5368

                                                             001 R77106

                     Desalination of Brackish Groundwater
                            by Claire M.  Gesalman


           Reports of groundwater quality and availability show that in
      some areas high concentrations of  dissolved solids  are  the norm
      (2,3,6,9).  For example, in eastern Colorado much of the land is
      underlain by aquifers containing water with 3,000-10,000 mg/1
      total dissolved solids (TDS).   Aquifers containing  water with
      1,000-3,000 mg/1 TDS  are prevalent  in much  of the rest  of the
      state (9).  In several subregions  of Wyoming, the dissolved solids
      concentration in groundwater ranges from 200-9,000  mg/1 (9).
      Other western states  including New Mexico,  Montana, Arizona,  and
      Utah have areas of poor groundwater quality because of  dissolved
      solids levels (9 ) .

           A 1979 U.S. Department of Interior report cited an earlier
      report by the American Water Works  Association (AWWA)  stating that
      more than 3,000,000 persons in the  U.S. were served by  systems
      supplying water with  more than 1,000 mg/1 of dissolved  solids (3).
      Some of the sources contained over 3,000 mg/1 TDS.   Those persons
      were served by 1,066  utilities with raw water containing 1000-3000
      mg/1 TDS and 31 utilities with 3,000-10,000 mg/1 TDS in their feed
      water.  Only a few of these were being treated.   According to a
      1977 article in Desalination (5) which reported a 1973  AWWA study,
      10% of the finished water supplies  in the U.S. contained more than
      500 mg/1 TDS, and high TDS groundwater supplies are prevalent in
      the Northern Great Plains, the Southwest, Illinois, and Florida.

           The areal extent of aquifers  containing high TDS  levels (8),
      population served by  wells producing poor quality water, and
      present growth in arid areas suggest that increased use of water
      with high TDS may be  required.  It  is necessary to  ask  whether
      this water can be treated to yield  water of acceptable  quality
      at a reasonable cost.

           Research in treatment technology has produced  major advances
      in the past few years,  particularly in membrane technology (6).
      For example, low operational pressure membranes are being tested,
      offering savings in energy use, capital cost, and maintenance
      costs .

           The first commercial electrodialysis (ED) plant was installed
      in 1915.  Improvements such as development  of synthetic membranes
      have resulted in large scale application of electrodialysis for
      reducing dissolved solids in water.  The 40 ED plants  in the U.S.
      produce 7 million gallons per day  of potable water.  (World-wide,
      800 ED plants produce 60 MGD of treated water) (2).  Source water
      for ED plants usually has 1000-10,000 mg/1  TDS.
 23r> -  •••           -••JS,..;-  . '        - 1 -

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     Reverse osmosis has been the subject of significant develop-
mental work since 1953 (2).  Most reverse osmosis (RO) plants
operate with raw water sources containing 1000-45,000 mg/1 TDS.
As of January 1977 there were 518 RO plants with a total capacity
of 167 MGD (4).  Of those, 290 were in the U.S. (3).

     Feasibility and cost projections were reported in 1977 for
15 communities served by high TDS groundwater  (941-3236 mg/1) (6).
The communities studied were located in Colorado,  New Mexico,
Texas, Arizona, Iowa, North Dakota, Montana, South Dakota, Kansas,
and Hawaii and had populations ranging from 720 to 59,000.  The
treatment cost projections ranged from $0.37/1000 gallons to
$1.57/1000 gallons.  Technological improvements have led to lower
costs than were projected in an earlier study based on 1970-73
technology ($0.42-$2.09/1000 gallons, in 1977 dollars).  These
technological  improvements outweighed increased energy and other
costs.  The report concludes that in spite of higher costs, the
ratio of benefits to costs is probably more favorable now for
many communities that lack suitable low TDS water supplies.

     The most  recent inventory of desalting plants was completed
by the Office of Water Research and Technology (U.S. Dept. of
Interior) in 1977.  Of the 481 desalting plants with capacity
of at least 25,000 gallons per day listed in the U.S., 66 were
for municipal water supplies (4).  Listed plants were located
in 15 states.

     A three-volume report on commercial membrane desalination
plants was published in 1980 by the Office of Water Research
and Technology (2). It included detailed information about 24
desalination plants currently operating in the U.S. and in Carib-
bean nations.  Ten of the plants have water sources containing
more than 3,000 mg/1 TDS.  Seven of the ten are groundwater
sources, four  of which range fom 7,000-10,976 mg/1 TDS.

     o    In Rotonda West, Florida, a 500,000 gallon/day (GPD)
reverse osmosis plant has been in operation since 1973.  It treats
well water containing more than 6000 mg/1 TDS at a cost of
$1.88/1000 gallons.

     o    A one million gallon per day (MGD) reverse osmosis plant
has been operating since June 1976 in Rock Harbor, Florida.  The
source water from the Floridan aquifer varies from 5000-9000 mg/1
TDS.  Treatment cost is $1.35/1000 gallons.

     o    The  reverse osmosis plant in Ocean Reef, Florida treats
930,000 GPD at a cost of $1.26/1000 gallons.  The original plant
was installed  in 1972, with additional capacity installed in 1973
and 1974.  The feed water from five wells contains 5000-8000 mg/1
TDS.
                              - 2 -

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     o    A 300,000 GPD reverse osmosis plant was installed in
1974 in Card Sound, Florida.  It treats water from five wells
containing 5000-8000 mg/1 TDS at a cost of $0.89/1000 gallons.

     o    Lake Killarney in the Bahamas is the source of
9000-18,000 mg/1 TDS water that is treated in a reverse osmosis
plant.  This plant, in operation since March 1977, produces
600,000 GPD of treated water at a cost estimated at $2.75/1000
gallons.

     Table 1 shows size, operating cost, and other data for those
plants and others treating less highly mineralized water.

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                       References
Adams, H.J. and W.H. Brant.  1977.  The reverse osmosis
water-treatment plant at Minitonas, Manitoba.  Jour.  AWWA
69:352-355.

Data collection and analysis of commercial membrane
desalination plants.  1980.  DSS Engineers,  Inc.  for Office
of Water Research & Technology (U.S. Dept. of Interior),
Contract # 14-34-0001-8531.  Vol. I (PB81-170573 );
Vol II (PB81-170581); Vol. Ill (PB81-170599).

Desalting handbook for planners.  1979.  Office of  Water
Research & Technology (U.S. Dept. of Interior).
OWRT TT/80 3.

Desalting plants inventory report no.  6.  1977.  Office of
Water Research and Technology (U.S. Dept. of  Interior).

Hughes, M.V., Jr. 1977.  Water requirements  and desalting in
the United States of America.  Desalination  21:301-307.

Mattson, Melvin E. and Melvin Lew.  1981.  Future trends
in membrane desalination,  presented at Ninth Annual Conf.,
Natl. Water Supply Improvement Assoc., Washington,  D.C.,
May 31-June 4, 1981.

Miller, E.F. 1977.  Demineralization of brackish  municipal
water supplies - comparative costs.  Jour. AWWA 69: 348-351.

The National Atlas of the United States of America.  1970.
U.S. Geological Survey (U.S. Dept. of Interior).

Westwide study report on critical water problems  facing the
eleven western states.  1975.  Bureau of Reclamation (U.S.
Dept. of Interior).
                         - 5 -

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