Photosynthetic CO2 uptake by microalgae for biogas upgrading and simultaneously biogas slurry decontamination by using of microalgae photobioreactor under various light wavelengths, light intensities, and photoperiods

Anaerobic digestion not only produces raw biogas which needs to be upgraded, but also nutrient-rich waste stream biogas slurry which needs decontamination. Therefore, this research focused on the effects of various light wavelengths, light intensities, and photoperiods on biogas upgrading and simultaneously biogas slurry decontamination by using of microalgae photobioreactor. The microalgae photobioreactor was a transparent polyethylene bag (80 cm × 60 cm × 11 cm). The results demonstrated that biogas upgrading and simultaneously biogas slurry decontamination was successfully achieved by the use of the photosynthetic CO2 uptake by microalgae photobioreactor. The optimal light wavelength was the mixed LED red:blue = 5:5; whereas the optimized lighting control strategy was: low light intensity (300 μmol m−2 s−1) with long photoperiod (16 h light:8 h dark) for the time course of 0-48 h, moderate light intensity (600 μmol m−2 s−1) with middle photoperiod (14 h light:10 h dark) for the time course of 48-96 h, and high light intensity (900 μmol m−2 s−1) with short photoperiod (12 h light:12 h dark) for the time course of 96-144 h. Its biogas CO2 removal efficiency was 85.46 ± 6.25%. Its removal efficiency of chemical oxygen demand, total nitrogen, and total phosphorus were 85.23 ± 8.32%, 87.10 ± 7.55%, and 92.40 ± 3.05%, respectively.