## CH amounts v v produced

CO2 removal rate (%) and CH4 amount (v/v) were investigated as a function of operating time to evaluate differences in biogas upgrade with varying mixed wavelengths ratio for the three microalgal strains (Fig. 4a–c). During the experiment, CO2 amount (v/v) decreased as CH4 amount (v/v) increased. In all mixing conditions with red and blue light for S. obliquus, the CO2 removal rate (%) was approximately 49.95%–62.31%, which is slightly higher than that Deltorphin II for C. vulgaris (43.21%–55.39%) and N. oleoabundans (40.25%–54.39%). No significant differences in biogas CO2 REs among the three microalgal strains, (P > 0.05) were found at red:blue ratios of 5:5 and 7:3 but their corresponding REs were significantly higher (P < 0.05) than those at red:blue ratios of 9:1 and 1:9. Therefore, CO2 RE can be increased during photosynthesis in photoautotrophic microalgal cultures by supplying mixed wavelengths of red:blue = 5:5 and 7:3 ( Oilgae, 2010).