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The most universally used solution in the metal finishing
industry today is water. Any water used in a metal finishing
processing line, must be properly treated prior to being
discharged from the facility. The treatment of these
waters can be as simple as pH adjustment, oil / grease
removal, cyanide destruction, metal removal, and any
combination of the above.
The treatment of rinse waters, or spent process baths
can be done in many ways depending on what is being
removed. Continuous flow thru or batch treatment systems
are available.
The cleanliness of the water being discharged is regulated
on the Federal, State, and local level. The regulations
depend on where the water is being discharged to. Direct
discharge into streams or lakes has different regulations
than discharging into a Publicly Owned Treatment Works
(POTWs). Consult your local regulatory agencies for
discharge requirements in your area.
Some facilities have chosen not to discharge any waters
from their metal finishing operations. This eliminates
having to comply with any discharge regulations, but,
does require special treatment equipment, and periodic
shipments of concentrated material to a disposal facility.
Discharge regulations depend on the classification
of your facility and whether you are an “existing”
generator or are a new generator. They further differ
if you are an electroplating job shop facility or a
machine shop, as noted in Tables 1 & 2.
As mentioned above, any solutions used in a metal finishing
operation, must be treated to remove the undesirable
or pollutant material. When rinse waters are treated
or processed through pollution control equipment, a
waste material is generated. This waste material can
be hazardous or non-hazardous depending on it’s
contents. This material can be of many different forms
depending on the treatment technology used.
For many years, conventional precipitation systems have
been used to produce insoluble metallic hydroxides,
then filter these out with clarifiers and filter presses.
See our section on FILTER PRESSES for more information.
Recent developments in membrane technology has improved
on this concept, reducing the size of the system while
improving the end result.
Ion exchange systems help to remove anions and / or
cations present at very low levels. These systems use
resin beds which attract the unwanted material. When
the resins become saturated, they can be regenerated
and used over. The resultant waste is a concentrated
material which must be disposed of.
Electrolytic plate-out systems can also remove unwanted
cations or metallics down to very low levels. The resultant
waste is a plated cathode panel which may be sold to
a scrap house.
Some facilities have chosen not to discharge any waters
from their plant. This eliminates the need for discharge
permitting. These facilities collect their rinse waters
in a holding tank, remove as much water from these solutions
as possible, then have the concentrated material hauled
away for disposal. This helps reduce the disposal cost.
Diffusion dialysis technology is also available for
the removal of contaminants from acidic solutions in
order to extend the life. Anodizing baths, sulfuric
acid, and nitric acids can be purified by using diffusion
dialysis.
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