Maintaining the correct amount of
chlorine for effective drinking water system disinfection in a large
municipal drinking water system can be challenging. Piping system
lengths, variable flow rates and demands, and other factors contribute
to the difficulties in maintaining the optimum level of free chlorine
throughout the entire system.
One method of increasing the length of
time that the chlorine remains effective in the system is to add
ammonia. With the addition of ammonia, chloramines are formed resulting
in not only a more stable and longer lasting disinfecting residual than
free chlorine, but also the additional benefit of a reduction in the
amount of initial chlorine injection required and a similar reduction in
unpleasant chlorine odor and taste.
Although the mixing of ammonia with
chlorine to form chloramines is a safe and effective means to treat
drinking water, the addition of ammonia can create a potential hazard if
the chlorine is not present. The proper chlorine/ammonia ratio must be
maintained to form the chloramines. For this reason, system designers
are careful to select the most reliable injection system components
possible that also allow for variable flow rate requirements and permit
continuous monitoring and remote control by SCADA systems.
Chuck Boone, the Mechanical Maintenance Supervisor at the Irvine Ranch
Water District (IRWD) in Irvine, CA, became concerned about the new IRWD
reservoir management system (RMS) pilot project when the diaphragm pumps
chosen for the chlorine injection task repeatedly failed. Although
sensors in the system detected the failure and safely shut down the
system, it became obvious that a more reliable chlorine injection pump
system was required.
The cause of the diaphragm pump failures
was traced to the pumps losing prime due to vapor locking. Vapor locking
is caused by gases escaping from the fluid and building up in the pump
head preventing the valves from operating correctly. This phenomenon
commonly occurs when the pump is sitting idle, such as at night or when
the system demands are low. The IRWD maintenance mechanics worked with
the diaphragm pump manufacturers to install de-gassing valves and other
devices that would permit the pump to automatically expel the built up
gasses from the pump head, but these measures were unsuccessful. Looking
for a better way to inject chlorine, the IRWD team turned their focus to
peristaltic pump technologies.
