Enrichment of a Mixed Culture of Purple Non-Sulfur Bacteria for Hydrogen Production from Organic Acids

Hydrogen (H₂) as a clean fuel holds global potential and can be produced through bio-processes. To enhance bioH₂ yields, integrated systems have been proposed, combining dark fermentation (DF) of wastewater with a subsequent photofermentation (PF) stage involving purple non-sulfur (PNS) bacteria. Mixed cultures of PNS bacteria and their microbial ecology have been relatively understudied despite the known benefits of mixed cultures in industrial applications. The aim of this study was to obtain various mixed cultures of PNS bacteria under different environmental conditions during the enrichment stage. Four different mixed cultures were obtained (A, B, C, and D). However, in the H₂ production phase, only Consortium A, which had been enriched with malic acid as the carbon source, exposed to 32 W m⁻² of irradiance, and subjected to intermittent agitation, produced H₂ with a yield of 9.37 mmol H₂ g⁻¹ COD. The consortia enriched were a hybrid of PF and DF bacteria. Especially in Consortium A, Rhodopseudomonas palustris was the dominant organism, and various DF bacteria were positively associated with H₂ production, with their dominance comparable to that of PNS bacteria. Despite the reported low yields, optimizing environmental conditions for this culture could potentially enhance hydrogen production from DF effluents.