MIL-HDBK-1165
water. The water flows in the opposite direction and exits out
the first and dirtiest rinse tank.
5.3.2.4
Water Recycling, Reclamation, and Reuse. The
procedures and retrofits described above will significantly
reduce the amount of water used in rinsing processes. To avoid
wastewater discharge altogether (zero discharge), or to at least
minimize it, the implementation of a recycling or reclamation
system is recommended.
a) Recycling. One type of recycling system that
recycles the rinse-water one or more times then discharges it is
called "reactive rinsing". It is less expensive than
countercurrent rinsing since it does not require extra tanks.
Reactive rinsing can be implemented in one of two ways; (1)
intraprocess or (2) interprocess.
b) Intraprocess. Intraprocess reactive rinsing can be
used for a single plating process that employs several different
baths and several rinse tanks to rinse away each solution.
Instead of using fresh water for each rinse tank, the discharge
from one tank is used as the rinse-water in another tank, if
appropriate (meaning the chemicals will not harm the second tank
rinse). Thus, the water is reused in the plating process before
being discharged.
c) Interprocess. Interprocess reactive rinsing can be
used when there are more than one plating processes operating
simultaneously. Instead of requiring a separate freshwater feed
line for every rinse tank, rinse-waters from rinse tanks in one
process are reused in the rinse tanks of another process.
d) Reclamation. Reclamation of used rinse-water or
plate bath solutions for use in the same processes requires a
more costly and complex approach. There are several separation
technologies available that are designed to recover plating
metals, acids and other chemicals from the water, but not
specifically to conserve the water. If beneficial use of the
water itself is the focus, any treatment technique must be
capable of producing reclaimed water that is suitable for use in
either the rinse tank or plate bath. The major separation
technologies include: ion exchange, reverse osmosis,
evaporation, and diffusion dialysis or electrodialysis.
Filtration should be used as a pretreatment for these methods to
first remove undissolved, suspended impurities in the water. A
description of each is provided here.
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