Production of thermo-alkali-stable laccase and xylanase by co-culturing of Bacillus sp. and B. halodurans for biobleaching of kraft pulp and deinking of waste paper.

Abstract

To reduce pollution and cost of treatment for fresh and recycled paper, co-production of xylanase and laccase was carried out in the same production medium using two compatible species of Bacillus. These co-produced enzymes were used for deinking of old newsprint (ONP) and biobleaching of eucalyptusKraft pulp. Solid-state co-cultivation of Bacillus sp. and B. halodurans FNP135 was optimized statistically by response surface methodology for the co-production of xylanase (X) and laccase (L). A significant increase in production of xylanase (2.1-fold, 1,685IU/g) and laccase (2.04-fold, 2,270nkat/g) was observed under optimized conditions viz. pH (10.5), inoculum size (10+10%) and moisture:substrate ratio (0.8:1). Both the enzymes showed identical temperature and pH optima of 70°C and 9, respectively, and were used for deinking of ONP pulp and biobleaching of kraft pulp. In case of ONP pulp deinking, the XL treatment increased brightness (11.8%), freeness (17.8%), breaking length (34.8%), burst factor (2.77%) and tear factor (2.4%). In case of kraft pulp biobleaching, XL treatment showed a significant increase in brightness (13%), whiteness (106.15%) breaking length (49%), burst factor (6.9%), tear factor (23%), and viscosity (11.68%) and reduction in kappa number (15%) after alkali extraction and peroxide stage. This enhancement of pulp properties revealed a synergistic effect of xylanase and laccase produced in one setup.