Eleven million tonnes of waste are produced yearly by the European pulp and paper industry, of which 70% originates from the production of deinked recycled paper.Wastes are very diverse in composition and consist of rejects, different types of sludges and ashes in mills having on-site incineration treatment. The production of pulp and paper from virgin pulp generates less waste but the waste has similar properties to waste from the production of deinked pulp, although with less inorganics. Due to legislation and increased taxes, landfills are quickly being eliminated as a final destination for wastes in Europe, and incineration with energy recovery is becoming the main waste recovery method. Other options such as pyrolysis, gasification, land spreading, composting and reuse as building material are being applied, although research is still needed for optimization of the processes. Due to the large volumes of waste generated, the high moisture content of the waste and the changing waste composition as a result of process conditions, recovery methods are usually expensive and their environmental impact is still uncertain. For this reason, it is necessary to continue research on different applications of wastes, while taking into account the environmental and economical factors of these waste treatments.

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Nanocelluloses (NC) increase mechanical and barrier paper properties allowing the use of paper in applications actually covered by other materials. Despite the exponential increase of information, NC have not been fully implemented in papermaking yet, due to the challenges of using NC. This paper provides a review of the main new findings and emerging possibilities in this field by focusing mainly on: (i) Decoupling the effects of NC on wet-end and paper properties by using synergies with retention aids, chemical modification, or filler preflocculation; (ii) challenges and solutions related to the incorporation of NC in the pulp suspension and its effects on barrier properties; and (iii) characterization needs of NC at an industrial scale. The paper also includes the market perspectives. It is concluded that to solve these challenges specific solutions are required for each paper product and process, being the wet-end optimization the key to decouple NC effects on drainage and paper properties. Furthermore, the effect of NC on recyclability must also be taken into account to reach a compromise solution. This review helps readers find upscale options for using NC in papermaking and identify further research needs within this field.

1The use of enzymes has been suggested as an environmentally-friendly alternative to 2 complement conventional chemical deinking in the recycling of recovered paper. This study 3 compares the use of carbohydrate hydrolases versus laccase-mediator system for deinking 4 printed fibers from newspapers and magazines. For this purpose, two commercial enzyme 5 preparations with endoglucanase and endoxylanase activities (Viscozyme Wheat from 6Aspergillus oryzae and Ultraflo L from Humicola insolens) and a commercial laccase 7 (NS51002 from Trametes villosa), the latter in the presence of synthetic or natural (lignin-8 related) mediators, were evaluated. The enzymatic treatments were studied at laboratory scale, 9 using a standard chemical deinking sequence consisting of pulping, alkaline deinking and 10 peroxide bleaching stages. Then, handsheets were prepared and their brightness, residual ink 11 concentration, and strength properties were measured. Among the different enzymatic 12 treatments assayed, both carbohydrate hydrolases were found to deink the secondary fibers 13 more efficiently. Brightness increased up to 3-4% ISO on newspaper fibers, being Ultraflo 14 20% more efficient in the ink removal. Up to 2.5% ISO brightness increase was obtained 15 when magazine fibers were used, being Viscozyme 9% more efficient in the ink removal. As 16 regards laccase-mediator system, alone or combined with carbohydrate hydrolases, it was 17 ineffective deinking both newspaper and magazine fibers, resulting in pulps with worse 18 brightness and residual ink concentration values. However, pulp deinking by laccase-mediator 19 system was displayed when secondary fibers rich in lignin, i.e. printed cardboard, were used, 20 obtaining up to 3% ISO brightness increase and lower residual ink concentrations. 21 22

The recycled paper and board industry needs to improve the quality of their products to meet customer demands. The refining process and strength additives are commonly used to increase mechanical properties. Interfiber bonding can also be improved using cellulose nanofibers (CNF). A circular economy approach in the industrial implementation of CNF can be addressed through the in situ production of CNF using side cellulose streams of the process as raw material, avoiding transportation costs and reducing industrial wastes. Furthermore, CNF fit for use can be produced for specific industrial applications.This study evaluates the feasibility of using two types of recycled fibers, simulating the broke streams of two paper machines producing newsprint and liner for cartonboard, to produce in situ CNF for direct application on the original pulps, old newsprint (ONP), and old corrugated container (OCC), and to reinforce the final products. The CNF were obtained by 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-mediated oxidation and homogenization at 600 bar. Handsheets were prepared with disintegrated recycled pulp and different amounts of CNF using a conventional three-component retention system. Results show that 3 wt.% of CNF produced with 10 mmol of NaClO per gram of dry pulp improve tensile index of ONP ~30%. For OCC, the same treatment and CNF dose increase tensile index above 60%. In both cases, CNF cause a deterioration of drainage, but this effect is effectively counteracted by optimising the retention system.