Evaluation of three methods for enriching H2-producing cultures from anaerobic sludge

Hydrogen can be harvested from the microbial fermentation of organic substrates when methanogenesis is suppressed in an anaerobic digestion system. In this study three methods, heat-, acid- and alkaline-treatment, were used to suppress methanogenesis in mixed cultures and to enrich H2-producing inoculum. Highest H2 yield of 2.00 mol-H2/mol-glucose was achieved with the heat-treated sludge, while lowest yield of 0.48 mol-H2/mol-glucose was obtained with the alkaline-treated sludge. A butyrate-type fermentation was found for both heat- and alkaline-treated sludge, while a mixed-type fermentation occurred for the acid-treated sludge. A model was established to describe the kinetics of H2 production process and the yield coefficients of various products were estimated for the three cases with this model. The relationships among NADH/NAD+, oxidation–reduction potential and the H2 partial pressure were established and the evolvement of NADH/NAD+ and oxidation–reduction potential in the fermentative process for the three cases was also evaluated. The comparative experimental results show that the heat-treatment method was better than the two others for enriching H2-producing inoculums from mixed anaerobic cultures.