Pentoses, hexoses and glycerin as substrates for biohydrogen production: An approach for Brazilian biofuel integration

Biofuels production in Brazil is a traditional activity, and it has becoming more important each year. Within this context, biohydrogen production could exploit residual streams from first generation ethanol (ethanol 1G), second generation ethanol (ethanol 2G) and biodiesel production. Therefore hexoses, pentoses and glycerin were tested as substrates for hydrogen production. Firstly, the effects of different inoculum pretreatments (acid, alkaline and heat) on bacterial communitiesʹ performance were evaluated through the levels of Clostridium hydrogenase expression. The heat pretreated inoculum provided the highest yield of H2 (4.62 mol H2/mol sucrose) and also the highest level of hydrogenase expression, 64 times higher when compared with untreated inoculum after 72 h. Then C5 and C6 sugars and also glycerin were tested for H2 production (35 °C and pH 5.5), which resulted in promising yields of H2: sucrose (4.24 mol H2/mol sucrose), glucose (2.19 mol H2/mol glucose), fructose (2.09 mol H2/mol fructose), xylose (1.88 mol H2/mol xylose) and glycerin (0.80 mol H2/mol glycerin).