Biomass and Bioenergy 139 (2020) 105621 Available online 15 June 2020 0961-9534/© 2020 Elsevier Ltd. All rights reserved. Synergistic ultrasound-assisted organosolv pretreatment of oil palm empty fruit bunches for enhanced enzymatic saccharifcation: An optimization study using artifcial neural networks Kiat Moon Lee a, * , Mohd Fauzi Zanil a , Kok Keong Chan a , Zhi Ping Chin a , Yee Chian Liu a , Steven Lim b a Department of Chemical & Petroleum Engineering, Faculty of Engineering, Technology and Built Environment, UCSI University, 56000, Kuala Lumpur, Malaysia b Department of Chemical Engineering, Lee Kong Chian Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, 43000, Selangor, Malaysia A R T I C L E INFO Keywords: Empty fruit bunches Organosolv pretreatment Ultrasound irradiation Delignifcation Process optimization Artifcial neural networks ABSTRACT The effciency of ultrasonic-assisted organosolv in pretreating oil palm empty fruit bunches (EFB) was investi- gated in this study. The effect of temperature, time, sonication power, ethanol concentration and presence of different types of catalysts were examined. The ultrasonic-assisted organosolv pretreatment was found to be signifcantly affected by temperature, time and sonication power. These parameters were further subjected to process optimization study using Leverburgh Marquee artifcial neural networks (ANNs). An empirical model with good predictive accuracies (R-squared value of 0.9084) was generated. From the morphology study, pre- treated EFB showed signifcant structural disruption through the breakage of hemicellulose and lignin bonds, leading to the enhancement of enzymatic saccharifcation. A maximum reducing sugars of 356 mg/g biomass (7.12 g/L) was obtained at optimized conditions of 48.2 � C, 30 min and 55% (192.5 W) sonication power. The relatively high yield of reducing sugars associated with lower lignin content compared to raw EFB also suggested the effectiveness of ultrasonic-assisted organosolv in pretreating EFB. Therefore, this synergistic approach could pave the way for a more effcient and cost-effective pretreatment process for the production of various bio- products and biofuels in the future. 1. Introduction The exploration of renewable and sustainable energies is of global interest in view of the negative effects contributed by non-renewable fossil fuels including its environmental impact and high price vola- tility. One of the renewable sources of energies is lignocellulosic biomass. Lignocellulosic biomass is plant biomass composed of cellu- lose, hemicellulose and lignin. It is a valuable commodity for biofuel production in replacing the fossil fuels due to its low cost and supply abundancy. However, its recalcitrant properties have rendered most bioconversion processes. Therefore, pretreatment step is required to breakdown the complex structure of lignocellulosic biomass so it could be more susceptible to subsequent enzymatic saccharifcation and fermentation for biofuel production. There are various pretreatment techniques available and they are classifed into physical, physiochemical, chemical and biological pretreatments. Chemical pretreatment is reported to be effective in breakdown the biomass structure by decreasing the cellulose crystal- linity and delignifcation [1–3]. As the name implied, chemical pre- treatment involves the usage of chemicals in breaking the biomass. Acid [4,5], alkaline [6,7], ionic liquid [8,9] and organic solvents [10,11] are several of the chemicals used in chemical pretreatment. Organosolv pretreatment which uses organic solvents such as ethanol, methanol and acetone has recently gaining attention from the researchers in view of its environmental benign properties such as low volatility, biodegradability and low toxicity apart for its effectiveness in delignifcation and hemi- cellulose dissolution [12]. Among them, ethanol is the most widely explored solvent due to its low boiling point [13] and less toxicity [14]. Ultrasound irradiation is also one of the emerging technologies in pretreating the lignocellulosic biomass for biofuel production. There are two effects generated by ultrasound irradiation, which are sonochemical and mechanoacoustic effects [15]. Mechanoacoustic effect affects the * Corresponding author. Department of Chemical & Petroleum Engineering, Faculty of Engineering, Technology and Built Environment, UCSI University (Block E) Kuala Lumpur Campus, Jalan Mandarina Damai 1, 56000, Cheras, Kuala Lumpur, Malaysia. E-mail address: leekm@ucsiuniversity.edu.my (K.M. Lee). Contents lists available at ScienceDirect Biomass and Bioenergy journal homepage: http://www.elsevier.com/locate/biombioe https://doi.org/10.1016/j.biombioe.2020.105621 Received 8 July 2019; Received in revised form 21 May 2020; Accepted 24 May 2020