Pollution Prevention and Control Technologies
for Plating Operations
Section 2 - General Waste Reduction Practices
2.8 OTHER RINSING INFORMATION
This subsection contains information on methods applied for rinse
water use reduction that are not discussed in detail elsewhere
in the report.
One shop indicated that they use in-tank filtration in large rinse
tanks (PS 228) and another shop indicated that they use external
filtration for some rinses (PS 275). The filtration technology,
which is more frequently applied to process baths than to rinse
tanks, removes particulate matter from solutions. The source
of particulates for these two shops was not indicated on their
survey forms. However, it is known that suspended solids in rinses
can be caused by precipitation (e.g., mixing of alkaline cleaner
drag-out and metal-bearing drag-out) or airborne material.
Although it is not widely applied to rinsing, the use of ultrasonics
can improve its effectiveness. Ultrasonics loosen soil particles
that are not completely removed during the cleaning step. Although
one would expect the use of ultrasonics to be limited to small
rinse tanks and critical operations due to its high capital costs,
one shop reported that it uses ultrasonics in a large rinse tank
(12' x 30" x 40" deep) following electropolish (PS 022).
Another respondent suggests that ultrasonics be used in rinse
tanks whenever feasible (PS 068).
Most existing process lines suffer from a lack of rinsing. When
use of additional counterflow rinse tanks is suggested, the most
common complaint is that there is no space, thus rinsing suffers
and flow rates remain high. To gain additional tankage, some
shops partition large rinse tanks into two or more smaller sections
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