Biological deinking technology for the recycling of office waste papers

Results of the enzymatic deinking approach were demonstrated on a laboratory scale to provide a good quality deinked pulp from laser-printed alkaline office paper wastes. It has been suggested that, for alkaline papers, the majority of inks are localised on the paper coatings and fillers consisting mainly of CaCO3. Enzyme treatment improved by stock acidification and dissolution of CaCO3 prior to flotation resulted in effective detachment and dispersion of toner specks ensuring a high deinking effectiveness. Highly dispersed toner particles separation was promoted by acidic flotation in the presence of a surfactant, hydrocarbon oil, applied to improve microink agglomeration and hydrophobicity of the toner particles and agglomerates. A minimal level of visible dirt was observed for optimised enzyme-treated and acidically floated pulps. Both enzyme preparations significantly favoured deinking effectiveness relative to control stocks. Only minor differences were observed between cellulase and resinase (lipase) preparations. The lowering of pH prior to flotation considerably improved the cleanliness not only of the enzyme-treated, but also the control pulps relative to alkaline floated stocks. The addition of an appropriate surfactant, such as hydrocarbon oil proved to be a necessary factor to prevent redeposition of microink particles on the fibre surfaces and promote the separation of highly dispersed toner particles from the fibre network.