Insights into volatile fatty acid production and fermentation pathways of microalgae biomass combined with vinasse and glycerol

: The fermentation of industrial wastes derived from water recovery (pretreated microalgae biomass, PTMB), biodiesel (glycerol, GLY), and ethanol (vinasse, VIN)) is a promising sustainable alternative for producing volatile fatty acids (VFA). In this study, controlled fermentation experiments were performed using PTMB-VIN and PTMB-GLY mixtures with varying substrate concentrations and retention times to optimize the VFA yield and production efficiency. Acid fermentation was optimized at a 3-day hydraulic retention time, and methanogenic reactions were enhanced at longer hydraulic retention times. Increasing the organic loading rate resulted in a high VFA yield (13.10 g VFA-COD. L-1) and a conversion rate of approximately 40%. GLY fermentation followed the oxidative and reductive pathways at a balanced redox potential. PTMB is linked to the oxidative pathway, and GLY is involved in the reductive pathway. Tests with PTMB-GLY resulted in limiting conditions, but significant observations regarding the metabolic pathway and the effect of PTMB were made.