The Impact of Water Clarification on Deinking Systems

The water intensive nature of paper mill operations demands close attention to the recovery and re-use of process waters in all stages of the paper-making system. It is doubly important in de-inking operations because of the quantity of ink and other contaminants concentrated in the filtrates and other potential discharge streams. The value of water clarification and recycling is much more than simply the reduction of water usage and effluent discharge. because the benefits of fibre recovery, heat conservation and improved system stability make a significant contribution to the overall mill efficiency. Secondary fibre systems, and de-inking operations in particular, have the added complication of containing components such as coating, fillers and sizing that must be removed to produce quality fibre. The removal is achieved most readily through the water flow in the system. The degree of water treatment required depends on the waste paper grades used and the paper grades to be produced. Flow sheets and data from existing installations using Dissolved Air Flotation Clarifiers in tissue, newsprint and fine paper mills are presented and discussed in the following.