Production of cellulolytic enzymes by Aspergillus fumigatus ABK9 in wheat bran-rice straw mixed substrate and use of cocktail enzymes for deinking of waste office paper pulp

► Solid state mixed substrate fermentation using the ligno-cellulolytic Aspergillus fumigatus strain ABK9. ► Optimization of cellulases production through Plackett–Burman and Box–Behnken methodology. ► Enzymatic deinking of waste office paper pulp and comparison with chemical treatment. Response surface methodology was employed to optimize mixed substrate solid state fermentation for the production of cellulases and xylanase by Aspergillus fumigatus ABK9. Among 11 different parameters, fermentation time (86–88h), medium pH (6.1–6.2), substrate amount (10.0–10.5g) and substrate ratio (wheat bran:rice straw) (1.1) had significantly influences on enzyme production. Under these conditions endoglucanase, β-glucosidase, FPase (filter paper degrading activity) and xylanase activities of 826.2, 255.16, 102.5 and 1130.4U/g, respectively were obtained. The enzyme cocktail extracted (solid to water ratio of 1:10) from the ferments increased brightness of waste office paper pulp by 82.8% ISO, InkD value by 82.1%, removed chromophores (2.53 OD; A237nm) and hydrophobic compounds (1.15 OD; A465nm) and also decreased the kappa number to 13.5 from 16.8.