Dark fermentation effluent as substrate for hydrogen production from Rhodobacter capsulatus highlighting the performance of different fermentation systems.

Hydrogen production by biological route is a potentially sustainable alternative. Nowadays, energy production from sustainable sources has become urgent for several countries as well as for international policies. In this perspective, hydrogen has gained substantial global attention as clean, sustainable, and versatile energy carrier. In the current work, the resulting effluent from dark fermentation, rich in organic acids, was used as substrate for the purple non-sulfur bacteria (PNS) Rhodobacter capsulatus. In the first stage, experiments were carried out in bioreactors of 50 mL to check the influence of the composition of the effluent dark fermentation. The results proved that the provision of a sugar source improved bio-H2 production. The lactose and lactic acid concentrations exceeding 4.4 and 12 g/L, respectively, resulted in a productivity of up to 37.14 mmol H2/L days. Based on initial conditions obtained on the previous assays, in the second stage, a photo-fermentation in enlarged scale (1.5 L) was performed with the purpose to monitor the production of hydrogen and metabolites, sugar consumption and growth cells during the process. It was observed that the maximum productivity obtained was 98.23 mmol H2/L days in 26 h of process.