Optimization of the bio-H₂ and lactate production from vinasse and molasses: an experimental approach for the bioenergy development in Brazil

This study investigates the efficiency of hydrogen (H₂) and lactate (HLa) generation in the co-fermentation of sugarcane vinasse and molasses, aiming to optimize operational strategies through central composite design (CCD) and response surface methodology (RSM). The tests were conducted in 1 L Duran® flasks, with a working volume of 500 mL, under thermophilic conditions (55°C) and pH 7.0. Nine conditions were evaluated by varying co-substrate concentrations (3.9 - 11.1 g COD.L⁻¹) and vinasse proportions (7.6 - 92.4%), identifying the most favourable conditions for H₂ and HLa production. High H₂ potential (up to 1275 mL.L⁻¹) was observed with 7.5 g COD.L⁻¹ of co-substrates and 7.6% vinasse, mainly attributed to <i>Clostridium</i>. Adding molasses maximized H₂ generation, while higher vinasse proportions favoured lactobacilli, increasing HLa concentration and reducing H₂. Replicability was ensured, validating tests with high H₂ generation and 75% similar results. The tests showed discrepancies in bacterial genus prevalence: the condition with 11.1 g COD.L⁻¹ of co-substrates and 50% vinasse favoured HLa producers (<i>Sporolactobacillus</i>, <i>Lactobacillus</i>, <i>Bacillus</i>), while the condition with only 7.5 g COD.L⁻¹ of co-substrates and 7.6% vinasse favoured H₂ producers (<i>Clostridium</i>, <i>Thermoanaerobacterium</i>, <i>Pseudomonas</i>). These findings guide future feeding strategies to optimize bioproduct yield, favouring the generation of target bioproducts and ensuring a holistic view of vinasse and molasses utilization for fermentative H₂ biogas production.