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Both dark and photo-fermentation can be used for biological hydrogen production; either performed separately, in two-stage systems, or in co-culture. A single stage process is less laborious and costly; however, the two types of microorganisms have different nutritional requirements requiring optimization of culture conditions. Here a response surface methodology (RSM) with a Box-Behnken design was used to optimize microorganism ratio and substrate and buffer concentrations, and to evaluate their interactive effects for maximization of hydrogen yield. Clostridium butyricum and Rhodopseudomonas palustris were grown on a potato starch/glucose base medium at 30 degrees C under continuous illumination (40 W m(-2) light intensity). The highest hydrogen yield, 6.4 +/- 1.3 mol H-2/mol glucose, was obtained with a substrate concentration of 15 g/L, buffer concentration of 50 mM, and microorganism ratio of 3. The observed strong interaction between buffer and substrate concentration is most likely due to the need to optimize the pH for co-cultures. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Hydrogen can be produced via dark and photo-fermentation using either single-stage or two-stage processes. The advantage of a two-stage system is that it is possible to separately optimize and control culture conditions for the dark and photo-fermentative bacteria. In the present study a mixture of starch and glucose was used as carbon source for the dark fermentation step. Response surface methodology (RSM) with a Box-Behnken design (BBD) was applied to the photo-fermentation stage for the optimization of key parameters: inoculum concentration (Rhodopseudomonas palustris), substrate concentration (dark fermentation effluent (DFE)) and pH. In this sequential two-stage system, the highest overall hydrogen yield (8.3 +/- 0.1 mmol H-2/gCOD), overall hydrogen production (1.62 mmol) and the photo fermentation yield (7.21 +/- 0.2 mmol H-2/gCOD) were achieved at inoculum of 9 mL (1.64 +/- 0.7 x 10(8) cells), a DFE dilution of 2.5x and a pH of 7.5, which were center points of the design. 97% COD removal was achieved at the highest dilution of DFE (lowest concentration of carbon source) at pH 6.5. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Biohydrogen production from cellulose by a bacterial co-culture is a potentially promising approach for producing bioenergy from a low cost substrate. The use of a cellulolytic bacterium, Cellulomonas fimi, permits cellulose conversion and the in situ production of substrate for growth and hydrogen production by the photosynthetic bacterium Rhodopseudomonas palustris. Response surface methodology (RSM) with a Box-Behnken design (BBD) was used to examine variations in the key parameters: substrate (cellulose) concentration, yeast extract concentration and the microorganism ratio (Rps. palustris/C. fimi). For the co-culture of R. palustris and C. fimi the highest hydrogen production (44 mmol H-2/L) was achieved at the highest substrate concentration (5 g/L); however, the highest hydrogen yield (3.84 mol H-2/mol glucose equivalent) was observed at the lowest cellulose concentration and highest microorganism ratio. High COD removal efficiencies, over 70%, were achieved over a wide range of conditions and were positively affected by the concentration of yeast extract. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Hydrogen yields of dark fermentation are limited due to the need to also produce reduced side products, and photofermentation, an alternative, is limited by the need for light. A relatively new strategy, dark microaerobic fermentation, could potentially overcome both these constraints. Here, application of this strategy demonstrated for the first time significant hydrogen production from lactate by a single organism in the dark. Response surface methodology (RSM) was used to optimize substrate and oxygen concentration as well as inoculum using both (1) regular batch and (2) O-2 fed batch cultures. The highest hydrogen yield (HY) was observed under regular batch (1.4 +/- 0.1 mol H-2/mol lactate) and the highest hydrogen production (HP) (173.5 mu mol H-2) was achieved using O-2 fed batch. This study has provided proof of principal for the ability of microaerobic fermentation to drive thermodynamically difficult reactions, such as the conversion of lactate to hydrogen.