Contents lists available at ScienceDirect Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop Recovery and characterisation of cellulose from industrial paper mill sludge using tetrakis and imidazolium based ionic liquids Katarzyna Glińska a , Muhammad Solehin Bin Ismail a , Jordi Goma-Camps b , Pau Valencia b , Frank Stüber a , Jaume Giralt a , Azael Fabregat a , Esther Torrens a , Magdalena Olkiewicz a , Christophe Bengoa a, ⁎ a Chemical Engineering Department, Universitat Rovira i Virgili, Avinguda dels Països Catalans 26, 43007, Tarragona, Spain b Goma-Camps, S.A.U., Carrer Cardenal Gomà, 29, 43450, La Riba, Spain ARTICLE INFO Keywords: Cellulose Recovery Green solvents Industrial paper mill wastewater Ionic liquid Sludge valorisation ABSTRACT Paper industry is a sector that generates large volumes of wastewater and sludge. There is a possibility to recover the cellulose contained in these effluents. Two tetrakis and imidazolium based commercial ionic liquids were used to recover the cellulose from industrial paper dried sludge. Both ionic liquids were able to recover the cellulose of the sludge (˜100%). The ratio sludge:ionic liquid had only a low influence on the recovery. The mass of cellulose recovered was the same for both ionic liquids. The tetrakis ionic liquid was able to clean the pre- cipitate better, eliminating a major quantity of ashes. The imidazolium ionic liquid was able to leave a minor quantity of initial proteins in the precipitate. These encouraging results demonstrate that the recovery of cel- lulose from paper industry sludge is feasible with ionic liquids. But, improvement of the performances of the ionic liquids is necessary to allow a scale-up of the technology. 1. Introduction Paper industry is one of the major users of water; in fact, it occupies the third position (Buruberri et al., 2015). It is also one of the industries which apply the concept of circular economy, where material streams maintain added values for as long as possible (Deviatkin et al., 2016). The European pulp and paper industry replaces up to 72% of virgin fibre with recovered paper, normally from municipal and industrial selective garbage collection. Taking into account that 22% of the paper cannot be recovered, the limit will be attained soon (European Re- covered Paper Council, 2014). The world production of paper in 2015 was 400 million tons, 83 million in 2017 in Europe. Previsions are about 550 million tons in 2050 (Faubert et al., 2016). The utilisation of recovered paper implies cleaning it. The deinking process generates 150 kg of dry solids by ton of produced paper (Deviatkin et al., 2016). Production of virgin pulp and deinking activities generate large vo- lumes of wastewater, which is called paper mill wastewater. The pro- duction of this wastewater is considered to be between 1.5 and 60 m 3 per day per ton of paper produced (Adhikari and Bhattacharyya, 2015). The management of this huge amount of wastewater has a great impact on the environment and requires treatment before its disposal. One of the typical solutions is incineration, which has a high economic cost due to its high-water content and emission of greenhouse gases (Faubert et al., 2016). Other possibilities are disposal in agriculture as fertilizer, production of bioethanol or production of new materials (Farghaly et al., 2017). In fact, this situation is not used anymore and, for this reason, the European Community published the European framework directive on waste (2008/98/EC): “This Directive lays down measures to protect the environment and human health by preventing or redu- cing the adverse impacts of the generation and management of waste and by reducing overall impacts of resource use and improving the efficiency of such use”. The directive established a hierarchy of actua- tion, prioritising prevention of waste; re-use of waste; recycling; other recovery, e.g. energy recovery; and finally, disposal. This provoked a change in the usual management of paper mill wastewater. From the beginning, the directive was supported by the Confederation of Eur- opean Paper Industry (CEPI, www.cepi.org). On the other hand, the European Commission Roadmap to Resource Efficient Europe (COM (2011) 571) envisages Europe economical sus- tainability by 2050, by preconizing that waste must be primarily managed as a new resource. Also, utilisation of these wastes as energy vectors is forbidden, allowing it only for non-recyclable materials, and some of these achievements must be completed by 2020 (Molina- Sánchez et al., 2018). This recommendation incited to use paper mill https://doi.org/10.1016/j.indcrop.2019.111556 Received 22 March 2019; Received in revised form 21 June 2019; Accepted 9 July 2019 ⁎ Corresponding author. E-mail address: christophe.bengoa@urv.cat (C. Bengoa). Industrial Crops & Products 139 (2019) 111556 0926-6690/ © 2019 Elsevier B.V. All rights reserved. T