The impact of light intensity and wavelength on the performance of algal-bacterial culture treating domestic wastewater

Light is the main energy source for microalgae, and the intensity and wavelength of light influence cell metabolism and biomass composition, which, in turn, affects wastewater treatment. The objective of this study is to examine how different light intensities and light wavelengths affect the growth of mixed algal-bacterial culture while treating sewage. Three different light intensities (100, 200, and 300 μmol/m2-s) of four different light wavelengths (blue, red, white, and yellow) were selected for this study. The dissolved organic carbon (DOC), dissolved nitrogen (DN), and dissolved phosphorus (DP) in influent and effluent samples were measured, along with chlorophyll content in the biomass. The highest chlorophyll concentration of 3.5 mg/L was observed at 100 μmol/m2-s intensity of red light. The concentration of chlorophyll decreased as light intensity increased, with exception of white light. The highest DOC removal of 84% was observed at 300 μmol/m2-s intensity of blue light whereas the highest DN (51%) and DP (80%) removal was observed with a red light intensity of 100 μmol/m2-s. Overall, blue light with an intensity of 300 μmol/m2-s and red light with an intensity of 100 μmol/m2-s were found to be the most efficient at removing carbon and nutrients. The results suggested that the color and intensity of light influence algal-bacterial growth and wastewater treatment efficiency.