Comparative Treatment Efficiency and Fatty Acid Synthesis of Chlorella vulgaris: Immobilization Versus Co-cultivation

Abstract

Microalgae consists a promising feedstock for biofuel production due to their high growth rates and lipid content. Microalgal wastewater remediation can achieve both organic matters removal and biodiesel production, leading to economic benefits. In this study, immobilized microalgae and algae-bacteria consortia were used to treat synthetic fracturing wastewater. Organic matter removal, biomass production and lipid synthesis by co-culture of Chlorella vulgaris and Bacillus bacteria were investigated in comparison with an algae immobilization system during the process. The chemical oxygen demand removal rate and lipid concentration of the co-culture were both lower than those of the immobilized C. vulgaris, while algal biomass under the two cultivation conditions was similar. The immobilized algae provided higher amount of fatty acids, especially mono-unsaturated fatty acids, than the algae-bacteria consortia. Most of the fuel properties of biodiesel produced in both immobilized and co-cultured C. vulgaris complied with the specifications for standard biodiesel. The comparative results of enzyme activity showed that immobilization can enhance the activity of acetyl-CoA carboxylase, the key enzyme for fatty acids synthesis, leading to the formation of more fatty acids and lipids. Furthermore, immobilization decreased the ADP-glucose pyrophosphorylase activity and inhibited starch formation. Immobilization favors lipid production and removal of organics by C. vulgaris.