Biohydrogen production from lignocellulosic feedstock Chieh-Lun Cheng a , Yung-Chung Lo a , Kuo-Shing Lee b , Duu-Jong Lee c , Chiu-Yue Lin d , Jo-Shu Chang a,e,f,g,⇑ a Department of Chemical Engineering, National Cheng Kung University, Tainan 701, Taiwan b Department of Safety Health and Environmental Engineering, Central Taiwan University of Science and Technology, Taichung, Taiwan c Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan d Department of Environmental Engineering and Science, Feng Chia University, Taichung, Taiwan e Center for Bioscience and Biotechnology, National Cheng Kung University, Tainan, Taiwan f Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan, Taiwan g Sustainable Environment Research Center, National Cheng Kung University, Tainan, Taiwan article info Article history: Received 15 January 2011 Received in revised form 18 April 2011 Accepted 19 April 2011 Available online 27 April 2011 Keywords: Biohydrogen Cellulases Lignocellulosic feedstock Saccharification Pretreatment abstract Due to the recent energy crisis and rising concern over climate change, the development of clean alter- native energy sources is of significant interest. Biohydrogen produced from cellulosic feedstock, such as second generation feedstock (lignocellulosic biomass) and third generation feedstock (carbohydrate-rich microalgae), is a promising candidate as a clean, CO 2 -neutral, non-polluting and high efficiency energy carrier to meet the future needs. This article reviews state-of-the-art technology on lignocellulosic biohy- drogen production in terms of feedstock pretreatment, saccharification strategy, and fermentation tech- nology. Future developments of integrated biohydrogen processes leading to efficient waste reduction, low CO 2 emission and high overall hydrogen yield is discussed. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Today’s global energy supply depends heavily on fossil fuels, although significant efforts are being made worldwide to use non-carbonaceous fuels produced from renewable feedstock, as these have fewer greenhouse gas emissions during both fuel pro- duction and combustion. Hydrogen has emerged as one of the most promising new energy carriers, because it is clean, recyclable, effi- cient, and can be used in fuel cells to directly generate electricity (Das and Vezirog ˘lu, 2001). The major obstacle to the commercial- ization of bioH 2 is the high production cost, and thus there is an ur- gent need to come up with strategies that could make it more economically feasible. One of the ways to lower the bioH 2 production cost is to use cheap and renewable feedstock, such as lignocellulosic materials (e.g., agricultural residues, paper wastes and wood chips), which are both abundant and sustainable. Asian countries possess signif- icant potential for producing bioenergy from crop residues. In Tai- wan, rice straw is the major agricultural waste, and is suitable for use as the feedstock for the production of bioenergy (such as H 2 ). However, cellulosic materials are usually not readily fermentable by microorganisms because of their complex structure that is resis- tant to enzymatically hydrolytic attacks. The factors affecting enzy- matic hydrolysis include the porosity and crystallinity of lignocellulosic materials and the lignin content. Pretreatment is thus usually required to remove lignin, reduce the crystallinity of cellulose and increase the surface area of the material to enhance the formation of sugars for further applications in biofuels produc- tion (Xia and Sheng, 2004). Formation of soluble sugars from cellu- lose in agricultural residues relies on the sequential/coordinated action of individual enzyme components, mainly endoglucanase, exoglucanase, b-glucosidase, and xylanase, which are widely ob- served among various bacterial and fungal strains (Amouri and Gargouri, 2006). Lignocellulosic hydrolysate containing higher amounts of monomeric sugars (mainly glucose and xylose) can be further used for the production of hydrogen, ethanol, and other high-valuable chemicals (Xia and Sheng, 2004). A major challenge of cellulosic hydrogen production is how to convert the carbohydrates in the lignocellulosic feedstock into fer- mentable sugars in an efficient and cost-effective manner. In gen- eral, pretreatment of raw lignocellulosic materials is employed, followed by hydrolysis of cellulose and hemicellulose into sugars that can be directly fermented to produce biohydrogen. The pre- treatment process is usually energy intensive or requires using hazardous chemicals, while a large amount of expensive enzymes are needed in the hydrolysis step. This can significantly increase the production cost of lignocellulosic biohydrogen, thereby limit- ing its commercial applications. Therefore, it is necessary to devel- 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.04.059 ⇑ Corresponding author at: Department of Chemical Engineering, National Cheng Kung University, Tainan 701, Taiwan. Fax: +886 6 2357146/2344496. E-mail address: changjs@mail.ncku.edu.tw (J.-S. Chang). Bioresource Technology 102 (2011) 8514–8523 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech