Reverse Osmosis and Other Treatment Technologies - Global Drinking Water Management and Conservation - page 57

polysulfone hollow fiber membranes, which are placed asymmetrically with the

feed stream. The advantage of the polysulfone membrane is that it is chlorine
tolerant. Therefore, as biological growths build up on the membrane, a backwash of
water combined with chlorine can quickly sterilize the membrane. In addition, the
ultra-

ltration membrane has a barrier surface that is capable of removing water-
borne pathogens, such as Cryptosporidium, Giardia, and other viruses.
Since the ultra- ltration pretreatment technology can be easily cleaned and

prevents waterborne pathogens, the water pressure necessary to force the water
through the RO membrane can be substantially reduced. In many cases energy
requirements will be as little as 4.69 kWh/m 3 of water to operate depending on the
amount of contaminants in the water (Dore 2005 ). In 2006, the energy needs for RO
had fallen to 2.33 kWh/m 3 , according to Gilau and Small ( 2006 ).

4.3.1.1 Recent Experience with New Desalination Projects in the USA

Two recent examples of RO desalination plants are instructive. First, the desali-
nation plant in Tampa, Florida, is the largest operating seawater facility in North
America at 25 MGD, or 94, 635 m 3 /day. In the initial planning in the late-1990s this
plant was expected to be a cost-effective supply option. However, the Tampa plant,
a facility to desalinate heavily brackish estuarine water, encountered technical and
economic problems. For example, less freshwater was produced than anticipated;
the RO membranes were subject to fouling, and

financing issues during construc-
tion and startup raised the cost of the freshwater produced. The Tampa project
illustrates some of the risks of working with private sector water developers,
without an adequate external review and the establishment of sound accountability
mechanisms (Carter 2013 ).
Second, in 1998, north of San Diego in Carlsbad, California, a private joint
venture, Poseidon, initiated its effort to build a 50 MGD (189,271 m 3 per day)
seawater desalination facility to sell water to San Diego ' s water system. In

November 2009, project received the necessary permit. In

November 2012, the San Diego County Water Authority approved the purchase of
the desalinated water for 30 years. In 2012, the project costs were estimated at close
to $1 billion, which represents a signi

“ Poseidon Carlsbad ”

cant increase from estimates a decade earlier
at $270 million; the cost for delivered desalinated water from the plant is estimated
at $1,600 per acre-foot, or $1.41 per cubic meter. The plant is expected to complete
construction and begin water deliveries in 2016. The participation of the private
sector necessitated lengthy negotiations, which took time. While Poseidon owned a
prime location site for a desalination facility, the water authority and public were
hesitant about the arrangement because of concern over pro t-taking by a private

entity engaged in the provision of a public service. After more than a decade, this
and other concerns (e.g. environmental impacts) were overcome. The Poseidon
Carlsbad experience has yielded lessons about the public s expectations for trans-

parency and protections when the private sector is involved in desalination or other
aspects of public services and infrastructure (Carter 2013 ).

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