Dark fermentative bio-hydrogen production: Effects of substrate pre-treatment and addition of metal ions or L-cysteine

Abstract

H2 is regarded as a promising energy resource because of its high energy content (122kJ/g), and since capable of replacing fossil energy sources. To enhance the hydrogen production, two pure bacterial strains were jointly applied as mixed cultures in a single fermenter, thus combining the starch hydrolysis process and H2 production process. Strain A1 was responsible for starch hydrolysis by producing amylase and strain B1 was in charge of hydrogen production. Since the starch pre-treatment conduces to starch hydrolysis and the metal ions are the important elements of hydrogenase, the hydrogen production using corn starch was moreover assessed when either pre-treating the starch feed, or by adding Fe2+ or Mg2+, possibly in association with L-cysteine. The cumulative H2 production increased as average of triplicate experiments from 838 to 1186mL when the corn starch was pre-treated by boiling. The H2 production rate of pre-treated corn starch was much higher than that of untreated corn starch. The H2 yield of pre-treated corn starch reached 1.19mol H2/mol glucose, 40% higher than using untreated corn starch (0.85mol H2/mol glucose). By adding trace elements (Fe2+ and Mg2+) and L-cysteine, the H2 yields were higher than for the control, except when adding Mg2+. The enhancement of the H2 production by the sole addition of Fe2+ and L-cysteine was significant (by 105% and 60%, respectively). The sole addition of Fe2+ to the system had the highest effect with a maximum cumulative H2 production of 1928mL and H2 yield of 1.94mol H2/mol glucose.