Standard alkaline flotation deinking and neutral enzyme-aided flotation deinking were compared at pilot scale using a typical woodfree paper composition (30% coated sheet fed offset printing, 35% HP laser printing, and 35% OCE copy). Speck contamination of the pulps was 88 % lower after the enzyme treatment than the alkaline treatment. Based on this result, full-scale en/ymatic deinking experiment was carried out at Moulin Vieux mill, Pontcharra, France. The mill produces woodfree deinked pulp from 100% printed coated woodfree papers. Efficiency of the enzymatic deinking was compared to that of the standard deinking. 4 - 6 additional brightness points were obtained with the enzymatic deinking compared to the mill chemistry deinking. Residual ink content in the enzyme treated deinked pulp was lower. The mechanical properties were maintained and enzymes did not cause runnability problems on the paper machine. However, COD load was observed to be 20 - 40% higher than in the standard process. For woodcontaining recovered paper, the results obtained at pilot scale showed that good ink removal and a lower speck contamination were obtained by enzymatic treatment in neutral conditions but, in spite of a reduced amount of ink, brightness was lower. The lower brightness was recovered by a post-bleaching stage.
展开▼
