Biomass and Bioenergy 134 (2020) 105486 Available online 5 February 2020 0961-9534/© 2020 Elsevier Ltd. All rights reserved. Synergistic effect of humic acid on alkali pretreatment of sugarcane bagasse for the recovery of lignin with phenomenal properties R. Uma Maheswari a , Musthafa O. Mavukkandy b , Utpal Adhikari c , Vincenzo Naddeo d , Jaya Sikder a, ** , Hassan A. Arafat b, * a Department of Chemical Engineering, National Institute of Technology Durgapur, West Bengal, 713209, India b Center for Membrane and Advanced Water Technology, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates c Department of Chemistry, National Institute of Technology Durgapur, West Bengal, 713209, India d Sanitary Environmental Engineering Division (SEED), Department of Civil Engineering, Uiversit� a Degli Studi di Salerno, Fisciano, SA, Italy A R T I C L E INFO Keywords: Bagasse Humic acid Lignin recovery Fragmentation Enzymatic hydrolysis Fermentation ABSTRACT Lignin forms a recalcitrant structure in lignocellulosic biomass and hence huge amount of enzymes are required for disintegrating it into their subsequent components, like glucose and other by-products. Thus, the pretreat- ment is an ineluctable step in the bioethanol scheme for the delignifcation of biomass and also the recovery of lignin, an emerging value added polymer in many industrial applications. A green facile method was developed wherein humic acid (HA) acts as a catalyst and surfactant in the alkali pretreatment of sugarcane bagasse for the step reduction in lignin recovery scheme with phenomenal properties and enhanced enzymatic-hydrolysis. HA assisted experiments were performed with and without calcium chloride (CaCl 2 ). Effective disintegration of lignocellulose by the cleavage of β-O-4 moieties resulted in forming lignin and hydrolyzable biomaterial via two pathways. Possible covalent linkages between the HA and lignin resulted in the release of esters as a byproduct. Thus, the delignifed biomass, the isolated lignin and a variety of esters, could be valorised in various industrial applications. The biomass was characterized by XRD and SEM analysis. The isolated lignin was characterized using FTIR, NMR, GPC, SEM, and TGA – DTA studies. The yield of recovered pure lignin for the two process was 90–100%, as measured through gravimetric analysis. The produced esters were confrmed using FTIR studies. Batch enzymatic hydrolysis was performed for the HA assisted de-lignifed bagasse (without CaCl 2 ), which demonstrated a 19% increase in glucose yield compared to the alkali treated bagasse. The produced hydrolysates were subjected to fermentation for the production of ethanol. 1. Introduction Lignocellulosic biomass refers to plant dry matter consisting of cel- lulose, hemicellulose, and lignin [1]. These materials are renewable, cheap and abundant [2,3]. Due to the rapid depletion of fossil fuels, conversion of lignocellulosic biomass into biofuels via fermentable sugars has received considerable attention [4,5]. Sugarcane is a native of countries of warm climate and is found abundantly in tropical regions such as Brazil, India, South America, Asia Pacifc, etc. [6]. Leftover from the sugarcane juice extract, sugarcane bagasse, is rich in fber. Dried sugarcane bagasse contains cellulose (26–50%), hemicellulose (24–34%) and lignin (10–26%) [7]. Lignocellulosic biomass has a robust structure because of the high crystallinity of cellulose and hydrophobicity of lignin, together with the enclosure of cellulose within a lignin-hemicellulose matrix. Fermentable sugars could be obtained from that cellulose via enzymatic hydrolysis [8]. But lignin hinders the accessibility of cellulase to cellulose and ineffectively consumes the cellulase [9–11]. Therefore, appropriate pre-treatment of biomass, by altering its physicochemical properties, is required to promote the bioavailability of cellular matrix [12–14]. In a typical pretreatment phase, sugarcane bagasse is disintegrated down to its sub-components and lignin is extracted prior to the enzymatic hy- drolysis. Usual pretreatment schemes include steam explosion, me- chanical comminution, chemical treatment and subsequent heating and fungal treatment [15,16]. The evaluation of a pretreatment method is based on techno-economic criteria, such as the cost and recycling * Corresponding author. ** Corresponding author. E-mail addresses: jaya.sikder@che.nitdgp.ac.in (J. Sikder), hassan.arafat@ku.ac.ae (H.A. Arafat). Contents lists available at ScienceDirect Biomass and Bioenergy journal homepage: http://www.elsevier.com/locate/biombioe https://doi.org/10.1016/j.biombioe.2020.105486 Received 6 June 2019; Received in revised form 23 January 2020; Accepted 27 January 2020