Hydroxytyrosol rich-mixture from olive mill wastewater and production of green products by feeding Rhodopseudomonas sp. S16-FVPT5 with the residual effluent.

This study disserts on the exploitation of olive mill wastewater (OMW) for the production of both bio-based poly-β-hydroxybutyrate (PHB) and hydrogen (H) by using the residual effluent as feedstock for growing purple bacteria after the recovery of hydroxytyrosol-rich mixtures. In particular, Rhodopseudomonas sp. S16-FVPT5 was fed with either the virgin OMW or dephenolized-OMW (d-OMW). For polyphenols removal, the OMW was treated with activated carbon; subsequently, acidified ethanol (pH = 3.1) at 50 °C was used as extractor solvent for obtaining hydroxytyrosol-rich mixtures. The maximum hydroxytyrosol content in the resultant polyphenolic mixture was 2.02 g/L. The highest co-production of PHB (315 mg PHB/L) and H (2236 mL H/L) were achieved feeding Rhodopseudomonas sp. S16-FVPT5 with pure d-OMW. The highest hydrogen yield (4.55 L(H)/L) was obtained feeding the bacterium with d-OMW, diluted at 25%; by increasing the content of d-OMW into the culture broth the hydrogen yield progressively decreased. Lower results were obtained by feeding the bacterium with a synthetic medium, the cumulative hydrogen was 1855 mL H/L); the PHB was 101 mg PHB/L. The highest theoretical light conversion efficiency was 2.36% with the synthetic medium and 1.99% when feeding Rhodopseudomonas sp. S16-FVPT5 with d-OMW diluted with water 50%, v/v.