Bleaching sequence (PF) for deinked pulp, (woodfree type) and its impact on the environment

The bleaching sequence P (H2O2) (Pulper) F (FAS)(tower) for sorted Mixed Office Waste (MOW) containing approximatively 3-4% (W)/(W) mechanical pulp gave a higher and more stable brightness than a single stage (F-tower). The brightness gain associated with the P-pulper, with an addition rate of 0.9% (W)/(W) H2O2 seems to be approximately 3.3% ISO. Using the PF bleaching sequence under the present mill's conditions does not allow us to use an unsorted Office Mix and to meet the +78% ISO brightness targeted In fact, this objective can only be obtained by using a sorted Office Mix. When hydrogen peroxide was added into the pulper and/or the pH of the untreated deinking plant effluent (clarified water) increased, the following changes on the characteristics of the deinking plant effluent were observed: i) higher concentration of suspended and dissolved solids; ii) higher concentration of sodium, resin acids, dioxines, furanes and toxicity; iii) lower concentration of calcium, magnesium and color. From indirect observations, it can be inferred that AOX affinity for fibers is greater when the hydrogen peroxide stage is added and/or the untreated effluent pH is higher. From indirect observations, it can be inferred that AOX affinity for fibers is greater when the hydrogen peroxide stage is added and/or the untreated effluent pH is higher.