WSP10809

• File Number: 8273.500
• Description: Colorado River Basin Salinity Control - Federal Agency Reports - EPA
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 4/1/1978
• Title: Integrating Desalination and Agricultural Salinity Control Alternatives
• Water Supply Pro - Doc Type: Report/Study

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hardness), comparatively cold
range of 10,000-50,000 mg/~.
the range of 5-50 mg/~.

in temperature, and having a TDS
Product water will be normally in

The variety of waters that might be desalted by any system
includes sea water, brackish and saline groundwater, and brackish
surface waters including irrigation return flows. Many of these
waters contain substances deleterious to desalting plant oper-
ation. Dissolved gases and organic materials are usually con-
trolled by deaeration and ultrafiltration. However, one of the
principle problems in desalination systems is the potential for
scaling due to high concentrations of calcium. As a general rule,
waters having calcium concentrations above 600 mg/~ should be
pretreated (such as the injection of a polyphosphate). In this
study, it is assumed that sodium hexametaphosphate is utilized
in all cases and that by so doing, the allowable calcium con-
centration in the feedwater in 900 mg/L The total dissolved
splids concentration is also limited to 60,000 mg/~. Thus, the
ratio of brine to product is defined as (U. S. Department of the
Interior, 1973):

[1-50/TDSi
BPR = max or
900 -1
Ca.
~

TDS. - 50 J

60'~00-TDSi

. . . . . . . . . . . . . . . . . . (47)

in which,
BPR =
TDS. =
~
Ca. =
~

brine to product ratio;
TDS in feedwater, mg/~l and
calcium concentration in feedwater, mg/~.

The volume of brine may therefore be written:

Cb = Cp x BPR .........................................(48)

Multi-stage flash distillation processes, as well as other
distillation processes, require cooling of product (and possibly
brine) discharges. This may be accomplished by direct exchange
with cooling water or through the use ofa cooling tower. The
volume of cooling water (C , m3/day) is determined from;
w

Cw
Cw

= C (4.2
P
= Cp (2.5

system intake (C., m3/day) can be written:
~

- BPR),
- BPR),

(cooling tower) .................. (49)
(no cooling tower) ............... (50)

The total

Ci = Cp
c. = c
~ p

(1.2 + BPR), (cooling towers) .................(51)
+ Cb + Cw, (no cooling towers) ................ (52)

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