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I worked with a chromium conversion coating operation ten
years ago and we took their dilute rinse water effluent to zero, by the
following process: (1) replace each rinse tank with three such
tanks. (2) counterflow rinse water (parts go one way, rinse water the
other) from one rinse tank to another; reduce rinse water flow to 0.1 % (or
less) of the previous flow rate. (3) (optional) replace tap water for
rinses with RO water rinses -- this increases life of process tank contents
dramatically and also improves quality of coating. (4) use now more
concentrated rinse water as make up water into tank preceding the rinse -- if
you are using heated tanks, the amount of water should be approximately in
balance or can be made so.
We reduced rinse water to be treated/disposed to zero, reduced
overall process water consumption by 99.8+ percent, improved quality and
productivity (fewer rework or discarded parts due to poor quality
coating). The plant buys its RO water and has it hauled in -- less
expensive for them than operating own RO system and paying for permits, etc.,
and is effectively a no-discharge operation. Process tanks are changed out
much less frequently (water contamination dragged into tanks was the cause of
frequent changes), and the process tank contents are more readily recycled or
recovered for reuse, since they lack the water-borne contaminants.
RC
Ralph E. Cooper, Ph.D.
Attorney and Mediator San Antonio, TX 78230
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