Effects of various LED light wavelengths and intensities on the performance of purifying synthetic domestic sewage by microalgae at different influent C/N ratios

In Chinese rural areas, domestic sewage is one of the main sources of water pollution that may cause water eutrophication if directly discharged into natural waters without appropriate treatment. This study demonstrates that the microalgae Chlorella vulgaris can effectively remove nutrients from domestic sewage. In this process, red is the optimal light wavelength, with an intensity strategy as follows: Phase 1, 0–48 h with 1000 μmol m−2 s−1; Phase 2, 48–96 h with 1500 μmol m−2 s−1; Phase 3, 96–120 h with 2000 μmol m−2 s−1; and Phase 4, 120–144 h with 2500 μmol m−2 s−1. The optimal cultivation time was 144 h. Nutrient removal efficiency was significantly affected by the light wavelength, light intensity, the effect of the interaction between light wavelength and intensity, as well as the effect of the interaction among light wavelength, light intensity, and influent C/N ratio. Moreover, the total nitrogen and total phosphorus removal efficiencies were significantly affected by the influent C/N ratio. In this study, the optimal influent C/N ratio is 5:1.

► The optimal light wavelength for nutrient removal by Chlorella vulgaris was red. ► The 144 h was determined as the optimal cultivation time. ► The optimal influent C/N ration was determined as C/N ratio of 5:1. ► The nutrient removal was significantly affected by characteristics of light source. ► The nutrient removal efficiencies were significantly affected by influent C/N ratios.