Performance of mixed LED light wavelengths on biogas upgrade and biogas fluid removal by microalga Chlorella sp.

Chlorella sp. is a microalga that could be utilized effectively in the simultaneous biogas upgrade and biogas fluid nutrient removal. Mixed light-emitting diode (LED) light wavelength treatments (red:blue = 1:9, 3:7, 5:5, 7:3, and 9:1) were more appropriate for microalgal growth than monochrome LED light wavelength treatments (monochrome red, blue, and white). The most appropriate mixture ratios for biogas upgrade were red:blue = 7:3 and red:blue = 5:5. For biogas fluid nutrient removal, the most appropriate mixture ratio was red:blue = 5:5. Therefore, the optimal mixture ratio of LED light wavelengths was red:blue = 5:5. Under this treatment, components of upgraded biogas content (v/v) were 93.68 ± 3.25% CH4, 1.57 ± 0.42% CO2, 0.99 ± 0.06% O2, and 3.80 ± 0.34% H2O. The highest biogas fluid removal efficiencies of chemical oxygen demand, total nitrogen, and total phosphorus reduction were 78.91 ± 2.75%, 73.05 ± 2.04%, and 67.54 ± 1.46%, respectively.