Mixotrophic cultivation of Chlorella vulgaris and its potential application for the oil accumulation from non-sugar materials Tamarys Heredia-Arroyo a , Wei Wei b , Roger Ruan c , Bo Hu c, * a Department of Chemical Engineering, University of Puerto Rico at Mayagu ¨ez, USA b Center for Learning Innovation, University of Minnesota at Rochester, USA c Department of Bioproducts and Biosystems Engineering, University of Minnesota at Twin Cities, 316 BAE, 1390 Eckles Ave, Saint Paul, MN 55108-6005, USA article info Article history: Received 16 August 2010 Received in revised form 16 February 2011 Accepted 18 February 2011 Available online 12 March 2011 Keywords: Chlorella vulgaris Microbial oil accumulation Glycerol Acetate as carbon sources Mixotrophic cultivation abstract Microbial lipid accumulation to provide alternative oil resources is an exciting research area, obtaining increasing attentions recently for the biodiesel production due to its high production efficiency and less demand of agricultural land. The aim of this study is to optimize the lipid accumulation of Chlorella vulgaris by using various carbon sources in heterotrophic and mixotrophic cultures. Different cultivation factors were studied on their influences to the cell growth and oil accumulation. Our results revealed that C. vulgaris could grow on autotrophic, mixotrophic and heterotrophic modes; and the mixotrophic cultivation especially could produce more cell biomass than the autotrophic or heterotrophic cultures individually or combined. The substrate concentration significantly influenced the final cell yield of the mixotrophic cultivations while the cell lipid content remained relatively constant. Glycerol was inhibitive to the cell growth while the microalgae strain could actively utilize acetate as the carbon source. This provides a promising niche in reducing the overall cost of biofuel production since this substrate can be obtained from some waste processes such as anaerobic digestion. ª 2011 Elsevier Ltd. All rights reserved. 1. Introduction Crude oil price has been dramatically fluctuating lately, causing serious negative impacts on the global and national economy. Massive consumptions of fossil fuels lead to serious concerns over global warming caused by greenhouse gases. Biofuel production offers an alternative to fossil fuels. It brings several benefits such as alleviation from foreign oil depen- dence, carbon neutral process; and it also brings profits to local farmers. Plant oil derivatives (especially soybean) provide an effective approach for alternative biofuel produc- tion. The typical product is biodiesel, the alkyl esters of fatty acid, obtained by transesterification of lipid with methanol or ethanol [1]. It can be used in pure form (B100) or may be blended with fossil diesel at any rate. The commonly used biodiesel is B99 because 1% of fossil fuel is applied to inhibit the mold growth, the main reason for a shorter shelf life. Biodiesel is around 5e8% less efficient than conventional fossil diesel, other than that, its application actually brings beneficial to the environment (except the NO x emission). Plant oil based biodiesel has gained some industrial success to replace fossil diesel; however, significant issues are hindering further development of this industry. First of all, there is a limit on the amount of feedstock oil that is available. Second, mass production of oilseed crop is raising environmental concerns. * Corresponding author. Tel.: þ1 612 625 4215; fax: þ1 612 624 3005. E-mail address: bhu@umn.edu (B. Hu). Available at www.sciencedirect.com http://www.elsevier.com/locate/biombioe biomass and bioenergy 35 (2011) 2245 e2253 0961-9534/$ e see front matter ª 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2011.02.036