Integrating nutrient recovery from wastewater and <scp>CO</scp> ₂ capture by <i>Chlorella vulgaris</i> microalgae under mixotrophic conditions for biofuel production

Abstract The massive production of palm oil mill effluent (POME) demonstrated the huge potential of nutrient resources recovery through the circular economy for sustainable utilization purposes. The increase in carbon dioxide (CO 2 ) emissions due to fossil fuel combustion has drawn global attention to CO 2 emission mitigation. Microalgae are well‐known for their ability to absorb CO 2 , recover nutrients from wastewater, and produce biofuel. However, due to the complex metabolism between the autotrophic and heterotrophic processes, the CO 2 uptake performance of microalgae cultivated in wastewater under mixotrophic conditions must be investigated. In this study, microalgae Chlorella vulgaris were cultivated in a medium consisting of 20 L, 5 vol% POME‐nourished medium, with exposure to light and continuous aeration. The nutrient removal efficiencies for chemical oxygen demand (COD), ammonia, phosphorus, nitrate, and nitrite are 70%, 100%, 43%, 55%, and 52% respectively at the 7th day. The duration of 7 days is sufficient as the optimal CO 2 uptake was achieved on the 7th day. The microalgae biomass contains around 12 wt% of lipid content with a heating value of 19,850 kJ/kg, which is comparable to wood, thus emphasizing the biofuel potential. This study demonstrated the feasibility of integrating wastewater treatment and CO 2 sequestration by microalgae for biofuel production.