Fig. 2

Biogas and methane productivity via anaerobic fermentation of algal biomass in continuous mode. The biogas productivity was monitored online and methane content was measured weekly (left = replete-N BM, right = low-N BM). Organic loading rate (OLR) is indicated by shades of gray in the background, thereby following biomass concentrations were applied: OLR1 = 1 g VS L⁻¹ day⁻¹, OLR2 = 2 g VS L⁻¹ day⁻¹, OLR4 = 4 g VS L⁻¹ day⁻¹. Error bars represent mean productivity of previous 7 days (SE, n = 7). N nitrogen, BM biomass, VS volatile solids