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

Abstract

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, 0–48h with 1000μmolm−2s−1; Phase 2, 48–96h with 1500μmolm−2s−1; Phase 3, 96–120h with 2000μmolm−2s−1; and Phase 4, 120–144h with 2500μmolm−2s−1. The optimal cultivation time was 144h. 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.