Fermentation-pyrolysis of fibre waste from a paper recycling mill for the production of fuel products Logan Jeremy Brown, François–Xavier Collard ⇑ , Lalitha Devi Gottumukkala 1 , Johann Görgens Department of Process Engineering, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa article info Article history: Received 21 May 2020 Revised 27 November 2020 Accepted 28 November 2020 Keywords: Pyrolysis Fermentation Fibre Paper recycling Energy conversion abstract A range of energy fuels (ethanol, char, oil/wax and gas) was produced from fibre waste contaminated with plastic through the application of a fermentation-pyrolysis route. The fibre component was first con- verted to ethanol by simultaneous saccharification and fermentation (SSF), achieving an ethanol concen- tration of 39.8 g/L. The residue, enriched in lignin and plastics, was subjected to fast pyrolysis at temperatures between 350 and 550 °C. A wax product with a higher heating value (HHV) higher than 28 MJ/kg was obtained for temperatures higher than 450 °C, while values lower than 15 MJ/kg were observed for the oils produced from the untreated waste stream. Pyrolysis at 550 °C produced a wax with an HHV as high as 32.1 MJ/kg, where 51.8% of the energy content of the fermentation residue was trans- ferred. The attractive energy contents of the pyrolysis products were enabled by oxygen removal from the feedstock during fermentation to ethanol. Ó 2020 Elsevier Ltd. All rights reserved. 1. Introduction The potential of industrial waste to contribute to energy secu- rity and the need for more sustainable approaches have strength- ened the interest in waste-to-energy technologies as alternatives to disposal at landfill sites (Arenales Rivera et al., 2016; Gottumukkala et al., 2016). The utilisation of industrial waste streams rich in lignocellulosic biomass represents a potential untapped source for the production of fuels, thereby reducing the dependency on fossil resources. The paper industry currently produces large quantities of waste that can be grouped into two main categories, namely paper waste sludge (PWS) and rejects. PWS is comprised predominately of degraded fibres. Rejects originate from the primary processing/ screening activities in paper mills making use of recycled fibres as feedstock; these occur before the paper machine and produce rejects composed of degraded fibres, plastics and other contami- nants (Arenales Rivera et al., 2016; Brown et al., 2017; Gottumukkala et al., 2016; Méndez et al., 2009). Various rejects streams are obtained at different steps of the pulping and screen- ing processes before the paper machine, with the streams gener- ated at the early steps having higher plastic content. Fibres in paper waste sludge (PWS) have been shown to be an effective feedstock for the production of bioethanol (Boshoff et al., 2016; Zhang and Lynd, 2010), as the crystalline structure of the cellulose has been degraded by mechanical and chemical pulping during the manufacturing process, which increases cellu- lose accessibility for enzymatic hydrolysis (Boshoff et al., 2016; Gottumukkala et al., 2016). Hydrolysis-fermentation are integrated into one process step by simultaneous saccharification and fer- mentation (SSF) (Gottumukkala et al., 2016; Lynd et al., 2002), where the glucose released during enzymatic hydrolysis is utilised by the yeast. As a result there is no feedback inhibition of the enzymes, which increases the final ethanol yield (Dwiarti et al., 2012). Recent studies on SSF of PWS have reported ethanol concen- tration above the threshold value for economic viability of 40 g/L from low and intermediate ash PWS (Boshoff et al., 2016; Gottumukkala et al., 2016) at relatively high solids loading (>20 wt%). Such conversion results in the formation of a residue with an increased lignin content that can reach 34 – 39 wt% (on dry ash free basis) (Boshoff et al., 2016). Rejects as waste also contain degraded fibres that can no longer be used in the manufacturing of board or paper, similar to PWS, thus making it a potential source to produce bioethanol by SSF. Based on the rejects composition, such conversion should leave behind a residue richer in lignin and plastics, making it suitable as a feedstock for thermochemical conversion, such as pyrolysis. Pyrolysis is the means of thermally degrading a feedstock in a sin- gle step at temperatures generally in the range of 400–600 °C and https://doi.org/10.1016/j.wasman.2020.11.055 0956-053X/Ó 2020 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: fcollard@sun.ac.za (F. Collard). 1 Present address: Celignis Limited, Limerick Ireland. Waste Management 120 (2021) 364–372 Contents lists available at ScienceDirect Waste Management journal homepage: www.elsevier.com/locate/wasman