Concomitant biohydrogen and poly-β-hydroxybutyrate production from dark fermentation effluents by adapted Rhodobacter sphaeroides and mixed photofermentative cultures

Highlight
• Dark fermentation effluent was valorized via photofermentative H2 and PHB production.
• R. sphaeroides and mixed PNSB cultures were applied.
• H2 (256 mL H2/g COD) and PHB (32.5% DCW) production was achieved from R. sphaeroides.
• More than 70% COD removal from DFE was achieved by mixed PNSB cultures.

This work aimed at investigating concomitant production of biohydrogen and poly-β-hydroxybutyrate (PHB) by photofermentation (PF) using dark fermentation effluents (DFE). An adapted culture of Rhodobacter sphaeroides AV1b (pH 6.5, 24 ± 2 °C) achieved H2 and PHB yields of 256 (±2) N mL H2/g Chemical Oxygen Demand (COD) and 273.8 mg PHB/g COD (32.5 ± 3% of the dry cells weight (DCW)), respectively. When a diluted (1:2) DFE medium was applied to the adapted pure and mixed photofermentative culture, the respective H2 yields were 164.0 (±12) and 71.3 (±6) N mL H2/g COD and the PHB yields were 212.1 (±105.2) and 50.7 (±2.7) mg PHB/g COD added, corresponding to 24 (±0.7) and 6.3 (±0) % DCW, respectively. The concomitant H2 and PHB production from the PF process gave a good DFE post treatment achieving up to 80% COD removal from the initial DFE.

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