Potential of in situ SSF laccase produced from Ganoderma lucidum RCK 2011 in biobleaching of paper pulp

Production of laccase from Ganoderma lucidum RCK 2011 under solid-state fermentation (SSF) conditions was optimized using response surface methodology, resulting in an approximate eightfold increase compared to that in the unoptimized media. Further, the enzyme produced under SSF as whole fermented substrate (in situ SSF laccase) was found to be more stable than the in vitro enzyme (harvested by downstreaming processing of fermented wheat bran). Interestingly, the biobleaching potentials of both in situ and in vitro SSF laccases were comparable, saving 25% chlorine dioxide for achieving similar pulp brightness as obtained in the pulp treated chemically. The reduction in the demand of chlorine dioxide in the pulp bleaching sequence subsequently decreased the levels of adsorbable organic halogen (AOX) in the resulting effluents of the process by 20% compared to the effluents obtained from chemical bleaching sequence. Therefore, direct application of in situ SSF laccase in pulp biobleaching will be environmentally friendly as well as economical and viable for implementation in paper mills.