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Abstract: Eight natural microbial consortia collected from different sites were tested for dark, hydrogen production during starch degradation. The most active consortium was from silo pit liquid under mesophilic (37°C) conditions. The fermentation medium for this consortium was optimized (Fe, NH4 +, phosphates, peptone, and starch content) for both dark fermentation and for subsequent purple photosynthetic bacterial H2 photoproduction [Laurinavichene TV, Tekucheva DN, Laurinavichius KS, Ghirardi ML, Seibert M, Tsygankov AA. Towards the integration of dark and photo fermentative waste treatment. 1. Hydrogen photoproduction by purple bacterium Rhodobacter capsulatus using potential products of starch fermentation. Int J Hydrogen Energy 2008;33(23):7020–26], in the presence of the spent dark, fermentation effluent. The addition of Zn (10 mg L−1), as a methanogenesis inhibitor that does not inhibit purple bacteria at this concentration, also did not inhibit dark, fermentative H2 production. The influence of various fermentation end products at different concentrations (up to 30gL−1) on dark, H2 production was also examined. Added lactate stimulated, but added isobutyrate and butanol strongly inhibited gas production. Under optimal conditions the fermentation of starch (30gL−1) resulted in 5.7LH2 L−1 of culture (1.6mol H2 per mole of hexose) with the co-production mainly of butyrate and acetate. [Copyright &y& Elsevier]

Abstract: In this study we demonstrated the technical feasibility of a prolonged, sequential two-stage integrated process under a repeated batch mode of starch fermentation. In this durable scheme, the photobioreactor with purple bacteria in the second stage was fed directly with dark culture from the first stage without centrifugation, filtration, or sterilization (not demonstrated previously). After preliminary optimization, both the dark- and the photo-stages were performed under repeated batch modes with different process parameters. Continuous H2 production in this system was observed at a H2 yield of up to 1.4 and 3.9 mole mole−1 hexose during the dark- and photo-stage, respectively (for a total of 5.3 mole mole−1 hexose), and rates of 0.9 and 0.5 L L−1 d−1, respectively. Prolonged repeated batch H2 production was maintained for up to 90 days in each stage and was rather stable under non-aseptic conditions. Potential for improvements in these results are discussed. [Copyright &y& Elsevier]

Abstract: In this study, the H2-photoproduction capacity of Rhodobacter capsulatus B10 was measured as a function of variations in the nature and concentration of volatile fatty acids (VFAs) and other products of dark fermentation. When an equimolar mixture of VFAs was provided, C4 substrates (butyrate and isobutyrate) were not consumed until the C2–C3 substrates (acetate, propionate, and lactate) became unavailable, but in order for the cells to produce H2 at high rates they could not be exposed to severe growth substrate depletion. Among other possible fermentation products, the highest inhibition was observed by the addition of butanol (50% inhibition at 50mM). The influence of high concentrations of VFAs, phosphate (used to stabilize the pH during dark fermentation) and some heavy metals (known inhibitors of methanogenesis) was also shown. Based on the results, the conditions of fermentation can be manipulated to avoid the inhibition of subsequent H2 photoproduction by photosynthetic bacteria. [Copyright &y& Elsevier]