Cultivation of microalgae for biofuel production: coupling with sugarcane-processing factories

Abstract Background Despite their potential as biofuel resources, large-scale production of biofuels from microalgae is still uncertain primarily due to a lack of feasibility of the process and that it proves to be capital and energy intensive. Therefore, an integration of microalgal cultivation with other processes for achieving an inexpensive nutrient and energy use is an important issue. In the present study, the potential of the flue gas and the wastewater of a sugar factory to support microalgae growth for biofuel and bio-fertilizer production is evaluated. Methods The study was carried out by following a case study approach; an Ethiopian sugarcane-processing factory, Metahara sugar and ethanol production factory, was selected for this purpose. Conceptual microalgal biofuel production was integrated with the real sugarcane-processing factory, and the process was evaluated with regard to the product outputs and energy requirements. Results The integrated process model shows that three products, biodiesel, upgraded biogas, and bio-fertilizer with production capacities of 188 tons/year, 1,974,882 m 3 /year and 42 tons/year, respectively, were produced. For the production of these products, the electricity and thermal energy demand of the integrated process amounted to 1822.13 and 3244.99 MWh/year, respectively. A sensitivity analysis shows that the oil content of the algae, the nitrogen content of the waste, the oil extraction efficiency, and the transesterification efficiency are the main factors which affect the biodiesel production capacity of the integrated process. Conclusions This case study approach investigated the potential of a future possible bio-refinery and environmental pollution reduction concept by integrating microalgae biomass production with sugarcane-processing factory wastes and by-products. It was found that the factory wastes and by-products have a significant potential for a viable biofuel production from microalgae.