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ION EXCHANGE APPLICATIONS IN WATER TREATMENT 12.47

ables the user to determine when resin replacement is necessary and to perform mainte-
nance and cleaning procedures before the bed deteriorates to the point where poor per-
formance occurs. It is beneficial to periodically perform complete water analyses of the
raw and treated waters and to verify that the overall water quality remains within the de-
sired limits. This is not usually practical for point-of-use systems or home systems but is
routinely done at central treatment facilities. Since ion exchange resin beds in some situ-
ations are fertile breeding grounds for bacteria, it is prudent to include occasional bacte-
rial analysis as part of the validation of system performance.

Automation
Many systems are best operated manually. Systems with only one or two vessels that re-
generate no more than once a day most likely will have more maintenance time required
to keep up with the automation than to regenerate manually. However, there are advan-
tages to having automatic regenerations. For point-of-use systems, this frees the home-
owner from a tedious chore. The automatic home system regeneration controller is usu-
ally set to regenerate on weekends or evenings when minimal water use is expected. In
large treatment facilities where multiple vessels or trains are used, automation can sig-
nificantly reduce the amount of workforce required. Automation has the advantage over
manual operation in that regenerations are performed in a predictable fashion time after
time in the same way. This reduces the possibility of human error; however, it does in-
crease the possibility of machine error. In sophisticated automated systems with program
logic control (PLC) and computer data logging, the cost of automating a system can ex-
ceed the equipment cost itself. This is an important point to consider in the planning stage
for a new ion exchange system. The more complicated control systems require more highly
skilled computer technicians to properly maintain the automatic control hardware and soft-
ware. Because the state of the art in computer automation is changing so rapidly, it is
likely that any automation system purchased today will be outdated within a few years.

Point-of-Use (Single-Home) versus Centralized Systems

Point-of-use systems have advantages for very small communities because they have lower
capital costs and because they can be applied to a smaller portion of the total water flow
and be used where consumers require or desire the removal of a specific contaminant. As
an example, a water supply that has a relatively high nitrate level, but one which is within
the USP guidelines for potable water, might be used by an adult couple without treatment
and without danger of illness. Another couple with young children might choose to treat
the water to remove the nitrates to protect the infant children against the possible illness
associated with high nitrate levels. Another example is a water supply with very hard wa-
ter. A homeowner might purchase a softener to avoid the nuisance of having hard water.
Yet another homeowner on a salt-restricted diet might prefer not to have a softener or to
limit its use to nonpotable outlets, to avoid the increase in sodium caused by the hardness
exchange. Most homeowners do not soften the water used for lawn sprinkling, which
would be wasteful but unavoidable in a central system. Individual home systems in some
cases may not have the same restrictions on waste discharge that centralized treatment fa-
cilities have. However, they have a significant drawback, in that there is seldom any pe-
riodic monitoring of the effluent quality, and the homeowner may not be aware when the
softener or purifier has malfunctioned, or that the treated water is not as purified as de-
sired. Centralized treatment systems, however, have economy of scale on their side. The
cost per unit of water produced is usually significantly less than that of the smaller sys-