

The 2008 National Research Council report, "Desalination: A National Perspective,"
observed that the greatest potential for improvement in the field of desalination technology
will be in reducing the costs to produce the membranes, identifying alternative energy sources
to power the facilities (solar, geothermal, power plant co-location), developing passive
pretreatment systems (in-bank filtration), and developing hybrids of existing technologies or
improvement of old technologies using new developments. An example is the use of
microbial desalination cells that create energy gradients to drive the desalination process (Cao,
et al., 2009; Logan, 2009). Some of the newer technologies are presented below in Table 3-4,
and described in greater detail in Appendix C. Some are in the pilot test stage. All show
promise to reduce the cost of desalination as a means to produce potable water.

Some research efforts around the world provide models for the collaboration of industry,
government, and the research sectors with a common goal of reducing the costs to produce
water through desalination. One such group is the Affordable Desalination Collaboration
(ADC) operating at the US Navy's Seawater Desalination Test Facility at Port Hueneme,
California. At this site various membranes and other associated operational parameters are
tested to determine the optimal process capabilities. The facility serves as a platform on which
cutting edge technologies can be tested and measured for their ability to reduce the overall
cost of the seawater RO treatment process (ADC, 2008).

Another example is the Australian Advanced Membrane Technologies for Water Treatment
Research Cluster. Again, it is a collaborative effort of government, the industry, and
universities (not only from Australia but also from the USA) to improve the use of
nanotechnology, biomimetics and functional materials to deliver new innovations in
membrane technology and cost-effective and highly efficient water recovery systems
(www.csiro.au/partnerships/ps30e.html). This group is also building a national database of
membrane technology that will improve information transfer between researchers and its
practical application.


April 2010 Page 22 of 109






Florida Department of Environmental Protection, Desalination in Florida


These and other organizations such as the American Membrane Technology Association

(AMTA) and the International Desalination Association (IDA) represent examples of efforts to

promote the development and implementation of desalination. Their work not only considers

improvement of the technology but also the minimization of the environmental impacts. It is

important for Florida to stay involved in these efforts.


April 2010 Page 23 of 109







Florida Department of Environmental Protection, Desalination in Florida


Innovation Benefit Citation

Membrane Distillation High theoretical recovery rate (-80%) Dow, et al., 2008; Gunderson, 2008;
Improved membrane Operates at normal pressures reduces cost Hsu, et al., 2002; Banat, et al., 2002;
Hybrid system Waste or low quality heat source can be used Lawson and Lloyd, 1997; Baltutis,
Ability to work with near-saturated solutions 2009; El-Bourawi, et al., 2006; Wong
and Dentel, 2009; Walton, et al., 2004;
Dow, et al., 2008; Furukawa, 2008;
Ludwig, 2004
Forward osmosis Lower energy usage McGinnis & Elimelech, 2007; Cath, et
New chemicals to drive process High feed water recovery al., 2006; Teoh, et al., 2008; Adham, et
Hybrid system Reduced brine discharge al., 2007; McCutcheon, et al., 2006;
Miller and Lindsey, 2006
Clathrate Desalination Operates at low pressures Gunderson, 2008;
"Trap" H20 in CO2 Suitable for all qualities of water sources McCormack and Anderson, 1995;
Recent advance in old technology improved yields Bradshaw, et al., 2006
Nanocomposite Membranes Improved efficiency of extraction Graham-Rowe, 2008; Gunderson,
Thin-film composite membranes with nano-structured Reduced biofouling & maintenance costs by repelling 2008; CSIRO, 2009; Jeong, et al., 2007;
material impurities CNSI/UCLA and NanoH20, LLC.,
Reduced energy needs 2009; Dais Analytic 2009; Risbud,
Longer membrane life 2006
Energy Efficient Pumps Improved consistency of pressure Gunderson, 2008
Axial piston pressure exchanger pump Lower O&M costs Ocean-Pacific Technology, 2008
Rotary type energy recovery device Use of "waste" heat to reduce costs CDWR, 2009b; Stover, 2009a; 2009b;
Stover and Blanco, 2009
Dewvaporation Energy efficient uses recycled energy NRC, 2008
Old technology using newer energy sources Inexpensive to manufacture Hamieh, et al., 2001
"Waste" heat Passive-lower O&M Banat, et al., 2002
Solar Suitable for all qualities of water sources Li, et al., 2006
Freeze Desalination Improved energy efficiency compared to distillation processes Cooley, et al., 2006
Old technique improved by washing of salts Minimal potential for corrosion NRC, 2008
Use of density gradients Little scaling or precipitation

Membrane Vapor Compression Lower operating costs Ruiz, 2005
Similar to membrane distillation Smaller equipment Gunderson, 2008
-Uses compression to reduce temperatures Lower temperatures Dais Analytic, 2009
Use of waste heat Li, et al., 2006
Improved membranes

Table 3-4. Recent Desalination Innovations


April 2010 Page 24 of 109







Florida Department of Environmental Protection, Desalination in Florida


3.4 Key Components of Desalination Process


Primary components of the desalination process include intake and conveyance of raw source

water, water treatment, residuals management, and concentrate disposal. The components of

any desalination system will depend on the source water, the desalting process, and the

disposal option chosen. The example below is the relatively new Tampa Bay Water

desalination facility that came online at the end of 2007 and can produce up to 25 MGD. The

plant is currently one of the largest desalination facilities in the United States. Figure 3-3

illustrates the flow of water through the facility. The source water is from Hillsborough Bay,

where salinities range from 5 to 32 parts per thousand (ppt). It is co-located at a fossil fuel

power plant and uses the heated once-through cooling water to improve the efficiency of the

RO membrane extraction.


Figure 3-3. Flow diagram of the Tampa Bay Water Seawater Desalination Facility (TBW, 2008)


April 2010 Page 25 of 109


Diatomaceous Earth Filters
prte Microscopic materials
Pa e Sand Filters are eliminated
Sett*no t Smaller solid ars r
.'e] ,l 1- ,eI


I z Cartridge Filters ,,
in place to protect
reverse osmosis membranes

Concentrated Salt Water
19 million gallons of concentrated salt water Energy Recoi
are directed back to the power plant. Turbine
mixed with up to 1.4 billion gallons of
cooling water and returned to the discharge canal
then to the bay






Florida Department of Environmental Protection, Desalination in Florida

4M


Figure 3-4. Tampa Bay Water Desalinization Plant (TBW, 2008)

Intakes Structures and Conveyance


Intake and conveyance structures are used to transport source water to the treatment plant.

Site specific source water quality and quantity often influence plant type, intake configuration

and location feasibility. Surface water intake structures must be built to cope with varying

flows, entrainment/impingement issues, and changes in physical, biological, and chemical

characteristics of the influent. Estuarine intakes can potentially see significant changes in

salinity over the tidal cycle. Groundwater influent provides a relatively chemically stable

source of influent. In other words, the chemistry and physical characteristics, like

temperature, in groundwater do not change quickly as surface water does. The groundwater

is less likely to have other substances like organic plant material, algae, zooplankton, but the

geology may restrict the amount of water that can be withdrawn (NRC, 2008; Cooley, at al.,

2006; TWDB, 2008b; CDWR, 2009; Meyerhofer, 2008; Reynolds, 2009).


April 2010 Page 26 of 109






Florida Department of Environmental Protection, Desalination in Florida


Pretreatment

The feed or source water, depending on its origin, may contain various concentrations of

suspended solids and dissolved matter. Therefore, pretreatment is a critical component of all
desalination processes. During the RO process, the volume of feed water decreases, and the
concentration of suspended particles and dissolved ions increases. A comprehensive
pretreatment program will reduce scaling, control corrosion, remove suspended solids and
prevent biological growth. A successfully implemented pretreatment program will ensure

source water has minimal impact on performance of the desalination process.

Depending on the raw water quality, the pretreatment process may consist of all or some of
the following treatment steps:

Removal of large particles using a coarse strainer.
Bio growth control with chlorine or other chemicals.
Clarification with or without coagulation/flocculation.
Clarification and hardness reduction using lime treatment.
Media filtration.
Reduction of alkalinity by pH adjustment.
Addition of scale inhibitor.
Reduction of free chlorine using sodium bisulfite or activated carbon filters.
Water sterilization using UV radiation.
Stabilization basins/chambers to minimize feed variation.

A more detailed description of the pretreatment process for a desalination facility is presented
in Appendix D.

Reverse Osmosis Treatment

The central component of the treatment train is the seawater reverse osmosis (SWRO)

membrane. The Tampa Bay Water system, illustrated in Figure 3-5, is set up so that parallel
trains of RO units can receive maintenance, while other units are operational. The layout of

the membranes provides for easy access for maintenance, removal and replacement. Eight
SWRO membranes sit in each of the 1,176 pressure vessels which comprise the central part of
the desalination system. These are divided into seven separate treatment trains.


April 2010 Page 27 of 109






Florida Department of Environmental Protection, Desalination in Florida

SPost-Treatment

Water from a desalination
W.. I process is typically void of

dissolved solids resulting in
finish water with low hardness

and low alkalinity. As a result,
desalinated water without

post-treatment is corrosive
toward the metal and concrete

surfaces of pipelines and other
wetted surfaces. Without

Figure 3-5. Tampa Desalination Facility Reverse Osmosis proper post-treatment this can
Membranes (TBW, 2008) release metal ions into finished

water and can significantly degrade water-system infrastructure. The introduction of
chemicals such as calcium hydroxide (slaked lime) is used to increase the hardness and

alkalinity, while sodium hydroxide (caustic soda) and carbon dioxide are used to adjust the
pH to stabilize desalinated
water (Figure 3-6). Post-
treatment of desalinated water

is well understood, and

methods for altering
desalinated water are widely
available. Customized post-
treatment and its associated

cost will depend upon factors

such as the chemistry of the
desalinated water and the

complexity of infrastructure
(NRC, 2008). Figure 3-6. Post Treatment Lime Softening Using Slaked Lime


April 2010 Page 28 of 109






Florida Department of Environmental Protection, Desalination in Florida


Concentrate Management
Evaporation Land
Unreported, Ponds,2% Disposal,2% All desalination processes leave behind a
7%
Surface concentrated salt solution that may also
Waters, 41%
Injection contain some pretreatment and process
Wells, 17%/o-- -
residuals. Concentrate and residuals

management involves waste minimization,

treatment, beneficial reuse, and disposal.


Sewers,31%% Each approach has its own set of costs,
benefits, environmental impacts, and
Figure 3-7. A Summary of Desalination Concentrate l ( e A mr
limitations (Sethi, et al., 2006a). A more
Management Methods in the United States
(Adapted from NRC, 2008) detailed discussion of the potential

environmental consequences of concentrate management is presented in Section 4 of this

report. Because of the widely varying level of technology involved in concentrate

management options, and site-specific factors and regulatory considerations that limit

available alternatives, the cost of concentrate management can range from a relatively small

fraction of the cost of the main desalination system to a significant portion of the project cost.


Figure 3-7 illustrates methods of concentrate management based on a survey of the 234

municipal desalination plants in the United States with output greater than 95 m3/day (25,000

gallon per day) (Mickley, 2006). A summary of the challenges and limitations in the current

state of concentrate management methods is also provided in Appendix E.


Offshore Desalination

One recent and unique approach being considered in Florida and elsewhere is a Seawater

Desalination Vessel (SDV).


April 2010 Page 29 of 109







Florida Department of Environmental Protection, Desalination in Florida


h WATER STANDARD
rp W& rr .1 -r


Press Plat
Cotrol Ilom


MVAK, *S*u


Power Genwron
wilh Emisseon Cuoirels

NO ad Ckoruic*a

l""1""-s


Is
~4


t Water


1| ..


n)llfl IYII yi 1) fl i Hlt)lll "ll* If ll*WI


Figure 3-8. Shipboard Desalination (WDR, 2008)

A SDV is a vessel with conventional on-board desalination processes, like reverse osmosis,

that military and cruise ships have used for years. SDV's are typically located offshore where

the water quality is less affected by runoff causing fluctuations in salinity and other water

quality parameters, therefore reducing pre-treatment needs and the costs to desalinate.

Onboard a SDV, as the anchored ship points up-current, seawater is drawn through a passive

intake system near the bow using low-velocity pumps to minimize the impact on sea life.

Discharge water is diffused back into the ocean, from the down-current stern, at a rate

sufficient to maintain the integrity of seawater temperature and salinity (Bluestein, 2008).

Additional information on this project is available at the SJRWMD website:

www.sjr.state.fl.us /coquinacoast/index.html.


Finished water transportation may include seabed pipelines, transfer stations with flex hoses

or shuttle vessels for delivery to on shore storage facilities for distribution.


April 2010 Page 30 of 109


I






Florida Department of Environmental Protection, Desalination in Florida


3.5 Cost

In decades past, the high costs of desalination limited its use in all but a few applications in the
U.S. Today, the cost to desalinate has declined primarily due to increased membrane
efficiency coupled with significant reductions in the cost of membranes. Costs have also been
reduced through improved efficiency of treatment train processes, for example, the use of

waste heat. These declining costs of desalination, coupled with increasing limitations on the
use of fresh groundwater in some parts of the state and the high cost of building pipelines to
transport water from distant well fields to areas of need, have made desalination more
competitive as an alternative source of potable water supply (AWWA, 2008; Henthorne, 2008;
Cooley, et al., 2006; CDWR, 2009; Voutchkov, 2007a; 2007b; Voutchkov, 2008, Heimlich, et al.,

2009).

As the cost for desalination becomes more competitive with conventional water supply costs,
another factor that will affect the cost and ultimately control the final choice of treatment for
the utility, the origin or type of the source water. For example, the specific energy requirement
for RO desalination varies with the treatment system used and the operational conditions, but

the most important factor is generally the concentration of salt in the source water. For
seawater RO, the specific energy usage is typically about 11-26 kWh/kgal with energy
recovery devices (Alonitis, et al., 2003; Miller, 2003; see Table 3-2). For brackish water RO,
energy usage is comparatively lower, about 2-11 kWh/kgal, because the energy required for
desalination is proportional to the feedwater salinity (Sethi, et al., 2006b; see Table 3-3). In

other words, it takes about 2 to 5 times as much energy to treat open ocean water as it does
brackish water. Of course, other site specific factors, such as disposal options, can change the
decision in favor of seawater desalination (NRC, 2008; Voutchkov, 2007b; 2008).

Two recent studies provided a range of Florida specific costs associated with the use of reverse
osmosis membrane technologies. The first study looked at new stand alone systems with
different types of source waters. The study compared relative total costs of RO using brackish
groundwater, brackish surface water, and seawater as the source water (CDM, 2007). The cost

curves associated with each option and are shown in the Figures 3-9, 3-10, and 3-11.


April 2010 Page 31 of 109






Florida Department of Environmental Protection, Desalination in Florida

The basis for the groundwater cost estimates came from the following projects:

City of Clewiston Low Pressure RO Water Treatment Plant, 3.0 MGD.
Lake Region Water Treatment Plant, Palm Beach County, 10 MGD.
Collier County, 12 MGD.
El Paso, Texas, 28 MGD.
Cape Coral, 3.1 MGD.
Lake Worth, 4.5 MGD.
Lee County Pine Woods, 2.3 MGD.
North Miami Beach, 6.5 MGD.
Alameda County Water, 6 MGD.

Fewer projects using seawater as the source water were available for the analysis. The curves
for brackish surface water sources identified no project (as evidenced in Figure 3-10) and were

extrapolated from information on the other projects. The estimated average production cost
per 1,000 gallons from a 10 MGD facility ranges from about $3.20 (brackish groundwater) to
$5.00 (seawater). These cost curves indicate that for all desalination facilities, the larger the
plant, the lower the cost to produce the 1,000 gallons. However, for the brackish groundwater
systems evaluated in the study, the cost differential between large and small facilities was not
as great as it was for the seawater facilities, and remains near the $3.00 to $3.50 range even for
the smaller plants near the 2 MGD production capacity.

As the study states, these figures should only be viewed in the most general way. Every site
has unique factors that can dramatically affect the final production costs, but as previously
noted, the salinity of the source water is a key indicator of energy costs. One of the projects
used in the seawater cost curves is the Tampa Bay Water desalination facility. The costs at this
site probably represent the lower end of the cost range for seawater desalination systems for
two reasons. The source water is estuarine with salinities ranging from 5 to 32 ppt of total
dissolved solids (TDS), lower than the 35 ppt of true seawater, thus requiring less energy to
desalinate. Secondly, the plant is co-located at the TECO Big Bend Power Plant and takes
advantage of the 'waste heat' from the source water to improve efficiency of the membranes,
an existing intake and disposal conveyance system, and proximity to the power grid to reduce
the overall costs to construct and operate. Co-location is an attractive option for those reasons
(Voutchkov, 2007b; 2008; CDWR, 2008a; 2008b).


April 2010 Page 32 of 109













$7.00


$6.00


$5.00


0
$4.00


$3.00


$2.00



$1.00


Florida Department of Environmental Protection, Desalination in Florida


Brackish RO Production Cost












SClewisto N
N Pine
U Lake Worth _____ ier
SCape CcUo
M. g~lon


0 5 10 15

S-ProbableCost --30% -+50% Capacity (MGD)


Figure 3-9. Reverse Osmosis Production Cost Curves Using Brackish Groundwater as the Source

Water (CDM, 2007)


Brackish Surface Water RO Production Cost


$8.00


$7.00


$6. 00



0

$5.00





$200


$1.00


$0.00


5 10 15 20
-Probable Cost -- 30% -+50% Capacity (MGD)


Figure 3-10. Reverse Osmosis Production Cost Curves Using Brackish Surface Water as the Source
Water (CDM, 2007)


April 2010 Page 33 of 109







Florida Department of Environmental Protection, Desalination in Florida


Seawater RO Production Cost


$10.00

$9.00

$8.00

$700

o $6.00

$5.00
0
- $4,00
ri
S$3.00

$2.00

$1.00

$0.00


Windsor


Blue Hills
LADWP
ET pa








0 5 10 15 20 25 30
-Probable Cost -+50% -- 30% Capacity (MGD)


Figure 3-11. Reverse Osmosis Production Cost Curves Using Seawater as the Source Water
(CDM, 2007)


Cost Estimates of Co-Located Desalination Facilities


The second of the two studies, funded by the South Florida Water Management District,

examined the feasibility of co-locating reverse osmosis treatment facilities with electric power

plants (Metcalf & Eddy, 2006). As mentioned previously, this is the approach taken for the

Tampa Bay Water desalination facility, which is co-located at the TECO Big Bend Power

Plant. The heated source water is taken from a small portion of the once-through cooling

water after it has gone through the power plant. The heated source water increases the

efficiency of the membranes to extract the freshwater. The study applied this concept to a

number of potential sites along the southeast and southwest coast of Florida and narrowed the

possibilities to three existing power plant sites. A summary of the estimated construction

costs, O&M costs, and equivalent annual costs is presented in Table 3-5.


April 2010 Page 34 of 109






Florida Department of Environmental Protection, Desalination in Florida


Plant Water Total Total Annual Equiv. Annual
Candidate
Site Capacity Quality Construction Costs O&M Costs Costs
(MGD) (TDS) (mg/l) (millions) (millions) ($/1000 gallons)

Port
or 35 33,000 $275.90 $21.30 $4.16
Everglades


Lauderdale 20 15,000 $148.00 $10.40 $3.88


Fort Myers 10 15,000 $91.10 $6.40 $4.66


Table 3-5. Summary of Estimated Costs to Build and Operate RO Desalination Facilities at Port
Everglades, Lauderdale, and Fort Myers Power Plant Sites (Metcalf & Eddy, 2006)

These cost estimates are slightly higher than at the Tampa Bay Water desalination facility

(probably because the salinity at these sites is higher), but are still in the lower part of the

expected cost curve range for seawater desalination. The low cost is also partly attributable to

co-location on pre-existing industrial sites, which minimizes the costs associated with any new

site development.


Partnership discussions between the Florida Power & Light Company and the Lee County

Utilities, facilitated by the SFWMD, started in early 2003, but no agreement on partnering to

build the seawater desalination facility at the identified Fort Myers site was reached.


3.6 Florida's Membrane Plants

The last segment of this section describes the demographics of desalination facilities in Florida.

The FDEP currently regulates more than 140 Public Water Systems (PWS) that utilize RO

membrane technology in the production of drinking water. These public water systems,

illustrated in Figure 1-4, provide a cumulative capacity in excess of 515 MGD to a population

of greater than 4.2 million (see Table 3-6). The source water for all but three of the systems is

either brackish ground or surface waters. The remaining three seawater systems are the

Tampa Bay Water desalination facility, Marathon, and Stock Island (the latter two are located

in the Florida Keys).


April 2010 Page 35 of 109






Florida Department of Environmental Protection, Desalination in Florida

FDEP RO Plants Population Served Design Capacity
Regulatory (MGD)
District

Northwest 2 < 1000 < 1 MGD

Northeast 15 ~ 240,000 23 MGD

Central 21 -730,000 42 MGD

Southeast 42 -1,985,000 280 MGD

South 31 864,000 81 MGD

Southwest 29 459,000 89 MGD

Totals 140 4,279,000 ~ 515 MGD

Table 3-6. Characterization of Desalination Plants in Florida
(FDEP, 2009)

A complete listing of all FDEP regulated RO plants in Florida may be found in Appendix F.

Figure 3-12, maps the location of the RO plants in the South Florida Water Management

District. They typify the general pattern, statewide; that is, they are located in population

centers, usually along the coastline, where freshwater resources have been depleted and the

costs to transport inland water to the water treatment plant have increased to a point that

using RO technology to treat local brackish water is more cost effective. Figure 3-13 illustrates

the expected growth of potable water supplied by desalination facilities from 2008 to 2025

(SFWMD, 2008a).


April 2010 Page 36 of 109








Florida Department of Environmental Protection, Desalination in Florida


LOWER WEST COAST
Bonita Springs
Cape Coral North
Cape Coral SouLttAist
Clewistbn
Colier County North
Colier County South
Frt Myers
Greater Pine island Assoc.
Island Water Assoatiaon
Lee County Corkscre
Lee County Green Meadows
Lee County North
Lee County Pinewoods .
Marco Island
a* :.-'
,-S ^.4:


I


Desalinatlon Facilties by MGD
t 0-2
* 2-5
S5-10
S10- 15
S15-25

Sseawater

Revised: O111/200


Figure 3-12. 2009 Potable Water Desalination Plants
in the South Florida Water Management District (SFWMD, 2009)


MGD = Millions Gallons per Day


April 2010 Page 37 of 109


UPPER EAST COAST
Fort Pierce
Marti County- North
Martin County- Tropical Farms
Plantation Utilities
Port S Lucie -JEA
Part St Lucie Prineville
Sailfish Point
South Martin Regional
St. Lucie West





LOWER EAST COAST
Deerfield Beach
FKAA Marathon
S FKAA South Dade
S FKAA Stock Island
S Fort Lauderdale Dixe
Kialeah
Highland Beach
Holywod

a Lake Region
Manalapan
S Miramar
North Miami Beach
Seacoast Utilites
S Tequesta






Florida Department of Environmental Protection, Desalination in Florida


S2008


S2025 Projected*
* Based on the 2006/2007WaterSupply Plans


250


200


150
-


| 100 -
50

* 50 -


Lower West
Coast


Upper East
Coast


Kissimmee
Basin


Figure 3-13. Growth of Desalination Potable Water Production in the South Florida Water
Management District (SFWMD, 2008a)

Figure 3-14 provides a summary of the desalination flows and numbers of facilities within the

jurisdiction of the South Florida Water Management District. Clearly there is a significant

increase in facility numbers and flows in the last 20 years and the trend is projected to

continue, as shown in Figure 3-13, particularly along the coastal regions of the District.


April 2010 Page 38 of 109


Lower East
Coast


IZ


!7/






Florida Department of Environmental Protection, Desalination in Florida


* Desalination Capacity (MGD)


* # of Facilities


120


3748
23 3 A
muLL


1985


1990


1995


2000


2005


2012


Figure 3-14. Growth of Desalination in the South Florida Water Management District
(SFWMD, 2008a)


April 2010 Page 39 of 109


1980


I






Florida Department of Environmental Protection, Desalination in Florida


SECTION FOUR: Desalination Concentrate Management


All desalination processes generate a

T concentrated salt or brine by-product
S --- that must be managed in an
environmentally sound manner. The

Importance of its proper management
Swill affect site selection for the facility,

Sthe costs to generate the water, and the
public's acceptance of the project. This
Figure 4-1. Seawater Desalination Plant with Marine public's acceptance of the project. This
Discharge, Perth, Australia section will discuss Florida's regulatory
(http:/ /www.water-technology.net/projects/perth/)
controls, and how they are applied in
the permitting process based on the source water, the desalination technology, and the brine
concentrate management options.

4.1 The Regulations

Section 403.0882, F.S., encourages development of alternative water supplies using
desalination to provide drinking water from lower quality sources that have been previously

underutilized. The statute emphasizes environmental safeguards and efficient regulation
through the development of consistent statewide permitting rules for desalination concentrate
management. Based on this law, the Department has developed specific wastewater
permitting rules for the desalination of seawater, brackish surface water from coastal estuaries
and bays, brackish groundwater pumped from wells, and water from inland rivers. The rules

acknowledge that under certain carefully defined circumstances, concentrate management is
not problematic. They also create a streamlined authorization process for small utilities that
use a desalination process and that present minimal environmental risk.

The rules acknowledge the importance of upfront planning for brine concentrate management:
"During preliminary siting considerations, it is recommended that water supply utilities or
entities that propose to operate demineralization facilities evaluate concentrate disposal
options potentially available in the project area."


April 2010 Page 40 of 109






Florida Department of Environmental Protection, Desalination in Florida

Wastewater permitting rules for concentrate management are found in Chapters 62-620 and
62-4.244, F.A.C. Discharge of concentrate via deep well requires an Underground Injection
Control (UIC) permit from the Department under Chapter 62-528 F.A.C. These rules can be
reviewed at: (http://www.dep.state.fl.us/water/rulesprog.htm#ww).

4.2 Source, Technology, and Management Options

In assessing the potential environmental effects of concentrate management, the three factors
of source water type, desalination technique employed, and the concentrate management
method must be considered. These factors shape the requirements or even the need for a
regulatory permit.

Source waters can be from surface or ground waters, and those waters may be seawater
strength (about 10 to 35 ppt of total dissolved solids) or brackish (from 1 to about 10 ppt).
However, the types of salts found in groundwater are typically different from the salts in
seawater, and this difference can become an issue when the concentrate brine from
groundwater sources is discharged to the ocean or to brackish estuaries. Groundwater source
quality is more chemically stable than surface waters, and ground waters do not typically
contain algae and pathogens, or other biological components that must be removed. Open
ocean seawater quality would generally be much more stable than estuary or river waters,
where quality changes every tidal cycle. These differences in the chemistry of the source water
will influence the desalination process selected (including pretreatment), the composition of
the concentrate, and its management options. For example, a substance like radium, meeting
water quality standards in the source water, may exceed water quality standards in the
concentrate. An accurate chemical characterization of the source water allows the utility to
design the desalination process treatment train and select a suitable management option that
ensures compliance with the water quality standards.

The treatment technology used to reduce the salt content of the source water will affect the

quality of the concentrate. For example, thermal technologies (very common around the
world, but not in Florida) like multi-stage flash distillation, will remove the salt and a number
of other substances, but volatile and many other organic compounds may not be removed.


April 2010 Page 41 of 109






Florida Department of Environmental Protection, Desalination in Florida


Electrodialysis (one facility in Florida) works to remove ionically-charged substances, but will
not remove other 'neutral' or non-charged chemicals like certain organic. Reverse osmosis
(RO) is very effective at removing most substances, most importantly salts. At least a portion
of some chemicals like the ammonium ion, however, may not be as effectively removed by RO
(Koyuncu, et al., 2001). Knowing the treatment technology employed helps the facility owner,
their representatives, and DEP understand what will be in the concentrate and guide the
selection of the most appropriate management option.

The selection of the option will be discussed in greater detail below, but briefly, the facility
owner and their representative should be aware of the volume and composition of the
concentrate. If the final salt content is low then land application options may be available
without affecting vegetation, also called phytotoxicity. If brackish Upper Floridan aquifer
waters were used as the source waters then the plant may be located far from surface waters
and underground injection of the concentrate into a deep saline aquifer may be the best
environmental and economical option available (Heimlich, et al., 2009).

Entrainment of organisms should be evaluated where the facility uses surface water as its

source water. Entrainment is the trapping of organisms in the facility's intake system, by
either drawing the organisms into the treatment facility or impinging or holding the organism
against the screens at the opening of the intake. Typically, the volume withdrawn from the
surface water is a very small part of the source water volume or flow. But occasionally, when
the volume of the intake water is a significant portion of the source water, then entrainment of
organisms can become an issue. Regardless of the intake flow, steps can be taken to minimize
entrainment by locating the intake structures where there is sufficient water to minimize the
impact of the planned withdrawals. The intake structures can also be designed to reduce the
flow velocity providing an opportunity for organisms to escape being drawn into the intake
structure. Screens or booms or both can be used to exclude organisms from the intake. Figure
4-2 below shows a side view of "fish excluder" screen system designed to prevent
impingement (larger organisms becoming trapped against the filtering screens) and
entrainment in this manner.


April 2010 Page 42 of 109







Florida Department of Environmental Protection, Desalination in Florida


FLOW
=i>-
Y :T


Figure 4-2. Side View of a Fish Exclusion Screen around a Surface Water Intake Structure
(NRC, 2008)

The issue of impingement and entrainment can be eliminated in circumstances where it is

possible to use directional drilling to install piping below the seabed and draw water down

through a sandy bottom, rather than pump it from the surface (Meyerhofer, 2008; Reynolds,

2009). This approach also provides some initial filtration as water is drawn down through the

sand, and is illustrated in Figure 4-3, below. The seawater desalination facilities in the Florida

Keys use this approach. Shallow groundwater wells draw in seawater to be conveyed to the

plant's intake.



Drill
Rigd Ocean Surface
and Surface
230 Of
Ocean Floor


Main aquifer / Infiltration
-45 m thick /

Test Slant Well


100 m

Figure 4-3. Directional Drilling to Install Intake Piping Below the Seabed (NRC, 2008)


April 2010 Page 43 of 109


LDWmTllECQtuaAT c- -


- ANMOR






Florida Department of Environmental Protection, Desalination in Florida

4.3 Desalination Concentrate Discharge and Management Options

There are a variety of management methods for handling the desalination concentrate. Some
of the options are:

discharge to sewers for treatment at wastewater treatment plants,
discharge to surface water,
irrigation of crops or landscaping,
land application for aquifer recharge,
deep well injection,
evaporation ponds, and
zero-liquid discharge thermal processes (Davis and Rayman, 2008).

In general, the costs associated with these options are in increasing order with discharge to
sewers being the least expensive (NRC, 2008). A more detailed discussion of the concentrate

management challenges is presented in Appendix E. Two useful informational resources on
the subject are: Jordahl, 2006; and, Mackey and Seacord, 2008.

In Florida, desalination concentrate is primarily discharged to surface waters, land applied,
deep well injected (UIC), or discharged to sanitary sewers. The largest facility in the state, the
Tampa Bay Water desalination plant, discharges to surface waters. The facility draws cooling

water from a power plant and discharges the concentrate back to the power plant where it is
diluted before discharge to Hillsborough Bay (TBW, 2008). Figure 4-4 shows the breakdown
of concentrate management methods in use by active desalination facilities in Florida.


April 2010 Page 44 of 109






Florida Department of Environmental Protection, Desalination in Florida


Figure 4-4. Desalination Concentrate Management Methods in Florida (FDEP, 2008a)

Figure 3-7 in Section 3 of this report provides a similar pie chart showing the distribution of
concentrate management in the United States. There are distinct differences between these
two figures that demonstrate the uniqueness of Florida's environmental setting compared to
the rest of the country. Nationally, land application, for example, accounts for only 2%, but
represents about 34% in Florida. This is a reflection of the low salinity of the source water and
the chemical composition being more suitable for blending and land application, as well as the
importance of water reuse in the state compared to most other states in the country (Bryck, et
al., 2008). The geologic setting of Florida permits a greater use of injection wells (almost twice
the national average).

Discharge to Domestic Wastewater Treatment Collection Systems

Approximately 20% of desalination facilities discharge their concentrate to permitted domestic
(i.e. sanitary) wastewater treatment plants (WWTP). These RO facilities are typically smaller,
or their concentrate contains low levels of salt, or both. This option depends on the ability and
willingness of the WWTP to accept the saline discharge and continue to meet the requirements


April 2010 Page 45 of 109


Permitted Desalination Concentration Dischargers




9% 18% m Discharge to Sanitary
Sewer
m Land Application

UIC/Deep Well
Injection
m Direct Surface Water
Discharge
26% Combination (Other)
31%






Florida Department of Environmental Protection, Desalination in Florida


of its own discharge permit. Water treatment plants that discharge concentrate to domestic
facilities are considered industrial discharges and must meet pretreatment requirements
established by the domestic wastewater utility. A receiving wastewater treatment facility is
primarily concerned about the concentrate characteristics in order to determine the salt content
in the influent to the WWTP. Too high a salt content will affect the plant's treatment efficiency

and can possibly damage the biological elements of the treatment process. If the wastewater
facility discharges to surface water, these desalination plants are classed as Industrial Users
and may be subject to federal industrial pretreatment requirements imposed by the utility
under the Clean Water Act (CWA) (33 U.S.C. 1251 et seq., 1972). If the WWTP facility applies
reclaimed water to land they must make sure the effluent salt concentration does not cause
plant damage.

The concentrate may by-pass the wastewater facility and be post-blended with treated
domestic wastewater effluent before the effluent is discharged to surface water, land applied,
or injected underground. These options provide dilution of the concentrate, reducing
environmental issues related to elevated minerals, whole effluent toxicity, or ionic imbalance

toxicity.

The post-blending method would require the domestic facility to revise its National Pollutant
Discharge Elimination System (NPDES) permit to account for the changes in its discharge
composition associated with the addition of the demineralization concentrate. These
permitting options are addressed in Rule 62-620.625(6), F.A.C., (previously referenced). The
Department worked with SJRWMD to map out the wastewater permitting process for
desalination and demineralization water treatment plants. The NPDES Wastewater permit
and other state and federal permit programs are discussed in SJRWMD reports and technical
memoranda and can be accessed at http:/ / sjr.state.fl.us / technicalreports/pdfs / SP / ST2006-
SPl.pdf (R. W. Beck, Inc., et al., 2006).

Direct Surface Water Discharge

Surface water discharges are regulated under the federal Clean Water Act through the NPDES
permitting program. USEPA has authorized the Department to administer the program and


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Florida Department of Environmental Protection, Desalination in Florida


issue NPDES permits. Therefore, any proposed surface water discharge would be required to

apply to the Department for an individual NPDES permit prior to commencement of any
discharge.

Approximately 18% of desalination facilities in Florida discharge concentrate to surface water.
The surface water may be the Atlantic Ocean or Gulf of Mexico, coastal estuaries, freshwater
lakes or rivers, or to storm water management systems that discharge to surface waters. Each
of these potential locations poses it own unique set of technical and environmental issues.
Typically, demineralization concentrate has a higher salinity than the receiving water. This
may result in exceedences of water quality standards, including aquatic toxicity (Danoun,
2007).

Exceedences of water quality standards caused by the higher salinity of the concentrate
discharge can sometimes be mitigated by using special discharge piping systems called
diffusers, which allow the effluent to mix more quickly with the receiving water. There are
also situations where the source water quality has a different chemical composition than the
receiving water. For example, a brackish, groundwater source water may have a different
ratio of minerals than a receiving seawater environment. The salt ratio of the concentrate is
different than the receiving waters or 'ionically imbalanced'. Where appropriate, mixing zones
can be granted in the vicinity of the outfall (Rule 62-4.244(3)(d), F.A.C.;
http://www.dep.state.fl.us/water/rulesprog.htm#ww). Diffuser systems are a commonly
used technology for a variety of wastewater applications worldwide. The image below shows
an example of a section of piping for a wastewater effluent diffuser system.


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Florida Department of Environmental Protection, Desalination in Florida


I%

















Figure 4-5. Example of an Effluent Diffuser System (Not Associated with a Desalination Project)
(Dayton & Knight, Ltd., Vancouver, BC, Canada. 2008)

The St. Johns River Water Management District and the South Florida Water Management
District have supported several studies to look at the feasibility of siting desalination facilities
in their districts (R.W. Beck, Inc., et al., 2006; Metcalf & Eddy, et al., 2006). Several SJRWMD
publications examined the feasibility of ocean outfalls of desalination concentrate (CH2M
HILL, 2005a; 2005b), the feasibility and limiting problems associated with locating a
desalination discharge on the Indian River Lagoon (R.W. Beck, Inc., et al., 2006), and the
feasibility of locating a facility along the St. Johns River, on the southern shore of Lake Monroe
(CH2M HILL, 2004). In the last part of this section of the report, a more detailed discussion
will be presented of environmental issues of concentrate in the receiving water.

Land Application and Blending with Reclaimed Water for Recharge and Irrigation

Approximately 29% of desalination concentrate is land applied, frequently by blending with
reclaimed water for recharge and irrigation. Reclaimed water is the term used for domestic
wastewater treated to levels that allow it to be reused in various ways. Reclaimed water is
used for irrigation, for example, in lieu of using drinking water, thus preserving groundwater
and fresh surface water resources for human consumption. Florida's regulations for reuse of


April 2010 Page 48 of 109







Florida Department of Environmental Protection, Desalination in Florida


reclaimed water and desalination concentrate management have detailed requirements to

ensure public health and safety and to meet water quality standards (Chapter 62-620, F.A.C.,

Wastewater Facility Permitting and Chapter 62-610, F.A.C., Reuse of Reclaimed Water and

Land Application http:/ /www.dep.state.fl.us /water/rulesprog.htm#ww).


The Department rule also establishes mixing formulas to make sure the concentrate blended

with the reclaimed water and discharged to land application will have a relatively low salinity.

Saline tolerant vegetation may be needed in order to maintain proper ground cover. As

mentioned earlier, the relatively large percentage of reuse of desalination concentrate used in

the state is a reflection of the low salinity of the source waters used in many of the RO plants in


FIGURE 1. A TYPICAL CLASS I INJECTION WELL

Injecion Injected Fluid
Pressure
Gauge
::uge Valves
Annulus
Pressure Annular
Gauge Access

ae./el -- :1--L - --
. .. .
".: ", . ,." ':;, .:": : ..' " .0 ".. .0 .;.
















S0 jection Interval




Figure 4-6 An Idealized Cross-section of an
--------- ~An nulus -- -











Underground Injection Control Well
(FDEP, 2008c)


Florida. Lower mineral content in the

concentrate provide the utility with more

opportunities to directly use the water for

irrigation or for blending with reclaimed water

for land application. In Florida this is especially

true, where more than 600 MGD of reclaimed

water is used.


Deep Well Injection

Approximately 33% of desalination concentrate

in Florida is discharged to specially designed

and constructed deep wells permitted through

the Underground Injection Control (UIC)

program, in Chapter 62-528, F.A.C.

(http://www.dep.state.fl.us/water/rulesprog.h

tm#ww).


Deep well injection or Class I well systems

essentially operate by injecting the concentrate


stream below at least one confining geologic layer. The salty nature of the concentrate helps it

blend with the saline waters of the injection zone (Heimlich, et al., 2009). Concentrate can also


April 2010 Page 49 of 109






Florida Department of Environmental Protection, Desalination in Florida


be blended with other industrial wastewater or with treated domestic wastewater at
wastewater facilities that use Class I wells, but typically that would require the municipality to
upgrade the injection well to handle the more corrosive nature of a brine discharge. If the
concentrate enters the wastewater facility through the collection system or at the headworks of
the wastewater plant, then the effluent is considered domestic wastewater and the well will
not need to be upgraded.

The SJRWMD has looked at the potential for using Underground Injection Control (UIC) Class
V wells for disposal of RO concentrate along the coasts of Flagler, Brevard, and Indian River
Counties (L.S. Sims & Associates, Inc., 2006; CH2M HILL, 2008). Unlike the Class I deep wells,
Class V UIC wells do not need to be injected into a confined aquifer, and the well depth can be
shallower and less expensive to construct. However, the lack of confinement means the water
quality of the injectate must meet drinking water quality standards where the receiving
groundwater is an Underground Source of Drinking Water (USDW). Groundwater containing
concentrations of TDS greater 10,000 mg/1 is not considered potable water or an USDW.
Treatment standards for discharge into such waters are reduced, such as in the Florida Keys.

The purpose of the SJRWMD studies was to determine if there were high TDS zones in the
coastal counties where the shallower Class V wells would be feasible. Based on the available
groundwater data it appears that the ocean side of the coastal barrier islands in Flagler County
and the southern coastal portion of Indian River County would offer the greatest potential for
Class V wells. The study suggests an exploratory drilling program to better delineate the
brackish-saline water interface along the barrier islands to site pilot Class V wells.


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Florida Department of Environmental Protection, Desalination in Florida


Bn rdmpl Bay Swalie Desalirnjoin Plant
POW rPlo t Fif,. i f ; -d iri, ',,,, i r ,ir ,, ,i ; ir,. .Io land
B.ulnding Fadl Ibs



Prelrealmeni





Figure 4-7. Process Overview for Co-Location of a Desalination Plant and Steam Electric Power
Plant (NRC, 2008)

Concentrate Blending at Co-located Coastal Electric Power Plants

A surface water discharge method used in Florida is the co-location of a desalination facility

with an existing power plant. The Tampa Bay Water desalination facility is an example of this

approach and became fully operational in December 2007. Co-location is practical for power

plants with once-through cooling water systems, described as follows. Once-through cooling

water systems are located adjacent to coastal surface waters, rivers and lakes. The power

plants pump very large quantities of surface water through their cooling systems and return

nearly all the water to the source. In the co-location scenario, a portion of the cooling water,

once heated, is used for desalination and the concentrate is returned to the cooling water

stream before its discharge back to the surface water. At the Tampa site, approximately 44

MGD of saltwater is drawn from the heated effluent and processed through the RO facility.

Up to 25 MGD of potable water is generated and 19 MGD of brine concentrate is returned

downstream of the RO source water intake, where it blends with about 1000 MGD of cooling

water before entering Hillsborough Bay (TBW, 2008). Just to the north of the Tampa site, the

City of Tarpon Springs is planning a 6.4 MGD RO plant that offers a slight variation of this

approach (Robert, et al., 2009). Brackish groundwater will be the source water and concentrate

disposal will be to a nearby power plant cooling water discharge canal.


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Florida Department of Environmental Protection, Desalination in Florida

Combining a desalination treatment plant with a once-
through cooling water system offers the cost-saving
advantage of utilizing existing permitted intake and
discharge structures (Voutchkov, 2007b; 2008).
However, once-through cooling water power plants in
Florida are generally located in coastal bays and
estuaries where environmental issues must be
addressed in order for discharge to be feasible.

The SJRWMD conducted a feasibility study for the co-
location of a desalination facility with an existing

power plant that utilizes the Indian River Lagoon as a
once-through cooling water source and discharge
destination. Modeling of the projected discharges

Figure 4-8. Aerial View of a showed that the poor circulation patterns in the
Desalination Plant (foreground) Co- lagoon, at the chosen locations, would have resulted in
Located with a Steam Electric Power
Plant (background) the buildup of salts and significant environmental
(TBW, 2008)
impacts. Therefore it was not a recommended site for
locating a large-scale desalination facility, although small-scale facilities could be feasible
(R.W. Beck, Inc., et al., 2006).

Similarly, the SFWMD examined potential co-locations in its jurisdictional area (Metcalf &
Eddy, 2006; VandeVenter, et al., 2008). Using technical, regulatory, and socioeconomic
feasibility as screening tools, candidate sites were reduced to three locations (Ft. Myers,
Lauderdale, and Port Everglades) that were recommended for further evaluation, including
conceptual design and specifications for a pilot study.

Desalination facilities may also be co-located at coastal or estuarine municipal wastewater
facilities, where the blended effluent would mix better in the brackish or marine environment
and the two waste stream characteristics would be diluted. For example, the salt of the
concentrate would be diluted by the freshwater of the municipal wastewater, and the nutrients
of the wastewater would be diluted by the low nutrient concentrate. An example of this type


April 2010 Page 52 of 109






Florida Department of Environmental Protection, Desalination in Florida

of arrangement is the City of Hollywood, where the city-owned utility's water treatment RO

plant treats brackish groundwater and blends the concentrate stream with the utility

wastewater prior to entering the utility's ocean outfall (City of Hollywood, 2009).

HOLLYWOOD WATER TREATMENT PLANT














.... ........., .


Figure 4-9. Illustration of the City of Hollywood Water Treatment Plant using a Combination of
Reverse Osmosis and Nanofiltration to Treat Source Waters from Two Aquifers
(City of Hollywood, 2009)

Another example is currently under construction in Deerfield Beach where the concentrate

from the nanofiltration plant is recovered by blending it with additional Florida aquifer water

and fed to a new 3 MGD RO plant for further treatment (SFWMD, 2009).

4.4 Potential Environmental Issues for Surface Water Discharges

There are currently 46 NPDES surface water discharge permits for desalination and

demineralization water treatment plants in Florida (FDEP, 2008b). Many of these have been in

operation for a number of years. From the data collected at these sites we can provide some

insight as to the potential environmental problems any one site may experience. Some of the

environmental concerns have already been discussed in this section. UIC injectate must meet

primary and secondary drinking water standards if the injection zone is in an Underground

Source of Drinking Water (USDW) (<10,000 mg/1 TDS). The applicant can seek water quality

exemptions for the secondary standards, but must meet the primary drinking water quality

standards. Land application of concentrate must not be phytotoxic or have a high enough salt


April 2010 Page 53 of 109






Florida Department of Environmental Protection, Desalination in Florida

content to harm the vegetation receiving the irrigation water. Disposal to collection systems
must not affect the biological integrity of the wastewater treatment facility. Where intake
waters are drawn from surface waters, attention must be given to minimizing entrainment of
the surface water organisms.

The remainder of this discussion will focus further on environmental issues associated with

concentrate discharged to surface waters. Concentrate will be presented as two primary
components, the major salt groups (for example, sodium, chloride, sulfate, calcium,
magnesium) and other parameters (for example, nutrients, metals, and organics. Either

group, when discharged into surface waters must not cause toxicity or impact the biological
community of the receiving waters.

The environmental impact from the major salts is related to the absolute or total concentration

of salt, measured as TDS or total salinity measured in ppt, or the composition or ratio of the
salts.

If the source water used is the same as the receiving water, like at the Tampa Bay Water

desalination facility, where estuarine water is both the source water and the receiving water,

the specific salts will be in the same ratio. In this situation, the concern is the total salt content.
If the concentrate's salinity is too high it becomes toxic to plants and animals in the receiving

water environment. How high is too high depends on the receiving water's salinity. In
estuary or open ocean water, the ambient salinity can range from 15 to 35 ppt. In this setting,
desalination concentrate exceeding 40 ppt can cause an unacceptable impact to the ecology of

the receiving water. Site specific analysis is needed to determine the amount of dilution
needed to bring the final discharge salinity into an acceptable range for the receiving water.

If the source water comes from a different source than the receiving water, for example, a

groundwater source water is used and the concentrate is discharged into a brackish surface
water like an estuary, the final salt content of the discharge may be lower than the estuary or

even the same, but the ratio or type of salts is different than those of the estuary. The estuary
salt is dominated by sodium and chloride and the groundwater by calcium and sulfates. The
discharge is said to be 'ionically imbalanced' and can cause toxicity. It is toxic because the


April 2010 Page 54 of 109






Florida Department of Environmental Protection, Desalination in Florida

organisms in the receiving water are accustomed to this ratio of salts. A shift in the ratio can
cause an osmotic imbalance and toxicity. A site specific analysis is needed to determine if
there is toxicity and, if so, what steps would need to be taken to minimize the impact of the salt
imbalance. Fortunately, the major salts in brackish water do not bioaccumulate or biomagnify
in the receiving water food chain like some substances such as lead and mercury. In fact,

several, like calcium, are building blocks for the plants and animals. Therefore, the focus in
dealing with ionically imbalanced concentrates is to provide an initial dilution.

Circulation

Another consideration related to the salt content of the concentrate is salt buildup or
accumulation in the receiving waters. Even where the concentrate salinity is not toxic, poor

circulation of the receiving water may limit flushing of the system and the salt content will
increase over time to a point where it is toxic to the ecological community. If the source water
is from the same water body, the change will be accelerated. The more complex the flow
patterns in the receiving waters the more difficult and costly it is to demonstrate that no
accumulation of salt occurs. In the case of the Tampa Bay Water desalination facility, the

complex water movements in Hillsborough Bay required the use of sophisticated near field
and far field models to show no impact.

The SJRWMD identified several types of possible adverse effects of desalination on a brackish
estuary in its 2006 report titled Evaluation of Potential Impacts of Demineralization Concentrate
Discharge to the Indian River Lagoon (Study). The study focused on co-location of a desalination

plant with power plants in Brevard County in a portion of the Indian River Lagoon near
Titusville, and used long-term water quality modeling to evaluate potential changes to the
lagoon based on a co-located desalination plant. Although this study was a preliminary look
at possible effects using computer models, it provides some insight into the types of concerns
that need to be addressed in a semi-enclosed tidal estuary typical of much of the Florida
coastline.

The study showed a long-term increase in salinity and decrease in seagrass, which provides

the major habitat for juvenile gamefish, baitfish and crustaceans within the lagoon. Significant


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Florida Department of Environmental Protection, Desalination in Florida

decreases in the number of the species were also predicted. According to the study, these
effects would not be confined to the vicinity of the concentrate discharge, but would be more
widespread throughout large areas of the lagoon.

Discharge in an open ocean environment, however, was shown in other SJRWMD reports to
have less adverse impacts, depending on the location and design of the discharge system

(CH2M HILL, 2005a; CH2M HILL 2005b; R.W. Beck, Inc., et al., 2006).

Dissolved Oxygen

Dissolved oxygen levels in the water can also have an impact on the aquatic environment
surrounding the discharge location. Where temperature and/or salinity changes have resulted
in the water column becoming stratified, or layered, oxygen may not be able to diffuse from

the near-surface to deeper layers. This leads to decreased levels of dissolved oxygen in these
deeper layers, which could have negative effects on the respiration of the organisms present
there. Less mobile or non-mobile organisms such as juvenile fish and clams are most affected
by this drop in dissolved oxygen. This can also impact other animals that depend on them as
food source (R.W. Beck, Inc. et. al, 2006).

The stratification resulting from poorly dispersed concentrate into the receiving water can
result in damage to the benthic or bottom community, including the seagrasses (Gacia, et al.,
2007; Perez Talavera and Quesada Ruiz, 2001; Pilar Ruso, et al., 2007).

Other Parameters

The SJRWMD ocean outfall discharge feasibility study used Indian River Lagoon water as the
source water and used a pilot RO facility to determine what parameters may be of concern.
Looking at more than 160 parameters (nutrients, metals, radiologicals, volatile organic,
toxicity and others), researchers found fluoride and copper to be of concern in Class II shellfish
waters, and only copper to be of concern in Class III recreational waters (Reiss Environmental,

Inc., 2003a; 2003b). A mixing zone could be used to bring these parameters into compliance.


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Florida Department of Environmental Protection, Desalination in Florida


At other locations in Florida, radiologicals like radium and nutrients like ammonia were

present at acceptable levels in the source water, but exceeded water quality standards in the

concentrate.


Another potential source of contaminants in the concentrate is from chemicals used in the

operation and maintenance of the desalination facility (NRC, 2008). These include cleaning

and conditioning reagents, anti-scaleant chemicals, and metals generated from corrosion of

piping (iron, chromium, and nickel). Table 4-1 summarizes the types of pretreatment

chemicals used to condition the source waters and Table 4-2 summarizes the typical cleaning

formulations used in the maintenance of nanofiltration and RO membranes. Some chemicals

like chlorine can combine with organic materials and form another group of chemicals,

disinfection by-products such as total trihalomethane, that must be evaluated (Agus, et al.,

2009).


Reported
Chemical Additive Dosing References
(mg/l)
Abart, 1993; Redondo and Lomax, 1997;
Chlorine 0.5-6 Morton, et al., 1997; Woodward Clyde
Consultants, 1991

Morton, et al., 1997; Redondo and
Sodium bisulfate 3-19 Lomax, 1997; Woodward Clyde
Consultants, 1991

Ferric chloride 0.8-25 Baig and Kubti, 1998; Woodward Clyde
Ferric chloride 0.8-25 Consultants, 1
Consultants, 1991

Polyelecrolyte 0.2-4 Ebrahim, et al., 1995; DuPont, 1994;
Polyelectrolyte 0.2-4
Hussain and Ahmed, 1998

Sulfuc Ad 6.6- Al-Shammiri, et al., 2000; Morton, et al.,
Sulfuric Acid 6.6-100
1996; Al-Amad and Aleem, 1993

Sodium Al-Ahmad and Aleem, 1993; Al-
Hexametaphosphate 2-10
Hexe 20 Shammiri, et al., 2000; FilmTec, 2000
(SHMP)

Polyacrylic acid 2.9 Woodward Clyde Consultants, 1991

Phosphonate 1.4 Al-Shammiri, et al., 2000

Table 4-1. Reported Dosing Concentrations of Pretreatment Chemical Additives in Reverse
Osmosis Desalination (NRC, 2008)


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Florida Department of Environmental Protection, Desalination in Florida

Foulant Type Cleaning Solutions

Inorganic saltsa 0.2% HCI
0.5% H3P04
2% citric acid
Metal oxides 2% citric acid
1% Na2S204
Inorganic colloids (silt) 0.1% NaOH, 0.05 % Na dodecyl benzene
sulfonate, pH 12
Silica (and metal silicates) Ammonium bifluoride
0.1% NaOH, 0.05 % Na dodecyl benzene
sulfonate, pH 12
Biofilms and organic Hypochlorite, hydrogen peroxide, 0.1%
NaOH, 0.05% Na dodecyl benzene
sulfonate, pH 12
1% sodium triphosphate, 1% trisodium
phosphate, 1% sodium EDTA
aBarium sulfate, calcium carbonate, calcium sulfate

Table 4-2. Typical Nanoflitration and Reverse Osmosis Cleaning Formulations (NRC, 2008)


Desalination water treatment facilities have been permitted and operated in Florida since the

1970's. The Department has a well-developed regulatory process for ensuring that utilities

have the opportunity to expand and develop new desalination facilities in the state, and that

the concentrate can be managed to protect Florida's water resources, including natural

systems. Desalination utilities have been permitted to implement a broad range concentrate

management options. Forty-six facilities, for example, discharge concentrate to surface water

under NPDES permits issued by the Department in full compliance with the federal Clean

Water Act. Many others, the majority of demineralization facilities, discharge either to land

application and deep wells, or discharge to domestic wastewater facilities for treatment. The

options often incorporate blending with reclaimed water for recharge and irrigation. This

large number of facilities and the diversity of concentrate management scenarios demonstrate

the effectiveness of Florida's regulatory approach and adaptability of Florida's public water

supply utilities.


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Florida Department of Environmental Protection, Desalination in Florida


SECTION FIVE: Conclusions


Florida is the national leader in the application of desalination, in the number of
projects and the volume of potable water generated by the technology.

Given the large numbers of desalination plants in Florida, and the anticipated
development of new facilities over the next 10 years, desalination has been proven
to be a feasible and cost-effective source of supply for many utilities. While
technological improvements and cost-sharing could hasten the wider application of
desalination technology, it is clear that few barriers now exist for its expanded use
in the state.

Thermal Distillation, while a dominant technology in the world, is a minor
component of the U.S. desalination and non-existent in Florida. The primary
reason is energy needs compared to other technologies. Reverse Osmosis is by far
the dominant technology used in the state. This may change as technology
provides new options.

Finite water resources in Florida provide the major incentive for aggressive water
conservation and the need to develop alternative water resources, including reuse
of treated wastewater and storm water, desalination, water conservation, and
Underground Injection Control (UIC) Aquifer Storage and Recovery (ASR)
systems and above ground reservoirs.

The 2005 Legislature created the Water Protection and Sustainability Program to
encourage and partially fund the development of alternative water supplies to meet
the future potable water needs of the state. In the first three years of the program
(2005-2008), the program provided funding assistance for the construction of 344
projects. Of these, brackish water desalination projects are expected to provide 234


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Florida Department of Environmental Protection, Desalination in Florida
million gallons of potable water per day. Continued funding of the program would
provide additional incentive for the development of alternative water supplies in
Florida, including desalination.

* The costs associated with desalination can vanr greatly depending on the source
water, typically increasing in cost when moving from the use of brackish
groundwater to open seawater. However, the costs for environmentally safe
disposal at some locations may offset the cost savings of using of lower-salinity
source water. Co-location at steam electric power plants or large municipal
wastewater treatment plants can reduce the energy, capital and operational costs.

* Use of new technology (nanotechnology, energy efficient pumps, alternative energy
sources, use of 'waste heat') should continue to reduce the costs to operate and
maintain desalination processes like membrane filtration and, equally important,
reduce the carbon footprint.

* Technology transfer is vital for government agencies and utilities in Florida.
Partnering with existing desalination organizations, such as the American
Membrane Technology Association (AMTA), Affordable Desalination
Collaboration (ADC), WaterReuse Foundation, and International Desalination
Association (IDA), is needed to remain abreast of innovative technologies and to
exchange 'lessons learned'.

* Similar to technology transfer, an exchange of information is needed on
environmental issues associated with desalination. This information would help to
minimize the potential risks associated with development of new desalination
facilities.


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Florida Department of Environmental Protection, Desalination in Florida


REFERENCES


Affordable Desalination Collaboration (ADC). 2008. "Affordable Desalination Profiles State of the Art
SWRO".
http://www.affordabledesal.com/home/news/ADC % 20Completes % 20Profile % 20of% 20SWRO % 203
-28-08.pdf

American I V1tcr Works Association (AVWVA). 2008. Desalination. "Florida 2030 A Vision for
Sustainable I\ water Infrastructure". Florida Section American I\ water Works Association. September,
2008. Lisa Henthorne, Chairperson.
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Abart, E. 1993. "Decision-making Strategy for Handling Biocides: Experience at Yuma Desalting
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Adham, S., Oppenheimer, J., Liu, L., and Kumar, M. 2007. "Dewatering Reverse Osmosis Concentrate
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Akpoji, A. 2009. "Concentrate Management: South Florida Challenges". Presented at the Florida
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Akpoji, A., M.E. Elsner, M.G. Craig, P. Nicholas, and B. Ross. 2009. South Florida Embraces
Desalination and Reuse for the Future. International Desalination and 1"Vater Reuse,
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Alonitis, S.A., Kouroumbas, K., and Vlachakis, N. 2003. "Energy Consumption and Membrane
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Al-Shammiri, M., Safar, M., and Al-Dawa, M. 2000. "Evaluation of Two Different Antiscalants in
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Baig, M. and Kutbi, A. A. A. 1998. "Design Features of a 20 MGD SWRO Desalination Plant, Al
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Baltutis, E. 2009. High Performance Membrane Distillation (PHMD) Moves from the Pilot to
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Banat, F., Jumah, R. and Garaibeh, M. 2002. "Exploitation of Solar Energy Collected by Solar Stills
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Barron, O. 2006. Desalination Options and their possible implementation in Western Australia:
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Birkett, J. 2003. Desalination Activities in England during the Later 17th Century. International
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Desalination Report Vol. 44(36). October, 2008.

Wilson, G. 2001. Desalination of Sea I Vator. Monticello Research Report. Monticello, Virginia.

Wong, E. and Dentel, S. K. 2009. "Direct Contact Membrane Distillation of Brackish and
Contaminated V1htcr Sources for Sourcing Potable Il'tcr". USGS Project ID: 2008DE130B.
February 2009.

Woodward Clyde Consultants. 1991. Final Environmental Impact Report (FEIR). City of Santa
Barbara and Ionics, Incorporated's Temporary Emergency Desalination Project, SB-106-90. State
Clearing House No. 9010859.


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Florida Department of Environmental Protection, Desalination in Florida

APPENDIXA: Reverse Osmosis (RO) Membrane Technologies


ia\7at is osmosis?

Osmosis is a natural process involving fluid flow across a semi-permeable membrane barrier.
Consider a tank of pure water with a semi-permeable membrane dividing it into two sides.
Pure water in contact with both sides of the membrane at equal pressure and temperature has
no net flow across the membrane because the "chemical potential" is equal on both sides. If
salt is added on one side, osmoticc pressure" will cause flow from the pure water side across
the membrane to the salt solution side. This will continue until the equilibrium of chemical
potential is restored. In scientific terms, the two sides of the tank have a difference in their
"chemical potentials," and the solution equalizes its chemical potential by osmosis.

I\7hait is a semi-permeable membrane?

Semi-permeable refers to a membrane that selectively allows certain substances to pass
through it while retaining others. In actuality, many things will pass through the membrane
but at significantly different rates. In reverse osmosis (RO), the solvent (water) passes through
the membrane at a much faster rate than the dissolved solids (salts). The net effect is that a
solute-solvent separation occurs, with pure water being the product.

Reverse Osmosis

In reverse osmosis, the freshwater water molecule, under high pressure, moves in the opposite
direction or 'reverse' direction than would occur normally. The high pressure will raise the
chemical potential of the water in the salt solution and cause a solvent or in our case a
freshwater flow to the pure water side, because it now has a lower chemical potential. This
phenomenon is called reverse osmosis.


The driving force of the reverse osmosis process is applied pressure. The amount of energy
required for osmotic separation is directly related to the salinity of the solution. Thus, less
energy is required to produce the same amount of water from brackish water than the saltier
seawater. This is an important point because as the source increases in salinity, the higher the
pressure needed to produce the potable water, the greater the energy needs, and the higher the


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cost. The pressure needed to be exerted on the high solute side of the membrane, ranges from
30-250 pounds per square inch (psi) when the source water is fresh and brackish water, to 600-
1000 psi for seawater (Hydranautics, 2001b).

There are three major groups of polymeric materials which can be used to produce satisfactory
reverse osmosis membranes: cellulose acetate (CAB), composite polyamide (CPA), and thin-
film composite. Depending upon the polymeric material composition of the membrane, the
manufacturing process, operating conditions and performance of the membrane will differ
significantly. Research on reverse osmosis began in the 1950's when the first membranes were
made of cellulose acetate. The costs to make, operate and maintain these membranes restricted
their application, until the early 1980's, when research in U.S. resulted in the first composite

polyamide membrane. This membrane had significantly higher permeate flow and salt
rejection than cellulosic membranes. Since then, improvements in materials and their
configuration have further reduced costs and improved the strength and resiliency to
changing temperatures and pH.

Cellulose Acetate Membranes

The original cellulose acetate membrane, developed in the late 1950's by Loeb and Sourirajan,
was made from the cellulose diacetate polymer. Currently, cellulose acetate membranes are
usually made from a blend of cellulose diacetate and triacetate. The membrane is formed by
casting a thin film of acetone-based solution, comprised of the cellulose acetate polymer with
swelling additives, onto a non-woven polyester fabric. After the initial casting, two additional
steps, including a cold bath followed by high temperature annealing, complete the membrane
formation process.

Cellulose acetate membranes are inexpensive and easy to manufacture but suffer from several
limitations. One such limitation is that their asymmetric structure makes them susceptible to

compaction under high operating pressures, especially at elevated temperatures. Compaction
occurs when the thin dense layer of the membrane thickens by merging with the thicker
porous substructure, leading to a reduction in product flux.


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Other common limitations of cellulose acetate membranes include:

Are susceptible to hydrolysis;
Can only be used over a limited pH range (low pH 3 to 5 and high pH 6 to 8, depending
on the manufacturers);
Undergo degradation at temperatures above 35C;
Are vulnerable to attack by bacteria; and
Have high water permeability but reject low molecular weight contaminants poorly.

In comparison, cellulose triacetate membranes have advantages such as improved salt
rejection characteristics and reduced susceptibility to pH, high temperature and microbial
attack. However, cellulose triacetate membranes have a lower water permeability than
cellulose acetate membranes. Blends of cellulose triacetate and cellulose acetate have been

developed to take advantage of the desirable characteristics of both membranes.


Composite Polyamide Membranes

Composite polyamide membranes are manufactured in two distinct steps. First, a polysulfone

support layer is cast onto a non-woven polyester fabric. The polysulfone layer is very porous
and is not semi-permeable; that is, it does not have the ability to separate water from dissolved
ions. In a second, separate manufacturing step, a semi-permeable membrane skin is formed on
the polysulfone substrate by interfacial polymerization of monomers containing amine, and
carboxylic acid, and chloride functional groups. This manufacturing procedure enables

independent optimization of the distinct properties of the membrane support and salt rejecting
skin. The resulting composite membrane is characterized by higher specific water flux and
lower salt passage than cellulose acetate membranes.

One advantage to use of polyamide composite membranes is that they are stable over a wider
pH range than cellulose acetate membranes. However, polyamide membranes are susceptible

to oxidative degradation by free chlorine, while cellulose acetate membranes can tolerate
limited levels of exposure to free chlorine. Also, compared to a polyamide membrane, the
surface of a cellulose acetate membrane is smooth and has little surface charge. Because of the

neutral surface and tolerance to free chlorine, cellulose acetate membranes will usually have a


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more stable performance than polyamide membranes in applications where the feed water has
a high fouling potential, such as with municipal effluent and surface water supplies.

Another advantage to use of polyamide membranes is that they have better resistance to
hydrolysis and biological attack than cellulosic membranes. They can also be operated over a
pH range of 4 to 11, but extended use at the extremes of this range can cause irreversible
membrane degradation. They can withstand higher temperatures than cellulosic membranes;
however, like cellulosic membranes, they are subject to compaction at high pressures and
temperatures. Polyamide membranes also have better salt rejection characteristics than
cellulosic membranes, as well as better rejection of water soluble organic.


Thin-Film Composites


As the name indicates, thin-film composite (TFC) membranes are made by forming a thin,
dense, solute rejecting surface film on top of a porous substructure. Because the water flux
and solute rejection characteristics of the membrane are predominantly determined by the thin
surface layer, whose thickness can range from 0.01 to 0.1 pm, the construction materials and
manufacturing processes for the layer can be varied and optimized in order to achieve the
desired combination of properties. For example, several types of materials have been
developed for the surface layer of the thin-film composite membranes, including aromatic
polyamide, alkyl-aryl poly urea/polyamide and polyfurane cyanurate. While the thin surface
layer composition often varies, the supporting porous sub layer is typically made of
polysulfone.


One disadvantage to polyamide thin-film composites is that, like polyamide asymmetric
membranes, they are highly susceptible to degradation by oxidants, such as free chlorine.
Consumers must be consistent in their maintenance of the TFC systems, particularly the
carbon pre-filtration element which is present to remove free chlorine (and other oxidative
organic) and prevent damage and premature destruction of the TFC membrane. Although
the stability of these membranes in the presence of free chlorine has been improved by
modifications of the polymer formulation and the processing technique, exposure to oxidants
still must be minimized.


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A comparison of characteristics of these three membrane types is given in Table A-1 below:


Table A-1. (Source: Aquatechnology, http: / /www.aquatechnology.net/reverse osmosis.html)

Membrane Module Configurations

The two major membrane module configurations used for reverse osmosis applications are

hollow fiber and spiral wound. Two other configurations, tubular and plate and frame, have

found good acceptance in the food and dairy industry and in some special applications, but

modules of this configuration have been less frequently used in reverse osmosis applications.


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Comparison of Reverse Osmosis Membranes

S Aromatic Thin Film
Feature Cellulosic
Polyamide Composite*

Rejection of Organics L M H
Rejection of Low
Molecular Weight M H H
Organics
Water Flux M L H

pH Tolerance 4-8 4-11 2-11

Temperature Stability Max 35 deg C. Max 35 deg C. Max 45 deg C.

Oxidant Tolerance(e.g. H L L
free Chlorine

Compaction Tendency H H L

Biodegradability H L L

Cost L M H

L = Low; M = Medium; H = High

*Thin film composite type having polyamide surface layer






Florida Department of Environmental Protection, Desalination in Florida

APPENDIX B: Thermal Distillation Processes


Thermal distillation was the earliest method used to desalinate seawater on a commercial
basis, and thermal processes have been, and continue to be, a logical regional choice for
desalination in the Middle East for several reasons. First, the seas in the region are very saline,
hot, and periodically have high concentrations of organic, which are challenging conditions
for reverse osmosis (RO) desalination technology. Second, RO plants are only now approaching
the large production capacities required in these regions. Third, dual-purpose cogeneration
facilities were constructed that integrated the thermal desalination process with available
steam from power generation, improving the overall thermodynamic efficiency by 10-15
percent (Hamed, et al., 2002; Hanafi, 2002). For these reasons, combined with the locally low
imputed cost of energy, thermal processes continue to dominate the Middle East. In other
parts of the world, where integration of power and water generation is limited and where oil
or other fossil fuels must be purchased at market prices, thermal processes are relatively
expensive (GWI, 2006a).

In the United States, thermal processes are primarily used as a reliable means to produce high-
quality product water (< 25 mg/1 total dissolved solids [TDS]) for industrial applications,
because distillation processes are very successful at separating their target- dissolved salts-
from the bulk feedwater. Distillers almost completely reject dissolved species, such as boron,
which can be problematic for RO. Distillers, however, are sensitive to volatile contaminants
that may evaporate from the feedwater and carry over into the distilled water, where they may
or may not condense.

Three major thermal processes have been commercialized: multistage flash (MSF) distillation,
multiple effect distillation (MED), and mechanical vapor compression (MVC), and each one is a
mature and robust technology (see Box B-l). MSF and MED processes demand both thermal
energy (typically steam) and electrical energy. Thermal processes are configured to use and
reuse the energy required to evaporate water, known as the latent heat of evaporation (about
2,326 kJ/kg of water or 2,438 kWh/kgal at normal atmospheric conditions). How efficiently


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the latent energy is reused is a function of project-specific economics, considering capital and
operating costs.

The combined energy requirements of thermal technologies are greater than that of membrane
processes, but it is not simple to compare the total energy use of these diverse processes,
because MSF and MED are capable of using low-grade and/or waste heat, which can
significantly improve the economics of thermal desalination (see Box B-2). Utilities in the
United States have generally overlooked opportunities to couple thermal processes with
sources of waste heat to produce desalinated water more economically.

In the Middle East, the largest of the MSF and MED plants are built along with power plants
and use the low-temperature steam exhausted from the power plant steam turbines. This
"cogeneration" approach combines water production with the generation of electric power
using the same fuel and offers a method to improve the energy efficiency of desalination
plants while sharing intake and outfall structures. Large MSF distillers are commonplace in
the Middle East largely because of cogeneration.

In another example, many of the largest modern cruise ships select the thermal MED

desalination process because MED requires 20 to 33 percent of the electrical energy of RO and
because the heat energy it requires can be obtained from the ships' propulsion engines. MSF
and, increasingly, MED units are also used in industry to make water for liquid natural gas
and methanol plants. These industrial processes have a relatively small demand for
freshwater, relative to the massive quantities of waste heat generated by the petrochemical

process, and can be designed to be quite inefficient. When the residual heat energy has little or
no value, there is no economic justification to invest in more efficient designs. Scale deposition
in thermal desalination units is a concern but is generally mitigated by control of the operating
temperatures and concentrations and use of polymer-scale inhibitors. The potential for
mineral-scale deposition in a thermal desalination plant is considered an economic
optimization issue, not a limitation of the process.

Thermal technologies, including variations of MSF's forced circulation configuration, can work
with supersaturated salt solutions and are used in brine concentrators for minimizing the


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volume of desalination concentrate. However, operating at extremely high recoveries is not
usually economical for desalination applications due to the boiling point elevation caused by
the salt. In fact, economic considerations affected by boiling point elevation normally limit
water recovery of thermal seawater desalination plant designs to about 35 to 50 percent, not
considering cooling water. Although thermal desalination technologies are mature
technologies, opportunities remain for additional cost savings. Thermal technologies are not
optimized to the highest efficiencies, due to current practical constraints in materials and
design and considerations of the source, condition, and value of the thermal energy being
utilized. All thermal processes are affected by the cost of heat transfer surfaces (which are
primarily copper or titanium alloys) and the development of new material options could

reduce these costs. Also, the methods of distributing feedwater over the heat transfer surface
of thin-film processes (e.g., MED, MED-TVC, VC) are proprietary and could benefit from
further research. There may be additional opportunities for improved efficiencies in new
designs of thermo compressors for MED-TVC systems. There are also needs for additional
research and development into improved configurations and applications to utilize low-grade
and/or waste heat and into entirely new processes that optimize the use of low-grade heat (see
Box B-2). For example, there has been a recent review of an industrial application that would
utilize low-grade energy at sulfuric acid plants (Shih and Shih, 2007). Heat is produced when
sulfur is burned and when concentrated acid is diluted. Thermal desalination plants
incorporated into this process could therefore produce the water used to dilute the acid which
in turn produces the heat required for the thermal desalination process. The location of low-
grade and/or waste heat resources near saline water sources and large consumers of water,
including industry, has not been investigated, and research on opportunities to utilize low-
grade and/or waste heat could yield economical applications of existing thermal desalination
technology in the United States.


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BOX B-1 (Excerpted from NRC, 2008)

Overview of Thermal Desalination Processes

Three primary thermal desalination processes have been commercially developed:

* Multistage flash (MSF) distillation, a forced circulation process, is by far the most robust of all
desalination technologies and is capable of very large production capacities per unit. Globally, MSF
is among the most commonly employed desalination technologies. MSF uses a series of chambers,
or stages, each with successively lower temperature and pressure, to rapidly vaporize (or "flash")
water from the bulk liquid. The vapor is then condensed by tubes of the inflowing feedwater,
thereby recovering energy from the heat of condensation (Figure 4-12). The number of stages used
in the MSF process is directly related to how efficiently the system will use and reuse the heat with
which it is provided.


HEATING FLASH AND Chemicals
I HEAT RECOVERY SECTION Added
1st STAGE 2s STAGE Nth STAGE 1t Saline
I *. Feedwater
STEAM
SEJECTOR Cooling

fr " '.-- V,]- '";,l -; S ....... JEJECTOR
Se ,,- .'- I' .;-). ... CONDENSOR
om ..'." t Contamiinated
BRINE i .. a to Waste
HEATER L., 'i. -"F s
t : Water

Condensate Discharge
Retumed ..
to Boiler

Figure 4-12. Multistage flash evaporation. SOURCE: Buros, et al. (1980); Buros (2000). Reprinted
courtesy of U.S. Agency for International Development.

* Multiple effect distillation (MED) is a thin-film evaporation approach, where the vapor produced
by one chamber (or "effect") subsequently condenses in the next chamber, which exists at a lower
temperature and pressure, providing additional heat for vaporization (Figure 4-13). MED
technology is being used with increasing frequency when thermal evaporation is preferred or
required, due to its reduced pumping requirements and thus its lower power use compared to MSF.
MED plants were initially limited in size but MED technology is planned for an 800,000 m/ day
desalination plant in Jubail, Saudi Arabia. Since the early 1990s, MED has been the process of choice
for industrial low-grade, heat-driven desalination. The largest MED plants incorporate thermal
vapor compression (TVC), where the pressure of the steam is used (in addition to the heat) to
improve the efficiency of the process.

Continued


April 2010 Page 84 of 109

















I .
S tecam i' ... its... / e for s be.n '... .. o ,e,..,,e -



to Boiler 2 0 )


Rt Brnne


Figure 4-13. Multiple effect distillation process. SOURCE: Buros et al. (1980); Buros (2000).
Reprinted courtesy of U.S. Agency for International Development.

Vapor compression (VC) is an evaporative process where vapor from the evaporator is
mechanically compressed and its heat used for subsequent evaporation of feedwater (Figure 4-14).
VC units tend to be small plants of less than 2,839 m3/day that are used where cooling water and
low cost steam are not readily available. VC systems can operate at very high salt concentrations
and the VC process is at the heart of many industrial zero liquid discharge systems (Pankratz and
Tonner, 2003).

A portion of te hot brine is
recirculated to the spray nozzls forr Il

SThe vapor gains heat energy by
mcaica being compressed by the vapor
compressor.
Seawater and SPRAY o e er ed e
Brine T VAPOR


on surplus stea is available.
1 /- ,iHEAT
EXCHANGER
I BRINE T2 1 ]

Brine Discharge o Brihe
Discharge
e uted Salater

Feedwater
t Chemicals
ldded

Figure 4-14. Vapor compression process. SOURCE: Buros et al. (1980); Buros (2000). Reprinted
courtesy of U.S. Agency for International Development.


Other non-hybrid thermal desalination approaches, including solar stills and freezing, have
been developed for desalination, although they have not been commercialized to date (Buros, 2000).
In brief, a solar still uses the sun's energy to evaporate water from a shallow basin, which then
condenses along a sloping glass roof.
condenses along a sloping glass roof.


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Florida Department of Environmental Protection, Desalination in Florida

BOX B-2 (Excerpted from NRC, 2008)

Low-Grade and Waste Heat for Desalination

Low-grade heat and waste heat are two terms that are often used synonymously but,
depending upon the application, they may have completely different meanings. The term low-
grade heat is often used to describe heat energy that is available at relatively low (near-ambient)
temperatures, which is of minimal value for industrial or commercial processes. In contrast,
waste heat, which may or may not be low-grade heat, contains energy that is released to the
environment without being used. Both have potential value for desalination.

Most of the largest desalination facilities in the world are dual-purpose facilities that
produce both freshwater and electricity. In all of these facilities at least some of the electricity is
generated by high pressure steam when it is expanded through turbines. In the case of
backpressure turbines, when the steam leaves the turbine, it can no longer produce electricity
even though it is still slightly above atmospheric pressure. The waste energy from this exhaust
steam is ideal for use by thermal desalination processes. In contrast, condensing turbines have a
cool exhaust steam under vacuum conditions. Therefore, when condensing turbines are used in
combination with thermal desalination, some low pressure steam is extracted for use in the
desalination process. Extracted low-grade steam could, in theory, be used to generate more
electricity, but practical circumstances (e.g., electricity demand, limited operating flexibility)
influence whether this low-grade energy would, in fact, be used this way. Thus, low-grade heat
might also be wasted under specific circumstances. Large slow-speed diesel generators, such as
those used to power large ships, also represent a source of low-grade heat that is often wasted.
The cooling water can easily be used to heat both MED and MSF processes without affecting the
efficiency of the power generation. Exhaust-gas boilers can also be added to capture otherwise
wasted energy for use for desalination or to generate additional electricity.

There are other potential sources for waste heat that are simpler to identify as waste, such
as industrial stack emissions or cooling circuit heat that is rejected to rivers, lakes, or the air via
heat exchangers or cooling towers. Contrary to common belief, these heat plumes may contain
useful energy, even though this energy may not be economical for use in the existing industrial
processes.

There are economic costs associated with the use of waste or low-grade heat, such as the
cost of installing and operating the heat recovery system. The act of recovering the heat may also
affect the efficiency of the main process. When a previously wasted energy stream is used, it may
then be valued as a potential revenue stream by its owner. When these costs are considered, the
energy is not free, but in many cases energy costs can be reduced to a small fraction of the total
process cost of desalination.


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