A preliminary study of cost and energy analysis of bio-fuel production from microalgae cultivated in parboiled rice mill wastewater

Abstract

Microalgae industry is rapidly growing industry with high potential for value added products. Especially microalgae derived biofuels provide a sustainable solution for continuously rising energy crisis, food security and greenhouse gas emission. However, at present economical limitations make this green fuel not commercially viable. Integrating wastewater treatment with the microalgae cultivation can significantly reduce the biofuel production cost. Parboiled rice mill is rich in nutrients and capable of providing inexpensive water resources. Nevertheless, energy and cost analysis are required in order to ensure the cost effectiveness of such approaches. Thus, the study evaluates the cultivation of microalgae in rice mill wastewater in the outdoor uncontrolled conditions for the cost and energy effective, biofuel production. Microalgae biomass was cultivated in low-cost poly-bags of 3L volume using parboiled rice mill wastewater in outdoor. Cultivation was done under ambient temperature with 0.2vvm aeration without any optimization of the natural environmental conditions. This can be rationalized to reflect a realistic scenario in terms cost and energy estimation of production of lipid and bio-ethanol at laboratory scale. The obtained bioethanol and lipid yield were 1.4% and 5.81% respectively. Cultivation of the microalgae consumed 2.16 MJ of energy per gram. The required energy content for production of bioethanol and lipid from a gram of biomass were 3.61764 MJ and 3.5336 MJ respectively. Cost of microalgae cultivation to produce gram of bioethanol and lipid were $ 22.91 and $ 5.52 respectively. Total production cost per gram of bioethanol and lipid were $ 64.73 and $ 55.91 respectively. These values are comparatively exorbitant. Since the production was at very small scale and the yield was very low due to the microalgae cultivation in outdoor under natural condition in laboratory scale. The production of biofuel could become economically feasible if the yield could optimally increase and simultaneous production of bioethanol and lipid along with other value added products such as biofertilizer, aquaculture feed etc. could be achieved. Therefore, the method resulted in the lower cultivation cost can be incorporated with the residual biomass utilization and could produce sustainable microalgae biofuel.