Fluoridation - Operation
Monitoring
Since excess fluoride
concentrations in water can cause
illness, the operator should monitor the fluoride concentration
at least once
per day to prevent overfeeding. Underfeeding is less of a problem
than overfeeding and fluoridation
equipment can be shut down for cleaning and maintenance for short time
periods without shutting down the entire water treatment plant.
In addition to monitoring the fluoride concentration manually, a type
of flow meter called a pacing meter
can be be used to match the feed rate of fluoride to the flow rate of
the water being treated. Pacing meters measure the total water
flow rate and then produce a signal which allows for automatic
adjustment of the fluoride feed rate. This type of meter is only
required in systems in which the flow rate is very variable. Even
in systems containing pacing meters, the fluoride concentration in the
water should be tested daily by the operator.
A second type of flow meter is also used in fluoride systems.
This is a simpler water meter used to merely measure the flow rate
of water within the plant. This type of meter is not connected to
the chemical feeder and is used by the operator to determine
what flow rates the feeder must accommodate.
Troubleshooting
If daily monitoring shows a change in the fluoride concentration of
treated water, the operator will need to be able to determine and
correct the problem. A variety of factors can influence fluoride
concentrations, and some of the most frequent problems will be
discussed below.
The most common cause of low or erratic fluoride concentration is
improper equipment maintenance or operation. The following
factors may cause low fluoride readings in treated water:
- Undersized solution tanks, detention time of less than five
minutes, inadequate solution water, and inadequate mixing in dry
feeders.
- Inadequate chemical depth in saturators.
- Fluoride feed ahead of the filters.
- Unfluoridated water mixing with treated water in the
distribution
system.
- Low chemical purity.
In contrast, high fluoride readings are often the result of
improper testing procedures. If the high fluoride readings are
accurate, they may result from not taking the initial fluoride content
of the water into account when calculating optimal fluoride dosage.
The water quality can also influence fluoridation to some extent.
When water with a hardness greater than 10 ppm is fluoridated using a
saturator, scaling can form on the saturator walls. The scaling
consists of
low solubility calcium and magnesium fluoride compounds. Scaling
can be prevented by water softening upstream.
Safety
Although fluoride is safe to drink at the concentration recommended for
treating
public water, the chemicals used to treat the water are handled by the
operator in much higher concentrations. Rubber gloves, coveralls,
and protective eyewear should be worn when handling fluoride.
Solid forms of fluoride are the most problematic to operators,
since inhaling
fluoride dust is very dangerous. A dust collector should be used
and a respirator should be worn when handling fluoride powders.
Liquid forms, such as
hydrofluosilicic
acid,
can also be dangerous. Hydrofluosilicic acid produces poisonous
fumes which must be vented and which are irritating to the skin.
The liquid itself can cause burns when allowed to touch skin.
The most extreme safety
problem when dealing with fluoride is fluoride poisoning, which can be
fatal. However, fluoride poisoning occurs only when a large
amount of fluoride - approximately one tablespoon - is ingested.
This
is an amount much larger than would normally be inhaled while handling
dry fluorides. Accidental ingestion of fluoride chemicals can
occur through contaminated food and drink. The operator should
always wash his hands after handling fluoride chemicals and should not
eat, drink, or smoke in areas where fluorides are used or stored.