Acidogenic fermentation of Scenedesmus sp.-AMDD: comparison of volatile fatty acids yields between mesophilic and thermophilic conditions

This study compared the acidogenic fermentation of Scenedesmus sp.-AMDD at laboratory-scale, under mesophilic (35 °C) and thermophilic conditions (55 °C). Preliminary batch tests were performed to evaluate best conditions for volatile fatty acid (VFA) production from microalgal biomass, with respect to the inoculum, pH and nutrients. The use of bovine manure as inoculum, the operating pH of 4.5 and the addition of a nutrient mix, resulted in a high VFA production of up to 222 mg g-1 total volatile solid (TVS), with a butyrate share of 27%. Both digesters displayed similar hydrolytic activity with 0.38±0.02 and 0.42±0.03 g soluble chemical oxygen demand (COD) g-1 TVS for the digesters operated at 35 and 55 °C, respectively. Mesophilic conditions were more favourable for VFA production, which reached 171±5, compared to 88±12 mg soluble COD g-1 TVS added under thermophilic conditions (94% more). It was shown that in both digesters, butyrate was the predominant VFA.