The effects of various LED (light emitting diode) lighting strategies on simultaneous biogas upgrading and biogas slurry nutrient reduction by using of microalgae Chlorella sp.

• The microalgae biogas upgrading system used in this study is effective.
• Red light is the optimum light wavelength for microalgae growth and biogas upgrading.
• Only moderate light intensities are suitable for microalgae growth.
• The optimal lighting strategy is incremental light intensity strategy.
• CH4 concentration in upgraded biogas is 92.87 ± 4.10% under optimal lighting strategy.

Biogas is a promising renewable energy which has to be upgraded to meet the efficient combustion standard. The microalgae biogas upgrading system used in this study could effectively upgrade biogas and simultaneously reduce biogas slurry nutrient. Red light was the optimum light wavelength for microalgae growth, biogas upgrading, and biogas slurry nutrient reduction. Only moderate light intensities (i.e., 400, 600, 800, and 1000 μmol m−2 s−1) were suitable for microalgae growth. The optimal lighting strategy should be incremental light intensity strategy since it could avoid photoinhibition at the initial culture phase and insufficient light intensity at the latter culture phase. Under this lighting strategy, the microalgae dry weight was 446.98 ± 25.32 mg l−1; the methane concentration in the upgraded biogas was 92.87 ± 4.10%; the chemical oxygen demand, total nitrogen, and total phosphorus removal efficiency was 92.67 ± 5.14%, 80.87 ± 6.25%, and 79.33 ± 6.18%, respectively.