Biobleaching of wheat straw rich-soda pulp by the application of thermophilic mannanase from Bacillus sp. MG-33

Thermophilic mannanase from the Bacillus sp. MG-33 was applied on wheat straw-rich-soda pulp to evaluate its bleaching potential. Optimum conditions for bio-bleaching of pulp were found as, mannanase 3Ug -1 of pulp at pH 6.5 and temperature 65oC that enhanced the brightness by 30% and reduced the kappa number by 20% within 2h. Tear index (1.1, points) and burst index (0.02, points) were also improved by mannanase-treated pulp as compared to the untreated pulp. Treatment of chemically (CEHIHII) bleached pulp with an enzyme showed significant effect on release of chromophores, hydrophobic and reducing compounds. Mannanase-prebleaching of raw pulp reduced the use of hypochlorite by 28% to achieve brightness of resultant hand sheets similar to the fully chemically bleached pulp. Scaning electron microscopic studies of mannanase treated pulp distinctly revealed that separation of microfibers which assist in lowering down the chemical requirement in the subsequent chemical bleaching.