Nutrients and COD removal of swine wastewater with an isolated microalgal strain Neochloris aquatica CL-M1 accumulating high carbohydrate content used for biobutanol production

In this study, a carbohydrate-rich microalga Neochloris aquatica CL-M1 was adapted to grow in swine wastewater. The effects of cultivation conditions (i.e., temperature, light intensity or N/P ratio) on COD/nutrients removal and carbohydrate-rich biomass production were investigated. The results indicate that the highest COD removal (81.7%) and NH₃-N removal (96.2%) was achieved at 150 µmol m⁻² s⁻¹ light intensity, 25 °C and N/P ratio = 1.5/1. The highest biomass concentration and carbohydrate content was 6.10 g L⁻¹ and 50.46%, respectively, when N/P ratio = 5/1. The resulting carbohydrate-rich microalgal biomass was pretreated and used as a feedstock for butanol fermentation. With the initial sugar concentration of 48.7 g L⁻¹ glucose and 3.4 g L⁻¹ xylose in the pretreated biomass, the butanol concentration, yield, and productivity were 12.0 g L⁻¹, 0.60 mol mol⁻¹ sugar, and 0.89 g L⁻¹ h⁻¹, respectively, indicating the high potential of using Neochloris aquatica CL-M1 for butanol fermentation.