Combining fermentation broth with spent water recycling for microalgae cultivation: nutrient reutilization, biodiesel production and techno-economic simulation

This study presents an innovative and promising technology, Water Cycling Combined Fermentation Broth (WC²FB), which offers a sustainable solution to significantly reduce the costs associated with microalgae-based biodiesel production. The innovative approach involves utilising food waste as a nutrient source, supplemented by recycled water after microalgae harvesting, with the goal of improving the viability of industrial biofuel production. The results of nutrient removal efficiency demonstrated that the addition of 15% fermentation broth to the microalgal suspension efficiently utilised volatile fatty acids, resulting in a significant increase in lipid content. Additionally, biocomponent analysis confirmed that the WC²FB mode did not compromise the desirable properties of biodiesel. Through techno-economic simulations, we predicted a 90% probability of achieving net present value (NPV) at a selling price of $5/kg. Finally, we recommended that directing future efforts be directly towards the development of culture devices, low-cost bioflocculation methods, and biorefinery extraction to further advance biodiesel production.