Influence of temperature on volatile fatty acid production and microbial community structure during anaerobic fermentation of microalgae

The objectives of this study were to investigate the effect of operating temperature on volatile fatty acids (VFAs) production from microalgal biomass, and to clarify the relationships between VFAs accumulation at different temperatures and the corresponding bacterial communities. The VFA yields were 0.10 +/- 0.017, 0.12 +/- 0.008, and 0.34 +/- 0.009 g/g VS at 35, 45, and 55 degrees C, respectively. The proportion of acetic acid decreased from 85.6% to 65.8% as operating temperature increased, whereas that of propionic acid increased from near 0% to 15.5% and that of iso-valeric acid remained relatively stable (10.2-11.2%). Bacterial communities at different operating temperatures consisted mostly of the phyla Proteobacteria, Bacteroidetes, and Firmicutes, which can degrade organic compounds effectively. Bacillus sp. was more predominant at 55 degrees C than at mesophilic temperatures, suggesting that this microorganism contributed significantly to the higher hydrolysis rate and VFA yield at this operating temperature. (C) 2015 Elsevier Ltd. All rights reserved.