Towards the integration of dark- and photo-fermentative waste treatment. 4. Repeated batch sequential dark- and photofermentation using starch as substrate

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.