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10.28 CHAPTER TEN

TO STORAGE TANK
OR DAY TANK VENT

- - PUMP HEAD
~
NOTE 2 I
NOTE 3 ~
MAXIMIZE THIS
_1
DISTANCE -'~
b
NOTE 1 ~ i
MINIMIZE THIS
DISTANCE
FIGURE 10.10 Metering pump suction piping detail. Notes: (1) Sodium
hypochlorite metering pump suction piping shall be routed to slope continuously
downward from the day/bulk storage tank. (2) Valve shall remain open except
when day/bulk storage tank level is below the pump centerline. (3) Locate tee
for vent as close as possible to pump suction connection. The vent piping shall
be connected to the run of the tee in the vertical position. Vent piping shall not
be connected to the branch of the tee.

• The piping should be sloped up toward the tanks from the pumps such that the bubbles
can flow back to the tank.
• Suction piping at the pump should be configured in a specific manner to allow for dis-
engagement of the bubbles prior to entering the pump head (see Figure 10.10).
In addition, some pump manufacturers supply a special hypo pump, which bypasses a
small amount of hypochlorite from inside the pump head to the pump discharge to allow
any accumulated air to exit the pump head. This results in a small decrease in pump
accuracy.

On-site Generation of Chlorine
Although on-site generation of disinfectants has been possible for many years, it has not
generally been found to be practical. However, new concerns over accidental release of
chlorine gas and the relatively high cost of scrubbers that may have to be installed by
many plants to prevent release of gas into adjoining neighborhoods have raised new in-
terest in on-site generation. Several systems are now available that use new technology
to generate disinfectants and use only salt and electric power. They can even be designed
to operate unattended at a remote location and are intended to meet all USEPA standards
for disinfection and maintaining a chlorine residual in the finished water.
There are two types of systems available for on-site generation. The first and most
common generates a very dilute (0.8%) sodium hypochlorite solution directly from salt-
water, and the second generates pure chlorine gas directly and sodium hydroxide as a by-
product. In the second method the chlorine can be fed in two distinct ways. Either the
generated chlorine is fed directly via a conventional chlorine feed system wherein the gen-
eration effectively replaces local chlorine storage; or the generated chlorine is remixed
with the generated sodium hydroxide to generate a concentrated (12.5 %) sodium hypochlo-
rite solution, which is stored on-site and fed with conventional metering equipment. The