Bearing Wastewater Treatment
Copper can be found in many wastewater sources including, printed
circuit board manufacturing, electronics plating, plating, wire
drawing, copper polishing, paint manufacturing, wood preservatives
and printing operations. Typical concentrations vary from several
thousand ppm from plating bath waste to less than 1 ppm from copper
cleaning operations. Copper can be removed from wastewater by
precipitation as an insoluble hydroxide salt or by ion exchange.
Hydro-Flo Technologies designs and manufactures many types of metal precipitation
systems including small and large
batch type and a range of
continuous flow treatment systems.
Precipitation of the insoluble cupric hydroxide salt is the most
common form of treatment. This salt is formed by adjusting the pH of
the water to about 9 to form the precipitate. The resulting
precipitate can leave about 0.1 ppm of dissolved copper in solution
if chelates are absent. If chelates are present, the final copper
concentration can be much higher. When chelating agents are present,
Hydro-Flo can design a treatment system using special metal trapping chemistry.
Ion exchange can be used to remove copper from wastewater.
Hydro-Flo ion exchange systems are designed to
treat plating rinse water with trace amounts of metals. The water is
sent through cation and anion resin beds, along with activated
carbon and/or media filtration to produce deionized water that can
be returned to the process. The advantage offered by Hydro-Flo ion exchange
systems is that the resin is regenerated on-site, eliminating the
need for bottle haul off. Since the regenerate waste will contain
any copper and other metals removed during treatment, a vacuum
distillation system can be used to concentrate the regenerate even
further to reduce the amount of liquid waste hauled away. The
purified water from the vacuum distillation system can also be
returned to the process.
The equipment normally used for these processes is a batch
treatment system for high copper concentrations (greater than 1000
ppm), continuous precipitation if the copper concentrations are less
than 1000 ppm and the volume is greater than 5000 gpd. Ion exchange
is feasible if concentrations are less than 20 ppm and the desired
effluent requires low copper concentrations, less than 20 ppb.
The typical method to remove copper
from wastewater is as follows:
Stage 1 Precipitation:
pH is adjusted upward to a pH of 8-9.5 to the optimum chrome
hydroxide precipitation point. Often, a coagulant such as ferric
sulfate is added to enhance metal co-precipitation and the formation
of “pin floc”.
Stage 2 Flash mix:
The wastewater with it’s precipitated pin
floc is introduced to the flash mix zone where a polymer flocculent
is added. This stage maximizes flocculent dispersion throughout the
Stage 3 Flocculation:
The wastewater is now introduced to the slow mix zone to agglomerate
the pin floc into larger rapid settling particles.
Clarifier, Inclined Plate:
The flocculated wastewater is introduced into the clarifier where
the settling particles accumulate in the sludge chamber. The
clarified water then exits the clarifier and flows downstream to
sewer or further treatment if necessary.
Clarifier Sludge Handling:
The accumulated sludge is periodically removed from the clarifier
and sent to a sludge holding tank where it further thickens for
disposal or dewatering.
Sludge dewatering is typically handled by a Filter Press. After
processing a batch of "sludge" the filter press is emptied of
“chrome cake” which is a semi solid of approximately 20-35 %
solids. Chrome cake is high in chrome and sulfite and should be
disposed of according to environmental regulations.
Plating shops are found in typically two
categories, captive and independent shops. Some industries operate
their own captive, in house plating operation while others outsource
to an independent plating operation.
Typical industries include: