Comprehensive study on volatile fatty acid production from Ettlia sp. residue with molecular analysis of the microbial community

The conversion of lipid extracted microalgal residues (LEμARs) into renewable energy provides a promising route for microalgal biodiesel production for various industries. In this study, volatile fatty acid (VFA) production and soluble chemical oxygen demand (SCOD) from the LEμAR of the green algae Ettlia sp. was optimized with the response surface methodology (RSM) varying the temperature from 25 to 65 °C and the food to microorganism ratio (F/M ratio) from 0.5 to 2.5 as the independent variables. A F/M ratio of 1.76 (g COD/g VSS) and temperature of 47.97 °C was found to be the optimal condition. Though the fit was rather lacking, the p-value was sufficiently significant at 1% α level validating the optimization model. Additionally, next generation sequencing (NGS) indicated significant correlations between VFA and its microbial community, revealing that an anaerobic bacterium species, Sporanaerobacter acetigenes, was a dominant VFA producer. This study shows that VFA production could indeed be a viable direction that would make the microalgae-based biofuel production competitive.