The effect of varying LED light sources and influent carbon/nitrogen ratios on treatment of synthetic sanitary sewage using Chlorella vulgaris

Sanitary sewage can create serious environmental problems if discharged directly into natural waters without appropriate treatment. This study showed that red light is the optimum light wavelength for growing microalgae Chlorella vulgaris in microalgae biological wastewater treatment systems, given a harvest time of 144 h. Only moderate light intensities (1,000, 1,500, 2,000, and 2,500 μmol m^?2 s^?1) were able to remove nutrients from synthetic sanitary sewage, but higher light intensity led to better nutrient removal effects. Because of economic considerations, the optimum light intensity range for efficient nutrient removal was determined to be between 1,500 and 2,000 μmol m^?2 s^?1. Furthermore, nutrient removal efficiency was significantly affected by light wavelength, light intensity, the interaction of these two factors, and the interaction among light wavelength, light intensity, and influent carbon/nitrogen (C/N) ratios. Total nitrogen and total phosphorus removal efficiency was also significantly affected by influent C/N ratios. Appropriate control of carbon and nitrogen source concentrations enabled optimal nutrient removal. The optimal influent C/N ratio was determined to be 6:1.