Pilot Plant Studies of Office Paper Deinking. Part 1. Process Water Recycling, 1998 Recycling Symposium Proceedings

Deinking tests were performed in a pilot plant using the sequence of unit operations: pulping, screening, thickening, kneading, and flotation. The tests were performed to study process water clarification and recycle in a mixed office paper deinking process incorporating kneading and flotation deinking. A dissolved air flotation cell and commercial water treatment polymers were used to clarify the rejects from the thickening steps (side hill screen followed by a screw press).

The same surfactant charge was added to the pulper in an original experiment using fresh water and in three process water recycles. With the proprietary deinking surfactant used, there was no evidence of increased foaming or greater flotation step yield loss in the recycle experiments. Also, there was no evidence of increased water clarification polymer dosage requirements. Brightness did not decline with an increasing number of recycles suggesting that the amount of suspended sub-visible ink particles did not increase with an increased number of recycles. There was no change in visible ink particle count or average size with an increasing number of recycles.