New insights into efficient lipid production and decolorization of Congo red by microalgae under anaerobic environment: Performance and degradation mechanisms

Dye wastewater is a type of wastewater that is difficult to treat, and the degradation of dye using microalgae is both effective and profitable. This study cultivated microalgae Asterarcys quadricellulare R-56 under anaerobic condition for the removal of Congo red dye and explored the growth and lipid accumulation of microalgae with only Congo red dye as the carbon source, and a pathway for the degradation of Congo red by microalgae was proposed. The removal efficiency of Congo red (60 mg/L) by microalgae under light anaerobic culture mode reached 91.6 %, which was higher than that of light aerobic condition (60.8 %). The highest microalgae biomass was 406.4 ± 18.3 mg/L with a concentration of Congo red of 100 mg/L, which was 1.6 times of the control group. Moreover, the highest lipid production and lipid content were 187 ± 3.2 mg/L and 61.1 ± 3.1 %, respectively. In addition, the total saturated and monounsaturated fatty acid content of microalgae lipids reached 96.7 % at 100 mg/L Congo red, which was higher than that of the control group (85.5 %), more favorable for the production of high-quality biodiesel. The mechanism of removing Congo red by microalgae was mainly the biosorption and biodegradation. This study shows that the use of microalgae for dye purification and resource recovery is a promising strategy.