Performance of three microalgal strains in biogas slurry purification and biogas upgrade in response to various mixed light-emitting diode light wavelengths

The three microalgal strains were cultivated, namely, Chlorella vulgaris, Scenedesmus obliquus, and Neochloris oleoabundans, by applying mixed light-emitting diode wavelength treatments to biogas slurry in a photobioreactor bag. This study aims to compare the growth and nutrient removal efficiency of the algae and determine their roles for biogas upgrading. At red:blue = 5:5, S. obliquus and C. vulgaris efficiently removed COD and TP, respectively. S. obliquus demonstrated high N removal efficiency at red:blue = 7:3. The same strain significantly improved removal capacity for all nutrients compared with C. vulgaris and N. oleoabundans, particularly at red:blue = 5:5, 7:3, and 3:7. For biogas upgrade, CH4 contents were higher than 75% (v/v) for all strains. The algae exhibited particularly good CH4 enrichment at red:blue = 7:3, 5:5. Results show that microalgal biomass production offers real opportunities for addressing issues, such as nutrient reduction, CO2 removal, and biogas enrichment.