Abstract
To minimize the cost of biodiesel production, massively available biomass, rice straw was selected as starting material for fermentation by oleaginous yeast, Lipomyces starkeyi. Acid hydrolysis was carried out to obtain Rice Straw Hydrolysates (RSH). Maximum amount of glucose was liberated with 3.5% H2SO4. Highest levels of biomass (~12 g/L) and lipid content (~36%) of L. starkeyi were obtained through fermentation of RSH produced with 3.5% H2SO4. The optimum pH for biomass yield and lipid accumulation of L. starkeyi was 6.0. Periodic supplementation of fresh RSH increased lipid content and lipid yield approximately15% and 40%, respectively. The growth and lipid accumulation of L. starkeyi were enhanced when carbon and nitrogen sources were supplemented with RSH. Gas chromatographic analysis revealed that the lipid obtained from L. starkeyi cultivated with RSH was composed of saturated and unsaturated fatty acids. The fatty acid composition of this microbial lipid is similar to that of vegetable oils. The results reported herein indicate that rice straw might be a valuable alternative feedstock for microbial lipids production by L. starkeyi for biodiesel synthesis.
Highlights
Due to limited supply, exhaustion in the foreseeable future and negative environmental impacts of fossil fuel, biodiesel has attracted the attention lately as reliable alternatives
Hydrolysis was conducted with 10%, 5%, 3.5% and 0.0% (w/v) of H2SO4 to optimize the condition at which maximum amount of rice straw was transformed into fermentable sugars
Hydrolysis was performed with concentrations of H2SO4 lower than 3.5% and 3.5% of H2SO4 was the optimum one that liberated maximum level of glucose
Summary
Exhaustion in the foreseeable future and negative environmental impacts of fossil fuel, biodiesel has attracted the attention lately as reliable alternatives. As a matter of facts, biodiesel is a nontoxic, degradable and clean energy that can be obtained from a wide range of renewable sources. Usage of biodiesel reduces greenhouse gas emission, deforestation and pollution, and let a balance to be sought between agriculture, economic development and the environment [1]. It is reported that biodiesel produced from soy oil and waste grease can reduce the emission of greenhouse gas by 57% and 87%, respectively when compared to petroleum diesel [2]. Demand for biodiesel has increased significantly due to the instability of petroleum prices and the development of government measures in many countries around the world that a minimum proportion of biodiesel must be used in parallel of petroleum diesel. The high cost of biodiesel, of which raw material amounts to about 75%, has become one of the major obstacles to its wide application [3]
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