Carbohydrates/acid ratios drives microbial communities and metabolic pathways during biohydrogen production from fermented agro-industrial wastewater

The natural fermentation of agroindustrial effluents bottlenecks the dark fermentation processes, diminishing the carbohydrates availability and competing with lactic acid bacteria. To overcome such limitations, hydrogen production from lactate-rich natural fermented agro-industrial wastewater is a promising alternative. This work used model substrates and fermented agro-industrial wastewater to analyze the effect of carbohydrates and lactate/acetate on hydrogen production, the microbial dynamic, and the metabolic pathways. Different carbohydrates/lactic acid ratios were evaluated as substrate, as well as the potential and dynamic of using fermented cheese whey (c.w.) and winery vinasses (w.v.). The model substrate demonstrates that lactic acid and acetate were preferable substrates for hydrogen in terms of potential, rate and yield,1.23 L L−1, 91 mL(L·h)−1, 61.3 mL g CODeq−1; in comparison to using only carbohydrates, 0.26 L L−1, mL(L·h)−1, 12.9 mL g CODeq−1, respectively. This trend was followed when fermented c.w. was used, achieving the highest production rate of 123 mL(L·h)−1. The better hydrogen productivity using c.w. was related to positive interactions between lactic acid bacteria and hydrogen producers like Clostridium. Conversely, negative interactions among hydrogen producers and Acetobacter (acetic acid bacteria) reduced the hydrogen potential using w.v., regardless of its high lactic acid content. A diauxic hydrogen production pattern was observed, where carbohydrates determined the first hydrogen production metabolism, and reduced the metabolism lag associated with lactic acid consumption. This work brings new knowledge about critical microbial interactions and metabolic profiles needed for the energetic valorization of fermented agroindustrial effluents through hydrogen production.