Renewable and Sustainable Energy Reviews 133 (2020) 110338 Available online 11 September 2020 1364-0321/© 2020 Elsevier Ltd. All rights reserved. Dark fermentative hydrogen production from pretreated lignocellulosic biomass: Effects of inhibitory byproducts and recent trends in mitigation strategies Bikram Basak a , Byong-Hun Jeon a, * , Tae Hyun Kim b , Jae-Cheol Lee c , Pradip Kumar Chatterjee d , Hankwon Lim c, ** a Department of Earth Resources & Environmental Engineering, Hanyang University, 222-Wangsimni-ro, Seongdong-gu, Seoul, 04763, Republic of Korea b Department of Materials Science and Chemical Engineering, Hanyang University, Ansan, Gyeonggi-do, 15588, Republic of Korea c School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology, 50 UNIST-gil, Eonyang-eup, Ulju-gun, Ulsan, 44919, Republic of Korea d Energy Research & Technology Group, CSIR-Central Mechanical Engineering Research Institute, Mahatma Gandhi Avenue, Durgapur, 713209, India A R T I C L E INFO Keywords: Dark fermentation Biohydrogen Lignocellulosic biomass Furfural Pretreatment Lignocellulose detoxification ABSTRACT Lignocellulosic biomass (LCB) is expected to play a significant role in achieving the goal of biomass-to-bioenergy conversion due to its wide distribution and low price. Acidogenic dark fermentation of LCB is a promising approach to the sustainable production of biohydrogen (bioH 2 ) from this valuable substrate. Because of its inherent recalcitrance, LCB requires pretreatment to increase its digestibility and enable its improved utilization. Intense thermochemical pretreatments solubilize the lignin and hemicellulose and lead to the formation of a variety of inhibitory byproducts, such as short-chain carboxylic acids, furfural, 5-hydroxymethylfurfural (5- HMF), vanillin, and syringaldehyde, which interfere with the physiological and metabolic functions of dark fermentative microbiota, thus inhibiting bioH 2 production. To offset the negative impacts of these inhibitors on bioH 2 production, approaches to detoxify lignocellulosic hydrolysates have been considered. This review comprehensively discusses the generation of lignocellulosic inhibitory byproducts in commonly used, contem- porary pretreatment regimens and their inhibitory effects on dark fermentative H 2 production. Furthermore, the mechanisms of inhibiting H 2 producing bacteria and their effects on bacterial community dynamics in mixed cultures are reviewed. State-of-the-art strategies for detoxifying pretreated LCB are discussed. The selection of desirable alternative lignocellulose pretreatment strategies that produce less or no inhibitory byproducts are highlighted. Finally, this review discusses the economic aspects of bioH 2 production from LCB, considering the pretreatment and detoxification process. Given the limitations of previous studies, future research for developing cost-effective strategies to overcome byproduct inhibition during dark fermentation of pretreated LCB are suggested. 1. Introduction The increased demand for renewable energy to offset the depletion of fossil fuels and mitigate environmental concerns has required a concerted worldwide effort to produce biofuels from renewable feed- stock. Hydrogen (H 2 ) is a clean, potential energy carrier, as its com- bustion generates only water vapor as a reaction product with a higher energy yield (142 kJ/g) than petroleum-based fuels [1,2]. Biological H 2 production methods stand out as sustainable and environmentally friendly processes in which microorganisms produce H 2 from renewable biomass through dark fermentation (DF) [3,4]. It has been assumed that a considerable amount of renewable energy will be derived from agri- cultural waste, organic waste, and biomass, which potentially represent an abundant renewable and sustainable resource for the production of H 2 energy through DF pathways [5,6]. DF is carried out by many fermentative obligate and facultative anaerobic bacteria which produce molecular H 2 as one of their fermentation end product [7,8]. Due to its high production rate, yield, light-independence, and efficient utilization of various types of organic waste and feedstock as substrates, DF is more suitable for biological H 2 production than photo-fermentation [7,9,10]. * Corresponding author. ** Corresponding author. E-mail addresses: bhjeon@hanyang.ac.kr (B.-H. Jeon), hklim@unist.ac.kr (H. Lim). Contents lists available at ScienceDirect Renewable and Sustainable Energy Reviews journal homepage: http://www.elsevier.com/locate/rser https://doi.org/10.1016/j.rser.2020.110338 Received 23 December 2019; Received in revised form 27 August 2020; Accepted 2 September 2020