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Water Based Flexographic Ink Wastewater Treatment
System
Process Description
Water based flexographic ink is generated in
facilities that make ink or make the paper goods that the ink is
used on such as printed craft paper, boxes, cartons, paper bags,
news print, tabloid print, contract printers, wrapping paper, and
some consumer packaging.
Flexo ink wastewater is generated when the ink
delivery and storage systems are cleaned, when inks are changed
over, and for cleaning the ink shipping containers. The wastewater
contains ink solids and color and must be reduced prior to discharge
to sewer. If color persists, an oxidizing step such as chlorination
may be necessary. Check with local discharge authorities
Treatment of the flexographic wastewater is
done by first lowering the pH to ~ 2-3 pH using acid to break the
emulsion. The wastewater is then pH adjusted upward to ~8 using
caustic to begin the precipitation process. Some difficult ink
wastewaters may require coagulants. The ink and other solids in the
wastewater will coagulate. A flocculent is then used to agglomerate
the solids and provide a rapid settling particle.
The typical
method to water based flexographic inc wastewater is as follows:
Stage 1 Emulsion Breaking/pH adjustment:
pH is lowered to ~2.5 with acid using the pH controller.
Acidification is done to break the ink emulsions.
Stage 2 Precipitation and Coagulation/pH adjustment:
pH is raised from ~2.5 to 8.5 with the pH controller using caustic
while adding a coagulant if needed such as iron or aluminum salts.
Testing of the wastewater may confirm that a coagulant is or is not
needed. A “pin floc” is developed in this chamber indicating the
precipitation is complete.
Stage 3 - 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 coagulated
wastewater.
Stage 4 - 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 land on the inclined plates and are directed
downward and into the sludge chamber. The clarified treated water
then exits the top of the clarifier and flows downstream to sewer or
further treatment if necessary.
Clarifier Sludge Handling:
The resulting clarifier waste sludge is periodically removed from
the clarifier at a slow rate and sent to the sludge holding tank
where it further thickens and accumulates a batch for disposal or
processing in a filter press.
Sludge Dewatering:
The thickened clarifier sludge is allowed to accumulate sufficiently
to provide a full batch for the Filter Press. The filter press is
first prepared with a precoat of DE slurry used to coat the press
with a fine particle filter and prevent blinding of the cloths.
Once the filter press is pre-coated, the sludge is pumped until the
filter press is full. The filter press is then emptied of the
“cake” which is a semi solid of approximately 20-30 % solids.
Sludge cake is high in ink solids and should be disposed of
according to environmental regulations.
APPLICATIONS:
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