Substrate degradation, biodiesel production, and microbial community of two electro-fermentation systems on treating oleaginous microalgae Nannochloropsis sp

[Display omitted] •Electro-fermentation system (EFS) was an effective way to treat Nannochloropsis sp.•Microbial electrolysis cell (MEC) performed better than microbial fuel cell (MFC).•MEC-EFS had better substrate degradation & electrochemical performance than MFC-EFS.•MEC-EFS & MFC-EFS improved lipid extraction and biodiesel nature by biohydrogenation.•Ruminococcus &Geobacter in anodic biofilm played key roles on MEC-EFS performance. Electro-fermentation system (EFS) emerges its effectiveness on treating microalgae for biodiesel production, but much is unknown about biodegradation behaviors, biodiesel characteristics, and microbial community. Compared with conventional fermentation system (CFS), microbial electrolysis cell-based EFS (MEC-EFS) and microbial fuel cell-based EFS (MFC-EFS) were investigated for the performance while treating microalgae Nannochloropsis sp. Results indicated that MEC-EFS presented much higher first-order decomposition rate coefficients of carbohydrates and proteins (1.212/d and 0.951/d) than those of CFS (0.615/d and 0.794/d) and MFC-EFS (0.518/d and 0.415/d). Compared with MFC-EFS, MEC-EFS showed better electrochemical performance (2.17 A/m3vs. 0.95 A/m3). Moreover, MEC-EFS reached the highest extracted lipid to biomass ratio (43.3%), followed by MFC-EFS (32.3%) and CFS (27.7%). By strengthened microbial biohydrogenation, MEC-EFS and MFC-EFS had higher saturated fatty acids ratio (78.8% and 70.6%) than that of CFS (56.1%). For MEC-EFS, enriched Ruminococcus and Geobacter in anodic biofilm might contribute to favorable biohydrogenation and electrochemical performance.