Biological carbon capture from egg-washing wastewater using microalgae for sustainable biofuel production

Carbon capture, storage, and utilization are essential strategies for mitigating climate change. Biological carbon capture, particularly algae-based systems, offers a low-energy alternative to traditional chemical processes, which are energy and water-intensive. This study explored the cultivation of Chlorella vulgaris using egg-washing wastewater, with the harvested biomass utilized for oil extraction and subsequent biofuel production. The harvested biomass was subjected to oil extraction using solvents after applying four different pretreatment methods, including UV light exposure, moist heat, microwave treatment, and electrocoagulation. Although UV-C treatment yielded the highest lipid content, oil yields for; UV, moist heat, electrocoagulation, and microwave pretreatments were 20.8, 28.9, 37.5, and 25.0 %, respectively. Electrocoagulation pretreatment not only delivered the highest oil yield but also improved the fatty acid profile, significantly increasing the levels of methyl heptadecanoate (C17:0) and methyl heptadecanoate (C17:1). Compared to conventional crop-based biodiesel, algae biodiesel exhibits lower energy density. Still, it offers advantages such as improved oxidation stability, a higher cetane number, and reduced nitrogen oxide emissions due to its lower polyunsaturated lipid content and shorter carbon chain lengths. However, its performance at low temperatures remains composition-dependent. Overall, these findings demonstrate the potential of C. vulgaris cultivated in egg-washing wastewater for biodiesel production while indicating that electrocoagulation stands out as a sustainable alternative for large-scale applications with energy efficiency, improved oil composition, and faster processing time.