Background: A significant fraction of short fibers commonly called "reject fines" is produced while recycling wastepaper at paper mills producing linerboard. These fines are usually rejected into the solid waste stream that further requires land filling and poses environmental problems. The major component of these rejects is cellulose that can be a potential source of fermentable sugars for biofuels, bioplastics or other products. Therefore, a feasible process for converting these reject fines into sugars can profit the paper mills by producing value for their waste products while simultaneously mitigating their adverse environmental impact by avoided solid waste. Additionally, the sugar feedstocks can be used to reduce fossil carbon contributing to the sustainability of the industry.Results: Enzymatic conversion of rejects fines from paper mills was achieved using commercial cellulases from Trichoderma reesei. The presence of mineral particles along with the cellulosic fines was found to have potent inhibitory effects on enzyme hydrolysis. The mineral particles are kaolin and calcium carbonate and originate from the fillers used in the wastepaper. The adsorption of the cellulase onto these mineral components was measured and quantified by the slope of the adsorption isotherm. The application of a nonionic surfactant Tween-80, decreased the adsorption of cellulase and this improved the hydrolysis yield of sugars. Conclusions:Enzymatic hydrolysis of rejects from recycled paper mills is feasible and provides a source of sugars for biofuels and bioplastics. However, the presence of mineral particles can be detrimental to this bioconversion. Calcium carbonate which occurs as a filler in waste paper shows high adsorption affinity to the cellulase enzymes and thus reduces the available enzyme for cellulolysis. This can be remedied by the application of surfactants which preferentially occlude to the mineral surfaces and thus increase enzyme availability in solution. The non-ionic surfactant, Tween-80, shows the best hydrolysis enhancement at a dosage of 3 % based on the dry weight of the biomass.

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