Improved Chlorella vulgaris biomass production and nutrient removal from dairy wastewater by using light-emitting diodes and melatonin

The present study evaluated the effects of melatonin and light wavelengths on the growth rate of Chlorella vulgaris and on increasing nutrient removal from dairy wastewater. The microalgae were cultured under red, blue, green and white light emitting diodes (LEDs) with different concentrations of melatonin in dairy wastewater for 18 days. In melatonin-free samples, the maximum dry weight and cell number were observed under red, blue, green, and white LEDs, respectively. All concentrations of melatonin except 500 mu M in the wavelengths used caused a significant increase in dry weight and cell number compared to samples under the same wavelength without melatonin. The greatest amount of dry weight and cell number was observed in the microalgae treated with 10 mu M melatonin under red light LED. The use of red LED and 10 mu M melatonin increased dry weight and cell number by about 200% compared with samples grown under white light. Nitrate, phosphate and sulfate removal were 92%, 85% and 80%, respectively, under red LED and 10 mu M melatonin. These values were 3.02, 2.83, and 2.68 times higher, respectively, than samples grown under white light. Among all treatments, the maximum decrease in COD (80.6%) and BOD (88.65%) removal was observed with red LED and 10 mu M melatonin. Moreover, the greatest effect of melatonin in increasing TOC removal was observed with red LED (71.03%). The results show that the use of red LEDs and melatonin significantly increased the growth of C. vulgaris in dairy wastewater, thus improving the wastewater treatment parameters.