Effects of nutrient composition, lighting conditions, and metal ions on the growth and lipid yield of the high-lipid-yielding microalgae (Chlorella pyrenoidosa) cultivated in municipal wastewater

Microalgae have attracted wide attention as an alternative raw material for bioenergy. Micmalgae cultivated in wastewater can reduce cultivation costs, and wastewater can be treated while the micmalgal biomass accumulates. Here, the effects of nutrient composition, lighting conditions, and metal ions on the growth and lipid yield of Chlorella pyrenoidosa cultivated in synthetic wastewater and actual wastewater were investigated. The microalgae treated with NO3--N showed the best growth status, and microalgae treated with NH4+-N exhibited the highest lipid yield. The maximum lipid yield was 0.18 g/L at a total phosphorus concentration of 5 mg/L. The maximum lipid content of C. pyrenoidosa was obtained at 4000 lux and 9:15 h L/D. In the metal ion experiment, the dry weight and total lipid yield in microalgae were highest when the Fe3+ concentration was 28.8 x 10(-3) mM, and the total lipid yield reached the maximum (0.25 g/L) when the Mg2+ concentration was 0.5 mM. The seven factors involved in C. pyrenoidosa cultivation were optimised using a uniform-design experiment. According to the model, the optimal culture conditions were as follows: photoperiodicity, 23:1 h L/D; ammonia nitrogen, 125 mg/L; Fe3+, 0 mM; light intensity, 9000 lux; phosphorus, 14 mg/L; Mg2+, 0.18 mM; and CO2, 1.3 vol%; furthermore, the maximum theoretical lipid yield was 0.31 g/L. Analysis of the fatty acid composition revealed a similar composition in both real and synthetic wastewater.