AbstractThe effect of fungal pretreatment of Hornbeam (Carpinus betulus) wood chips on the performance of treated pulps was studied. The chips were pretreated with P. chrysosporium BKM-1767 fungus at 1, 2, and 4 weeks using an inoculation temperature and relative humidity of 39 oC and 65%, respectively with two pulping times (80 and 90 min) and three sodium sulfite charges (14, 18, and 22%). The cooking temperature of 165 °C, and liquor-to-wood ratio of 7:1 were kept constant. Beating energy consumption showed a maximum savings of 43% for four-week treatment of wood chips with the fungus. The screen yield of the unbleached CMP ranged between 76 and 84% depending on the chip inoculation time and cooking conditions. A decreasing trend in screen yield of the pulp after chips incubation could be explained by the enzyme action on the lignin or polysaccharides. Pulp strengths including tensile, burst, tear, and fold declined with an increase in chip treatment time. Applying 3% H2O2, 4.2% NaOH, 3% NaSiO3, and 0.3% DTPA for 1 hour in two similar stages and 2 weeks fungal pretreatment of chips showed the best optical properties of bleached pulp. After a two-stage H2O2-bleaching sequence, the maximal brightness value for the control and biopulps were 54.8% and 56.2%, respectively. Overall, two-week treatment showed the better performance of P. chrysosporium on Hornbeam chips.