and a mixing chamber located in the main water line.
Chemical injection systems also include some means of
regulating the metering pump to control the addition of a
chemical. This system should be designed to tightly
control the addition of the chemical. The control system
should ensure that a chemical is added only when water
is flowing through the pretreatment cascade and that it is
added in fixed proportion to the water flow or based on
some continuously monitored parameter, such as pH,
using an automated control system. If an automated
control system is used to inject the chemical, the
controlling parameter should be independently
monitored. There should also be a means of verifying
that the concentrations of any residuals arising from the
chemical added to the water are reduced to a safe level
before the water reaches its point of use.
When acid is added to adjust pH, a mineral acid should
be used.
6.2.6 Chemical injection systems
Systems for chemical injection should be monitored
according to the manufacturer’s instructions. If a facility
designs its own system, procedures should be developed
to ensure proper preparation of the chemical, adequate
mixing of the injected chemical with the water flowing
through the pretreatment cascade, and reduction to a safe
level of the concentration of any chemical residuals
before the point of water use. The facility should also
verify that the injected chemical does not degrade the
performance of downstream devices, including the
primary purification process. The adequacy of these
procedures must be verified using an independent
chloramines, and the use of orthophosphate or polyphosphate for
corrosion control have been associated with a decrease in the removal
of chloramines by carbon adsorption. In those situations, carbon
adsorption may need to be supplemented with other methods of
chloramine removal.
5.2.6 Chemical injection systems
Chemical injection systems may be used in the pretreatment section of
a water purification system to supplement the physical purification
processes described in the previous clauses. Applications of chemical
injection include the addition of sodium metabisulfite to remove
chloramines and the addition of acid to adjust pH.
Organic acids may act as a nutrient and allow bacteria to proliferate.
AAMI Rationale for the Development and Provision of This
Recommended Practice
A.5.2.6 Chemical injection systems
The AAMI RDD Committee expressed reservations about the addition
of chemicals to the water. However, it recognized that the addition of
chemicals may be necessary in some circumstances if a facility is to
meet the maximum contaminant levels set forth in AAMI 4.1.1. For
example, if the municipal water contains high levels of N-chloramines
or chloramine in the presence of orthophosphate or polyphosphate,
injection of sodium metabisulfite may be one of the few options
available for chloramine removal.
If chemical injection is used in the pretreatment cascade, users should
ensure that the addition of the chemical does not interfere with the
operation of subsequent purification processes, including the primary
purification process. For example, the performance of thin-film
composite reverse osmosis membranes may be affected by the pH of
the feed water. At pH levels below 7, the rejection of fluoride may be
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