Anaerobic co-digestion of microalgal biomass, sugarcane vinasse, and residual glycerol from biodiesel using simplex-centroid mixture design: methane potential, synergic effect, and microbial diversity

Microalgal biomass (MB) is a promising feedstock for bioenergy production. Nonetheless, the cell recalcitrance and the low C/N ratio limit the methane yield during anaerobic digestion. As an alternative to overcome these challenges, MB co-digestion with different feedstocks has been proposed. Thus, this study evaluated the anaerobic co-digestion (AcoD) of MB cultivated in wastewater with sugarcane vinasse (VIN) and residual glycerol from biodiesel production (GLY). Batch tests were conducted using augmented simplex-centroid mixture design to investigate the impact of AcoD on methane production (SMP), synergistic effects, and the influence on microbial community. When compared to MB digestion, 150 NmL CH₄.g^-1VS, binary and ternary AcoD achieved SMP increases from 120 to 337%. The combination of 16.7:16.7:66.7 (MB:VIN:GLY) showed the highest SMP for a ternary mixture (631 NmL CH₄.g^-1VS). Optimal synergies ranged from 1.3 to 1.4 and were primarily found for the MB:GLY AcoD. Acetoclastic Methanosaeta genus was predominant, regardless the combination between substrates. Despite the largest SMP obtained from the MB:GLY AcoD, other ternary mixtures were also highly synergetic and therefore had strong potential as a strategic renewable energy source.