Journal of Environmental Management 270 (2020) 110914 Available online 20 June 2020 0301-4797/© 2020 Elsevier Ltd. All rights reserved. Research article Transformation of pulp and paper mill sludge (PPMS) into a glucose-rich hydrolysate using green chemistry: Assessing pretreatment methods for enhanced hydrolysis Justin Emmanuel Naicker a, * , Roshini Govinden a , Prabashni Lekha b , Bruce Sithole b, c a University of KwaZulu-Natal (Westville Campus), Discipline of Microbiology, School of Life Sciences, College of Agriculture, Engineering and Sciences, University Road, Westville, Private Bag X 54001, Durban, 4000, South Africa b Council for Scientifc and Industrial Research, Biorefnery Industry Development Facility, PO Box 59081, Umbilo, 4075, South Africa c University of KwaZulu-Natal (Howard Campus), Discipline of Chemical Engineering, College of Agriculture, Engineering and Sciences, Private Bag X 54001, Durban, 4000, South Africa A R T I C L E INFO Keywords: Pulp and paper mill sludge Enzymatic hydrolysis Pretreatment Glucose recovery Valorisation ABSTRACT Pulp and paper mill sludge is a waste stream derived from the pulp and paper making industry, comprised of organic and inorganic material in the form of cellulose, hemicellulose, lignin and ash. In South Africa, approximately fvefour hundred thousand wet tonnes are produced per annum and is currently disposed via landflling or incineration. However, these disposal methods raise environmental and fnancial concerns. This waste stream is an attractive feedstock for fermentable sugars, mainly glucose, recovery and can be redirected for valorisation as a feedstock for microbial fermentation to produce value-added products. Sugar recovery by enzymatic hydrolysis, as opposed to acidic hydrolysis, is a promising approach but is hampered by the lignin and inorganic material found in pulp and paper mill sludge. Several treatment steps to reduce or remove these components prior to enzymatic hydrolysis are assessed in this review. Pretreatment improves hydrolysis of cellulosic fbres and ensures a substantial yield of sugars. 1. Introduction Pulp and paper mill sludge (PPMS), produced by the paper and pulping industry, is an attractive waste product for glucose recovery. Approximately four hundred million wet tonnes of PPMS per annum is produced across the globe; of which the main contributors are Brazil, China, United States of America and Canada producing 17.2 million, 12 million, 5 million and 1.4 million wet tonnes respectively; with South Africa only contributing 0.5 million wet tonnes (Boshoff et al., 2016; Faubert et al., 2016; Mymrin et al., 2016; Veluchamy et al., 2017; Eikelboom et al., 2018). A wide range of disposal methods can be implemented for PPMS including landflling, incineration, gasifcation and pyrolysis (Min et al., 2015). These disposal methods raise envi- ronmental concerns as landflling causes leachate production that con- taminates ground and surface water and incineration emits greenhouse gases, contributing to global warming and may also be accompanied by high energy consumption. Landflling is also becoming expensive because of carbon tax regulations and increased gate fees (Waste: Market Intelligence Report, 2019), moreover in South Africa organic waste that contains �40% moisture can no longer be landflled (Department of Environmental Affairs, 2013). In addition, disposal of PPMS may contribute to disease outbreaks as it can encourage pathogen growth caused by its high organic load, and can exacerbate the envi- ronmental threat due to its composition of ash and trace metals (Kakkar et al., 2018). As a result, alternate environmentally friendly disposal methods of PPMS must be considered to sustain our natural habitat (Veluchamy and Kalamdhad, 2017a). Valorisation approaches for PPMS will not only eliminate its disposal challenges but will also redirect this waste stream into valued-added products. Lignocellulosic biomass, like PPMS, contains ample sugars, mainly glucose, which can be used in microbial fermentations to pro- duce value-added products (Kawaguchi et al., 2016). Four major bio- energy processes can beneft from PPMS as a feedstock; viz. bioethanol, biogas, biohydrogen and biobutanol production; of these bioethanol production has been greatly studied at bench scale (Boshoff et al., 2016; Gottumukkala et al., 2016). Biogases, such as hydrogen and methane, * Corresponding author. E-mail address: jemmanuel777@gmail.com (J.E. Naicker). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: http://www.elsevier.com/locate/jenvman https://doi.org/10.1016/j.jenvman.2020.110914 Received 30 November 2019; Received in revised form 30 April 2020; Accepted 3 June 2020