CO2 favors the lipid and biodiesel production of microalgal-bacterial granular sludge

Microalgal-bacterial granular sludge (MBGS) serves as an environmentally friendly wastewater treatment tech-nology with CO2 capture potential. Accordingly, this study intended to investigate the lipid and biodiesel pro-duction of MBGS with CO2 addition. The results showed that CO2 addition could increase not only the total lipid content in MBGS but also the biodiesel quality. The total lipid content in MBGS typically increased from 725.92 mg/L to 1056.55 mg/L with CO2 addition during the 30 days experiment. Furthermore, when CO2 was added, the C18:1 content of MBGS increased significantly from 0.17 (mu g/mg)center dot FW to 0.22 (mu g/mg)center dot FW, indicating that higher quality of biodiesel might be produced. Saturated fatty acid and polyunsaturated fatty acids contents of MBGS with CO2 addition were respectively 1.30 (mu g/mg)center dot FW and 0.13 (mu g/mg)center dot FW, while the monounsaturated fatty acids content of MBGS with CO2 addition was higher than without CO2 addition. This indicated that the MBGS system with CO2 addition appeared to be better suited for producing biodiesel. Microbial community further analysis revealed that CO2 addition might promote the growth of Chlorophyta, Cyanobacteria and Chloroflexi. This background information would aid in promoting the further application of MBGS for carbon capture and resource recovery towards carbon neutral or negative wastewater treatment.