PREPARED BY: SUBCOMMITTEE ON OVERSIGHT
COMMITTEE ON NATURAL RESOURCES
FLORIDA HOUSE OF REPRESENTATIVES
OCTOBER 28, 1982
Although Florida receives about 56 inches of rainfall on
a yearly average, only about two inches of that 56 inches are
available for surface and groundwater storage, since the remainder
is lost through evapotransporation or runoff. Florida's growth
rate further compounds adequate supplies of potable water, as
most of Florida's growth has been in coastal counties where a
lowering of the groundwater levels has led to an increased potential
of saltwater intrusion and a poorer water quality.
This report examines the desalination process of reverse osmosis
as an alternative to conventional methods of producing potable water
needs. Desalination of saline water is basically a process of
separation. The main types of desalting are by electrodialysis,
ion exchange, and reverse osmosis. Reverse osmosis is a mechanical
technique which in effect separates the impurities out of the water
by forcing the water through a semipermeable membrane at high pressure.
There are currently 70 desalination plants operating in Florida
utilizing reverse osmosis technology. Reverse osmosis was found
to be superior to other methods of desalination and to be generally
competitive on a cost basis with more conventional systems of water
supply. The cost effectiveness of reverse osmosis increases with
the size of the plant and the process is superior to conventional
treatment systems in removing pollutants.
It is recommended reverse osmosis be considered when selecting
a method of water supply in light of its comparable costs, superior
quality of water produced, and reduced impact to groundwater aquifers
as compared with more conventional methods of water supply.
Florida receives between 50 to 60 inches of rainfall on a
yearly average. This is more rainfall than any other state in
the continental United States except Louisiana. Why then does
an adequate supply of potable water appear to be a recurring
problem in certain locations of Florida?
First, this average rainfall data can be somewhat mis-
leading. According to the United States Geological Survey,
while the average rainfall in Florida as a whole is 56 inches
per year, this ranges from 40 inches per year in the Florida Keys
to 64 inches per year in Okaloosa County. Of this 56 inches, an
estimated 40 inches is lost to evapotranspiration and another 13
inches to runoff. Hence only about 2 inches of the original 56
inches is available for surface and groundwater storage.
Secondly, most of Florida's growth to date has been in those
coastal counties least able to provide potable water of sufficient
quantity and quality, especially Brevard, Broward, Dade, Hillsborough,
Lee and Pinellas Counties. Water quantity and quality are inter-
related in providing sufficient amounts of potable water. As
more and more water is extracted from groundwater in coastal
communities, the lowering of the groundwater levels leads to an
increased potential for salt water intrusion and eventually poorer
water quality. A number of coastal areas are currently utilizing
potable water not within the federal "Safe Water Drinking Act"
standards with respect to the amount of dissolved chlorides (i.e.
salts) in the water.
Given this disparate pattern of rainfall and growth across the
state, the choice for many coastal communities has been one of
attempting to treat relatively "abundant" sources of mineralized
groundwater in the area or relocating water of better quality from
further inland. Historically, the usual practice has been the
latter alternative based on what has been, up to now, the higher
costs of treating the poor quality water from localized sources.
However, this cost advantage may be narrowing, or, in some cases,
even nonexistent when compared with recent treatment technologies such
as reverse osmosis.
This oversight project examines the potential of reverse
osmosis as an alternative to more conventional methods of providing
potable water needs.
Desalination techniques are basically a process of separation.
The main types of desalting are by distillation, freezing, and the
use of membranes. Membrane desalting can be electrical (electro-
dialysis), chemical (ion exchange), or mechanical (reverse osmosis).
Electrodialysis and ion exchange are presently unable to commercially
produce potable water, except from low salt concentrations of
brackish water. Reverse osmosis, however, can adequately produce
potable water of a superior quality on a cost comparable to conventional
There are currently 72 operational desalination plants in Florida.
As Appendix A illustrates, most of them are located in coastal areas
of the state. Except for two plants, the 2.6 million gallons per
day flash distillation plant in Key West and the 2.1 million gallons
per day electrodialysis plant on Sanibel Island, all the other
desalination operations in the state are reverse osmosis. (Appendix B)
The flash distillation plant in the Keys, which was begun in 1967,
unfortunately has marred the reputation of desalination. Originally
designed to utilize sea water of high saline content, the change to
using brackish water of lower salt content caused unforeseen shut-
downs and malfunctions. Reverse osmosis, on the other hand, appears
to be a mechanical technology which can remove impurities and salt
concentration from brackish or sea water in a dependable fashion.
Osmosis is a natural phenomenon used by plants to move water
to the leaves by transferring it from cell to cell through the
semipermeable cell membranes. Figure 1 illustrates the principles
of osmosis when applied mechanically through reverse osmosis.
The pressurized flow through the membrane acts to separate the
"impurities" in the mineralized water from the final product of
potable water. Since 1960 significant advances have been made
in water membrane technology. In particular, fluxes (flow per
unit area of membranes) have been improved two to three fold.
Direct comparisons of water supply costs are difficult since
the final delivered costs depend upon many factors including the
plant capacity, the physical area served, and pre and post-treatment
requirements. As Appendix C illustrates, reverse osmosis is vastly
superior to other treatment methods in removing pollutants. Hence,
the cost of pre and post-treatment requirements in particular must be
considered prior to any direct comparison between reverse osmosis
and conventional water treatment methodologies.
Table 1 gives some sample cost comparisons for various types
of treatment methodologies for plants located in the Southwest
Florida Water Management District.
Delivered Price Per
Utility Type of Treatment 1000 Gallons (1977)
Lehigh Acres Conventional $1.51
Cape Coral Reverse Osmosis $1.61
Lee County Conventional $1.86
Bonita Springs Conventional $1.86
Sanibel Island Electrodialysis $2.40
The prices represent the final delivered price (i.e. what the
customers pay) and represents all costs associated for treatment
and delivery, including chemical treatment, debt retirement, energy,
legal and engineering costs as well as operation and maintenance
costs. Necessary periodic replacement of the reverse osmosis
membranes is also included as part of operation and maintenance
Table 2 is a sampling of production costs for reverse osmosis
plants throughout the country. In general, it can be seen that the
cost of production decreases as the capacity of the plant increases.
Rotunda West, FL
Ocean Reef, FL
Ft. Lupton, Colo.
Ft. Stockton, Colo.
Arkansas City, KS.
Artesia, New Mexico
Million Gallons Per Day
Water Cost Per
This relationship between plant capacity and operating cost
becomes clearer in Table 3 which gives 1982 costs data for Phase I
of the Burnt Storm South Water Retention Plant in Punta Gorda.
(See also Appendix D).
Table 3 RO Cost Data
Burnt Storm South Water Retention Plant, Phase I
Per Day Capacity Construction Costs Operation & Maintenance Costs
1 mgd $1 million $1.25 per 1,000 gallons
2 mgd $1.7 million $1.13 per 1,000 gallons
5 mgd $3.7 million $1.03 per 1,000 gallons
8 mgd $5.6 million $ .99 per 1,000 gallons
10 mgd $6.7 million $ .97 per 1,000 gallons
15 mgd $9.4 million $ .89 per 1,000 gallons
Source: Ed Clarke, Engineering
A review of Appendix B shows that most operational reverse
osmosis plants in Florida are of limited capacity. The largest
existing reverse osmosis facility in Florida began operating
this year in Sarasota. The plant produces 4.5 million gallons
per day at a production cost of $0.71 per 1,000 gallons in 1982
On July 1, 1982, the Select Committee on Water Management
attended a presentation and demonstration at this facility. The
committee was told that Sarasota had explored various alternatives
to meet their growing water demand, including surface water,
groundwater sources and the relocation of water from adjacent
Manatee County. Reverse osmosis technology was deemed to be most
cost effective as well as producing the best water quality. At a
cost of $1,750,000 for capital construction, the plant operates 225
membrane units. Each membrane unit lasts from three to five years,
and costs about $4,000 to replace. The 4.5 million gallons per day
produced by reverse osmosis is later blended and softened
with other well water to produce a maximum of 12 million gallons
per day. Waste brine from the reverse osmosis unit is discharged
into Sarasota Bay as approved by Department of Environmental Regulation
permit, where it is monitored regularly for increased total dissolved
solids, chlorides, and turbidity by the Department. (Appendix E).
99 percent of reverse osmosis water in Florida is utilized for
domestic potable water with the remainder going to industrial needs.
Reverse osmosis does have its limitations, but its ability to remove
numerous pollutants makes it superior to coagulation, chlorination
or active carbon in this consideration. More importantly, reverse
osmosis has the following additional advantages when compared with
conventional water treatment methods:
(1) Ability to meet more stringent drinking water quality
standards without incurring additional treatment to water;
(2) Ability to expand plant capacities by additional wells
into the groundwater and desalting these groundwaters, as opposed
to expanding infrastructure development of the conventional water
(3) Minimal susceptability to changing climatic conditions
and salt water intrusion.
One problem presented by reverse osmosis is the disposal of the
waste brine, especially in inland areas. However, adequate mitigation
techniques appear to be available through deep well injection in inland
areas and its return to sea water in coastal areas.
CONCLUSIONS AND RECOMMENDATIONS
The continued growth in Florida's coastal areas along with
unpredictable amounts of adequate rainfall and danger of salt water
intrusion in these areas has led to the increased use of desalination
as a basic water treatment process as well as a supplemental water
source. Of the types of desalination, reverse osmosis is clearly
the choice as the most cost-effective and dependable method. In
addition, the superior ability of reverse osmosis to remove pollutants
and the enhanced taste, smell, and drinkability of water treatment by
reverse osmosis should lend further to its increasing acceptance.
Reverse osmosis plants will probably continue to be concentrated along
coastal areas. There are, however, no major physical or economic
constraints to prevent their location inland.
It should be noted that this report has been limited to the cost
effectiveness of reverse osmosis as a source of water supply and
treatment; other issues affecting the selection of water supply
techniques such as conservation and protection of groundwater aquifers
have been ignored.
The following are suggested as areas for further study:
(1) The use of blending or combining reverse osmosis treated
water with conventionally treated potable water to produce larger
volumes of required potable water.
(2) Exploration of methods to provide incentives to those
utilizing reverse osmosis technology even where not the most cost
effective at the time. Individual incremental expansions in the
water supply capacity may not render reverse osmosis cost
effective while each additional expansion over the years would
continue to bring the unit cost down. In addition, continued
reliance on conventional water supply techniques from surface and
groundwater sources pose certain long term dangers to the water
supply which might be mitigated by the use of reverse osmosis.
(3) Counties which are considering relocating water from
other counties to meet potable water demand should compare the
cost-effectiveness of reverse osmosis treatment as one alternative.
According to the West Coast Regional Water Supply Authority,
construction costs for pipelines to transport water were
approximately $1 million per mile in 1978 dollars. This does not
include pre-treatment or production costs.
U. S. Agency for International Development, The U. S. A.
Interior Department Desalination Manual, August, 1980
Pitts, C. E. Jr., "Desalination in Florida", (unpublished
Kanel, Nagendra and Winn, Starley, "Membrane Plants in South
Florida", South Florida Water Management District, 1979.
Dykes, Glenn M., Jr. "Meeting Quality Standards in Florida"
(unpublished report by Florida Department of Environmental
Regulation) September 1979.
Oak Ridge National Laboratory, "Desalting Seawater and Brackish
Water: Cost Update." 1979.
World Water, "Desalination: Cutting energy and costs,"
U. S. Department of Interior, Water Resources Scientific Information
Center, Office of Water Research and Technology, (Phone interviews
with Department's employees), June 2-3, 1982.
STATE OF FLORIDA
* Location of Desalinization Plants
Source: -Florida Department of
REVERSE OSMOSIS, DEMINERALIZATION and DESALINIZATION
PLANTS in FLORIDA
Cove of South Beaches
Chucks Steaks House
Burnt Store Utilities
Eagle Point Nest MHP
1414 Mobile Home Park
Ocean Side Acres Apt.
Wekiva Falls Park
Greater Pine Island
Gulf Coast Resort
Imperial Harbor MH Estate
lona Trailer Ranch
Sanibel Island Water Asso.
Christian Retreat Camp
Indian River Plantation
Ocean Reef Club
Shelton Land & Cattle Co.
Pheasant Walk (Palm
Beach County System #6)
Riverside Memorial Chapel
Bay Front MHP
Bay Lakes Estates MHP
Camalot Lakes MHP
City of Venice
Fairwinds Condo. Village
Kings Gate TT Park
Lake Village MHP
Lyons Cove Condominium
Myakka River State Park
Palm & Pines MHP
Beindorf & Asso.
RO-Basic Tech .010
RO-Basic Tech .160
RO-Permutit/Low Press. .500*
RO-Applied Water .037
RO-Basic Tech .020*
RO-Basic Tech .028
RO-Basic Tech .096
RO-Basic Tech .020
RO-Basic Tech .060
RO-Basic Tech .150*
RO-Fluid Systems 1.000
RO-Gulf Roga 1.040
Basic Tech/Permutit 1.080
RO-Basic Tech/Low Press. .001
RO-Basic Tech/Low Press. .100*
RO-Purification Tech .060
RO-Gulf Environmental .006
RO-Basic Tech .001
PLANT~~ ~ ~ ~ NMSPATMN G
APPENDIX B CONTINUED
Pelican Cove S/D
Sarasota, City of
Sarasota Bay MHP
Spanish Lakes MHP
Sorrento Shores S/D
Southbay Yacht & Racquet
Workman Electronic Corp.
Bryn Maur Camp Resort
(formerly Ramada Camp Inn)
Fort Pierce Jai Alai
Harbor Br. Foundation
City of Ponce Inlet
Indian Harbor Estates
River Park MH Colony
South Water Front Park
Sugar Mill County Club
P.N. Holly Asso.
* Not yet in service.
Source: Florida Department of Environmental Regulation
THE REMOVAL OF POLLUTANTS FROM SURFACE WATER BY MEANS OF DIFFERENT TREATMENTS
Chlorination Coagulation Osmosis Carbon
Bacte ia and viruses XXX XXX XXX
Suspended matter XXX XXX XX
Total organic carbon -XX XXX XXX
Pesticides XX XXX XX
Inorganic salts -- XXX
Inorganic toxic compounds XX-XXX XXX
Ammonia (XXX) X
Phenols -X XXX
Taste and odor X XX-XXX XXX
Oil X XXX XX
Detergents X XXX XXX
Hydrocarbons X-XX XXX
Chlorinated hydrocarbons -X-XX XXX
Volatile organic acids X XX
Amino acids X XXX XX
XXX 90-100% removal
XX 50-90% removal
X 10-50% removal
< 10% removal
Source: South Florida Water Management District
REVERSE OSMOSIS COST DATA
Cost Parameter (a,b) 1.0
Capital Cost ($1000) 1,154
Electric (1000 KwHr./Yr) 2,530
Maintenance Materials ($1000/Yr.) 95
Labor (Hr/Yr) 1,949
Chemicals (Ton/Yr) 56
Total O&M ($1000/Yr) 228
Total Annual Cost ($1000/Yr)(d) 337
(/1000 gal)(d) 92
Size (MGD) (
Notes: (a) Taken From Culp/Wesner/Culp.
Water Reuse and Recycling.
OWRT/RU-79. A report to the
Office of Water Research and
Technology, U.S. Department of
the Interior. 1979.
(b) Costs are in September 1977 dollars.
Power at 4.0/KwHr. Labor at $10/Hr.
(c) For an AWT effluent.
(d) Includes capital costs ammortized at 7.0% for 20 years.
+. 7 -,4
BRIEF DESCRIPTION OF THE
CITY OF SARASOTA 12 MGD COMBINED
REVERSE OSMOSIS/ION EXCHANGE
WATER TREATMENT PLANT SCHEDULED
TO BE PLACED IN OPERATION
IN JULY 1982
CITY OF SARASOTA
12 MGD REVERSE OSMOSIS ION EXCHANGE
WATER TREATMENT PLANT
-- -- 4#
K-_ )J^ )
Sarasota's water treatment facility is capable of producing twelve million
gallons per day (MGD). Two treatment processes are utilized, each from a
separate source of supply. The products of each process are finally blended to produce
an economic, palatable and safe potable water.
DEMINERALIZATION-REVERSE OSMOSIS TREATMENT PROCESS
The supply for the Reverse Osmosis (R.O.) process is derived from six deep wells
within the City limits, specifically renovated for the purpose.
The water from these wells is relatively high in dissolved solids (1500-2000 parts
per million) which dictates that advanced demineralization be utilized.
Reverse osmosis requires considerable care in the handling of raw water from its
source to the pressure vessel, as the membranes within the vessel are delicate and
easily fouled by compounds which might be formed by chemical reaction. To preclude
the formation of such compounds, by hydrogen sulfide reacting with ferrous metal, the
R.O. supply wells are plastic lined. All R.O. raw water transmission mains are
plastic and concrete, while the pumping equipment utilizes bronze and stainless steel.
Upon entering the treatment plant, the R.O. raw water is acidified with
sulfuric acid. This serves to keep the hydrogen sulfide in solution, and improves
the efficiency of the R.O. process. Next, the feed water is filtered to remove
particulates and sodium hexametaphosphate is added. The sodium hexametaphosphate
stabilizes dissolved salts which otherwise would precipitate as a result of increased
pressure and concentration, thereby causing damage to the membranes.
The feed water is pumped into the membrane vessels at a pressure of more than 400
pounds per square inch. Pure water molecules are forced through a semi-permeable
membrane to become the product, while the dissolved salts are retained on the feed
side of the membrane and flushed from the vessel by incoming feed water. The
concentrate produced in the first stage of each rack becomes the feed to the second
stage. The concentrate remaining from the second stage flows to waste. The vessels
are arranged in three separate racks, each of which holds 75 vessels for the
two stage R.O. process. Each rack is capable of producing 1.5 MGD of finished
product; collectively, 4.5 MGD of product can be produced using all three racks at
the maximum feed of 6.0 MGD.
After leaving the pressure vessels, the product water flows to a degasifier where
hydrogen sulfide and carbon dioxide are removed. An alkaline compound is then added
to neutralize the previously induced acidity.
SOFTENING ION EXCHANGE TREATMENT PROCESS
'3 1- (
The supply for the softening process is provided by the City's Verna Well
Field, located 20 miles east of Sarasota. Water from Verna has a more acceptable
level of dissolved solids, but requires treatment to lower its hardness from 500
parts per million to 8 ppm.
Ion exchange was selected for incorporation into the new plant to produce
5.2 MGD of softened water from a flow of 5.6 MGD of raw water supplied by the Verna
Softening is accomplished by passing the raw water through vessels containing
Zeolite, a medium which exchanges the hardness ions, primarily calcium and magnesium,
with sodium ions. There are four softening units; three of which are operating
at full production, while the fourth is regenerating through the introduction of
chlorinated sea water which is the source of sodium ions.
0.7 MGD of sea water is used for regeneration, while 0.4 MGD of raw well
water is used for rinse. Both of these are wasted after use.
At Verna Wellfield, raw water is aerated and chlorinated prior to transmission
to the treatment plant. Without further treatment the quality of Verna water is
such that it allows blending of 2.3 MGD, as transmitted from the wellfield, with
9.7 MGD of demineralized/softened treatment plant product.
Blending takes place in a clearwell beneath the R.O. degasifiers, where each of
the final products flow after the respective treatment process. The blending
water is then chlorinated and transferred to storage facilities, from which high
service pumps deliver the water into the distribution system.
Thus, from 13.9 MGD of raw, mineralized well water, the needs of the City of
Sarasota are met with 12 million gallons per day of quality potable water.
- _- .
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