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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.


  • Printing companies.

  • Cardboard box and carton makers.

  • Newspapers and periodicals printers

  • Paper bag makers

  • Wrapping paper makers.