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 sugarcaneprocessing 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.

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One approach for the viable production of algal biomass is to couple its production with wastewater treatment plants, power and/or industrial plants. This is intended towards the utilization of the nutrients and the CO2 in the wastewater and in the flue gases of the industry respectively by the microalgae during their growth. In the present study microalgal biomass production was conceptually coupled with a sugar factory. The potential of the wastewater and the flue gas of the factory to support the growth of the microalgae was evaluated. Likewise the possible reduction of pollution by the microalgae was studied. The outputs from the coupled process were determined using the material and energy balance approach with a spread sheet. The cultivation model shows that 12 mg of total nitrogen (TN) and 7.4 mg of total phosphorus (TP) per liter of wastewater could be transferred to the algal growth ponds. It was found that there is a nitrogen deficit in the wastewater. With the supply of makeup nutrient, 120.5 tons/year microalgal biomass could be produced from the coupled process. Application of the assumptions resulted in the reduction of chemical oxygen demand (COD) (mg O2/L) from 2200 to 447, biological oxygen demand (BOD5) (mg O2/L) from 1200 to 207, TN (mg/L) from 15 to 0.6 and, TP (mg/L) from 10 to 1.5 in the wastewater. Integration of the sugarcane processing factories with algal biomass production is important for both biomass production and bioremediation.