25 May 2005
that is formed is allowed to settle for subsequent removal as a watery sludge. The
treated water is filtered prior to use as makeup.
Cold and Hot Processes. Adding lime and soda ash at ambient
temperature is referred to as the "cold lime-soda process." When lime and soda ash are
reacted with the water at temperatures greater than 100 oC (212 oF), the process is
called the "hot lime-soda process". The hot process removes a greater amount of the
hardness, alkalinity, and silica from the water than the cold process.
Ion Exchange Process. Several types of ion exchange units are used at
military installations. An ion exchange unit is an open or closed vessel containing an ion
exchange material, also known as resin, which has been deposited on a gravel support
bed. Most ion exchange units operate under pressure, but gravity flow units are also
available. Flow rates vary with the type of equipment but are in the range of 4 to 5.4
liters per second per square meter (6 to 8 gallons per minute per square foot of ion
exchange material surface). A backup ion exchange unit and a storage tank are
typically included to permit an uninterrupted supply of treated water. The manufacturer's
recommendations for proper equipment operation should be posted near the softening
unit. A typical ion exchange hardness softener unit is illustrated in Figure 2-2. Figure 2-3
shows a typical duplex softener.
Figure 2-2. Typical Ion Exchange Unit
Inlet Diffuser/Backwash Collector
Backwash Inlet Rinse Outlet