Fermentative hydrogen production from agroindustrial lignocellulosic substrates

To achieve economically competitive biological hydrogen production, it is crucial to consider inexpensive materials such as lignocellulosic substrate residues derived from agroindustrial activities. It is possible to use (1) lignocellulosic materials without any type of pretreatment, (2) lignocellulosic materials after a pretreatment step, and (3) lignocellulosic materials hydrolysates originating from a pretreatment step followed by enzymatic hydrolysis. According to the current literature data on fermentative H(2) production presented in this review, thermophilic conditions produce H(2) in yields approximately 75% higher than those obtained in mesophilic conditions using untreated lignocellulosic substrates. The average H(2) production from pretreated material is 3.17 ± 1.79 mmol of H(2)/g of substrate, which is approximately 50% higher compared with the average yield achieved using untreated materials (2.17 ± 1.84 mmol of H(2)/g of substrate). Biological pretreatment affords the highest average yield 4.54 ± 1.78 mmol of H(2)/g of substrate compared with the acid and basic pretreatment - average yields of 2.94 ± 1.85 and 2.41 ± 1.52 mmol of H(2)/g of substrate, respectively. The average H(2) yield from hydrolysates, obtained from a pretreatment step and enzymatic hydrolysis (3.78 ± 1.92 mmol of H(2)/g), was lower compared with the yield of substrates pretreated by biological methods only, demonstrating that it is important to avoid the formation of inhibitors generated by chemical pretreatments. Based on this review, exploring other microorganisms and optimizing the pretreatment and hydrolysis conditions can make the use of lignocellulosic substrates a sustainable way to produce H(2).