Cultivating microalgae using municipal wastewater can achieve not only treatment of the wastewater but also recovery of algae for use as a biofuel energy source. Wastewater provides necessary nutrients, such as nitrogen and phosphorus, and water for microalgal growth. Because of the complexity of components of municipal wastewater, variety of adaptability, and tolerance to wastewater of different microalgal species, it is necessary to select a suitable microalgal species with high performance in lipid production and identify proper pretreatment of the wastewater to achieve high lipid production using municipal wastewater for algal biofuel production. Based on microalgal growth, lipid production, and clean-up performance of wastewater, we selected Scenedesmus obliquus wild strain and Chlorella pyrenoidosa mutant by ion beam implantation from a test group for the biofuel production. Laboratory test results showed that S. obliquus wild strain and C. pyrenoidosa mutant had respective lipid productions of 0.43 g·L-1 and 0.33 g·L-1, with more C16-C18 fatty acids, which were suitable for biodiesel production. The pollutant removals from the wastewater by S. obliquus wild strain and C. pyrenoidosa mutant were COD, 86.4% vs. 81.8%; NH4+-N, 100.0% vs. 100.0%; TN, 94.3% vs. 94.9%; and TP, 93.4% vs. 94.2% respectively. The two different microalgal strains required different pretreatments. After removal of large particles, the raw wastewater could be directly used for the cultivation of S. obliquus wild strain. To grow C. pyrenoidosa mutant with municipal wastewater, pretreatment procedures including precipitation followed by filtration should be employed.
Keywords: cultivation; lipids; microalgae; municipal wastewater; pretreatment.