Enzyme based deinking for eco friendly recycling of waste paper

Abstract

Domain-3-truncated engineered laccase was employed for eco-friendly recycling of waste paper to achieve 50% reduction in hazardous chemicals usage, without compromising paper properties, under optimized conditions. Engineered laccase pre-treatment followed by 50% chemical treatment achieved increased strength properties of ONP pulp i.e., breaking length, tear factor and burst factor by 17.18, 11.61 and 25%, respectively as compared to 100% chemical treatment which achieved 30.29, 12.46 and 24.13% increase, respectively. A Gram-positive, non-spore forming, yellow pigment producing halophilic bacterium Kocuria rhizophila C60 isolated from compost sample was shown to produce deinking enzyme cocktail comprising cellulase, xylanase and pectinase. Enzyme cocktail pre-treatment reduced the chemical load by 60% while maintaining the same brightness as with 100% chemical treatment. Deinking efficiency of enzyme cocktail + 40% chemical treatment (57.27%) was also higher than 100% chemical treatment (56.10%). In this study, we have also focused on deletion of different domains and the cloning of copper centres from Rheinheimera sp. laccase (RhLacc) to better understand their role in structure-function relationship. Loss of either domain-1 or both domain-1 and domain-2 is responsible for distortion of trinuclear cluster and loss of activity emphasizing most crucial role of trinuclear cluster in laccase activity. Domain-2-truncated engineered laccase was successfully constructed using overlap-extension PCR using linker for fusion of domain-1 and domain-3. This engineered laccase was successfully employed for waste paper recycling and development of enzyme based eco-friendly hair dye. This is the first report on truncation of domain-2 from laccase to obtain an active and functional engineered laccase and established domain-2 s role as a bridge between domain-1 and domain-3 for proper folding and trinuclear cluster formation. This study aims to develop promising native andpaper recycling industries.