Page 355 - Water and wastewater engineering

8-24 WATER AND WASTEWATER ENGINEERING

This is within the typical range of 1.5 to 7.5 min.

n. Check the SFR

3
275 m /d 3 3

SFR 292 55 or 290 m /dm of water
.
094 m 3
.
3 3
This is within the typical range of 200 to 1,000 m /d · m .
o. Check the pressure drop. Using Figure 8-6 and the operating temperature of 10 C from
3 2
Example 8-2 , the pressure drop at a surface loading rate of 400 m /d · m is about 37 kPa/m
and the total pressure drop is (1.36 m)(37 kPa/m) 50.3 kPa. This is within the typical
range of 35 to 70 kPa and is less than the maximum of 140 kPa.
p. Allowing for 50% expansion of the resin bed, the tank height will be
)
.
.
.
Height of tank (1 5 )(1 36 m 2 04 or 2 1 m
.
This is less than the maximum of 3.6 m for prefabricated tanks and is acceptable.
Comment: Normally, one would not check both the EBCT and SFR as they are reciprocal of
each other. The check is performed in this example for academic demonstration and to provide
some experience with the the magnitude of the numbers and their relationship to one another.
Piping
PVC piping is most common for smaller systems. Either plastic-lined or stainless steel is used for
larger systems.

Brine Disposal
Historically, brine has been disposed to the sanitary sewer system. For small household units, the
impact on the wastewater treatment plant will not be significant. For larger municipal systems
the problem is much more significant. Those communities near the ocean have it as an option for
disposal. Deep well injection into a saline aquifer is another alternative as is evaporation. All of
these options are highly site specific.
Because the issue of brine disposal is significant, the examination of the option of ion
exchange as a treatment technology should consider the disposal alternatives and costs very early
in the design process.

8-5 OPERATION AND MAINTENANCE

The major operational requirements in addition to routine monitoring are preparation of the
regenerant and conducting the regeneration. Often these are automated.
In addition to routine maintenance of valves and pumps, periodic resin cleaning and/or
replacement will be required. Resin cleaning may require eight or more hours of out-of-service
time for the column. Extraordinary regeneration of the resin may be required after cleaning. The
cleaning agents are hazardous and may be incompatible with the column materials.
Resin life for cation resins is on the order of 10 years for softening and 3 to 5 years for anion
exchanger resins. Shorter resin life can be expected where the water fouls the resin.