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.