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Purple non-sulfur bacteria generate hydrogen and polyhydroxybutyrate (PHB) as a mechanism for disposing of reducing equivalents generated during substrate consumption. However, both pathways compete for the reducing equivalents released from bacteria growing under certain substrates, thus the formation of hydrogen or PHB is detrimental to the formation of each other. The effect of mixtures of acetic, propionic and butyric acids on the formation of H and PHB was evaluated using Box-Behnken design. A bacterial community mainly constituted by Rhodopseudomonas palustris was used as inoculum. It was observed that the three volatile fatty acids had a significant effect on the specific PHB production. However, only the propionic acid had a significant effect on the specific H production activity and the highest value was observed when acetate was the main component in the mixture. The maximum values for the specific PHB and hydrogen production rates were 16.4 mg-PHB/g-TSS/day and 391 mL-H/g-TSS/day, respectively.

BACKGROUND Food waste is a valuable source of hydrogen by dark fermentation. Dark fermentation effluent contains volatile fatty acids that can be further converted into more hydrogen using microbial electrolysis cells (MECs). In this process, the anodic potential (Ean) has a significant influence on the MEC performance as well as the effluent composition. The objective of this study was to evaluate the effects of variation of the anode potential and substrate composition (food waste fermentation effluent) on the performance of hydrogen production using two‐chamber MECs. RESULTS Colonization was conducted using an Ean of 0.5 V vs Ag/AgCl. After 38 days, the Ean had decreased to 0.3 V, resulting in an increase in the hydrogen production rate (from 287 to 482 mL H2 L‐1cat d‐1). A maximum hydrogen production rate of 685 mL H2 L‐1cat d‐1 was observed when effluent that contained the highest acetate concentration was utilized. Cathodic hydrogen recovery was higher than 93%, and hydrogen yield was greater than 873 mL H2 g‐1 COD. CONCLUSION The start‐up strategy in which Ean is decreased after the formation of an electroactive biofilm resulted in increased hydrogen production. The composition of the food waste fermented effluent influences the hydrogen production rate. © 2017 Society of Chemical Industry

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