Biohydrogen Production from Anaerobic Fermentation - Biotechnology in China: Biofuels and Bioenergy - page 150

Fig. 1 General scheme for converting lignocellulosic wastes into hydrogen

38-50% cellulose, 20-35% hemicellulose, and 15-25% lignin [ 48 ], which
potentially can be used as energy sources [ 49 ]. However, because of the complex
structure of lignocellulose, additional processes such as pretreatment, detoxifica-
tion, and hydrolysis are required [ 50 - 52 ]. Figure 1 shows the general scheme for
converting lignocellulosic wastes to biohydrogen.

3.1 Pretreatment

The goal of the pretreatment is to improve the hydrolysis yield and hydrogen
production. Pretreatment methods can be divided into different categories: phys-
ical (milling and grinding), physicochemical (steam explosion, hydrothermolysis,
and wet oxidation, etc.), chemical (alkali, dilute acid, and oxidizing agents),
biological, or a combination of them [ 51 , 53 , 54 ]. Among these methods, physi-
cochemical and chemical pretreatments are frequently applied for enhancing
hydrogen fermentation [ 55 - 59 ]. For example, Fan et al. [ 55 ] investigated hydrogen
production from wheat straw pretreated with HCl, and the maximum cumulative
hydrogen yield of 68.1 ml H 2 /g total volatile solids (TVS) was observed at
126.5 h, which is about a 136-fold increase compared with that from raw wheat
straw. Similar results were also achieved with beer lees waste, and a hydrogen
yield of 68.6 mL H 2 /g TVS was obtained from the biomass pretreated with HCl,
which is an approximately tenfold increase compared with that from the raw
feedstock [ 56 ]. From a practical viewpoint, the ideal pretreatment process
should achieve high yields of fermentable reducing sugars, avoid degradation of
the sugars produced, and avoid the formation of inhibitors of the subsequent
fermentation with respect to minimal use of energy, chemicals, and capital
equipment.