Enhanced biomass and lipid production of Chlorella vulgaris through the utilization of municipal wastewater as a nutrient source: A sustainable feedstock for biodiesel production

Abstract

Municipal wastewater has high nutritional contents of nitrogen and phosphorus that are essential for microalgae growth. In order to reduce the cost of producing biodiesel, microalgae can be cultivated using municipal wastewater as a sustainable source of nutrients. The present investigation aimed to enhance the growth and lipid content of the newly isolated green microalga, Chlorella vulgaris by adjusting different culture conditions such as light intensity, temperature, pH, and supplementation of municipal wastewater. C. vulgaris was cultured in different combinations (75:25, 50:50, and 25:75) of municipal wastewater (WWC), diluted with Bold’s Basal Medium (BBM) and reverse osmosis (RO) water separately. In this experiment, about 75% of WWC diluted with 25% BBM supported the maximum production of biomass and lipids. From this experiment, the maximum production of biomass 15.6 g/L and the lipid 5.56 g/L were observed on the 12th day of cultivation. Further, the presence of functional groups was briefly examined in algae biomass samples by using Fourier transform infrared spectroscopy (FTIR). The nuclear magnetic resonance (NMR) method has been used to analyze the chemical composition of biodiesel. These results confirm the presence of alkyl group protons, methylene (CH₂) group protons, and aromatic protons. Further, the fatty acid methyl esters in biodiesel were confirmed by gas chromatography and mass spectrometry (GCMS) analysis. All these results showed the significant lipid composition extracted from the biomass of C. vulgaris cultivated in municipal wastewater for biodiesel production. Lastly, the properties of biodiesel were analyzed and compared with the standard of American Society Testing and Materials (ASTM). Furthermore, utilizing municipal wastewater as a sustainable nutrient source can significantly minimize the production costs thereby this strain can be considered a sustainable feedstock for biodiesel production.