WSP07913

• File Number: 8277.400.200
• Description: Lower Virgin River Project
• State: NV
• Basin: Colorado Mainstem
• Date: 11/1/1986
• Title: Study of Saline Water Use at the Harry Allen Generating Station - Final Report - November 1986
• Water Supply Pro - Doc Type: Report/Study

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references. For circulating water makeup treatment, the volume of waste
produced by RO precludes Its application.

Sldestream RO treatment is an emerging application which Is being applied at
the Bayswater Station In Australia. The Bayswater Station Is presently In
startup. Based on operating experiences on power plant wastewaters, the
sldestream application of RO should be technically viable, but has not yet
been commercially demonstrated.

The use of spiral wound RO as a wastewater concentration process has been
demonstrated at the R.D. Nixon Station In Colorado, the San Juan Station In
New Mexico, and the Martin Lake and Monticello Stations In Texas. The com-
bined experiences of these power plants have shown that RO Is a commercially
viable wastewater treatment process, provided proper design, operating and
maintenance approaches are appl led. Application of spiral wound RO to was-
tewater concentration was not considered economically feasible because of the
pretreatment and disposal costs associated with the Lower Virgin River Unit
water quality.

Seeded RO, using a calcium sulfate seed slurry process to prevent scaling, Is
an emerging technology with potential makeup water and wastewater applica-
tions. Seeded RO requires minimal pretreatment compared to conventional RO In
applications where calcium and silica reductions are required In the feed
water. Seeded RO has been demonstrated through laboratory tests In the U.S.,
a pilot test at the Hunter Generating Station In Utah and through pilot tests
conducted In South Africa on mine wastewaters.

The laboratory and pilot tests showed that the seeded RO process Is techni-
cally viable, but that membrane life Is sensitive to specific wastewater
quality. Seeded RO was not selected for application In the water treatment
process designs because It has not been demonstrated on a commercial scale and
accurate capital and operating cost data Is not yet available.

Although reverse osmosis Is a commercially viable and economic process for the
production of high quality boiler makeup water, the chemistries of the Lower
Virgin unit and secondary sewage effluent In conjunction with the water
quality requirements of the generating plant make It uneconomical for these
applications. Reverse osmosis (as a waste treatment option) was therefore
rejected from further consideration.

Electrodialysis

Electrodialysis (ED) is similar to reverse osmosis In that semipermeable
membranes are used for removal of dissolved sol ids. The primary differences
I Ie In the characteristics of the membranes and the driving force. An ED sys-
tem contains a stack of alternately placed cation and anion permeable
membranes with spacers which allow flow paral lei to the membranes. A DC cur-
rent provides the motive force for the selective Ion migration through these
membranes. Modifications to the basic ED process Include Electrodialysis
Reversal (EDR) where the polarity of the DC current Is periodically reversed
automatically which provides for on-stream cleaning of the system and a reduc-
t i on I,n the fou I I ng potent I a I and lower c hem I ca I requ I rements.

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