Bioconversion of crude glycerol to microbial lipid using a robust oleaginous yeast Rhodosporidium toruloides ATCC 10788 capable of growing in the presence of impurities Bijaya K. Uprety, Sai Swaroop Dalli, Sudip K. Rakshit ⇑ Department of Chemical Engineering, Lakehead University, Ontario, Canada article info Article history: Received 10 November 2016 Received in revised form 8 December 2016 Accepted 25 December 2016 Keywords: Crude biodiesel glycerol Rhodosporidium toruloides ATCC 10788 Microbial lipid Growth on impurities Integration into biodiesel plant abstract In this work, crude glycerol, a by-product from a biodiesel industry was characterized and converted to microbial lipid. The sample of crude glycerol was found to contain 44.56 wt.% glycerol, 13.86 wt.% metha- nol, 10.74 wt.% of ash and 32.97 wt.% of soap. Rhodosporidium toruloides ATCC 10788 was studied for the first time to determine its ability to grow on crude glycerol as a carbon source. Methanol concentration as low as 0.5% (w/v) in the medium containing pure glycerol inhibited biomass and lipid production by this strain. However, higher concentration of methanol (i.e. 1.5% w/v) in crude glycerol containing media did not have the same effect on the organism, with double the biomass (21.16 g/L), triple the lipid concen- tration (11.27 g/L) and high lipid content (53.28 wt.%) produced at the end of 168 h. Unlike many other oleaginous microorganisms, the ability of this yeast to consume other impurities present in crude glyc- erol enhanced the growth and lipid production in such a way that the effect of methanol was masked or became insignificant. The lipid obtained contained 47.16% of oleic acid (a monounsaturated fatty acid), making it a very good feedstock for some oleochemical industries and the production of biodiesel. This bioconversion process which involves the production of lipid from crude glycerol waste stream will be of great interest to the biodiesel industry as it can be easily integrated into the existing biodiesel produc- tion plant. The use of such robust strains to produce other value added products can also be explored. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Fluctuating prices of fossil based diesel, depletion of its sources, environmental issues and increasing energy demand make biodie- sel an important alternative renewable source of energy [1–3]. Most developed countries have encouraged its use by implement- ing policies which mandate its blending (generally between 2 and 20% v/v) with fossil based diesel [4,5]. As a result, production of biodiesel has increased substantially across the world in the last decade [6]. However, biodiesel is still costlier than its fossil based counterpart and this constraint has to be addressed in order to make it more economically acceptable [1,7]. Another issue related to the use of biofuels like biodiesel is that arable land is used to grow the required oil crops. This has been perceived as a threat to food security leading to ‘‘food vs fuel” debates [8,9]. At present, the majority of biodiesel industries utilize vegetable based oils such as canola, rapeseed, and corn. These feedstocks are costly and contribute to approximately 70–85% of the overall biodiesel production process [10,11]. Cheaper feedstocks for biodiesel pro- duction can bring down the overall cost of production and make it competitive to fossil based diesel. Ideally, the alternate feedstock should not compete with food crops used at present [7,11,12]. Utilization of single cell oil (SCO) or microbial lipid as a non- food feedstock for biodiesel industries has gained importance in recent times as its chemical component is similar to vegetable based oils used for biodiesel production [13–17]. Various microor- ganisms (algae, yeast and fungi) are capable of accumulating lipids to levels more than 20% (w/w) of their biomass. Such microbes are called oleaginous microorganisms and the lipids they produce are known as single cell oils or microbial lipids [11,18,19]. Use of microbial lipids for biodiesel production has many advantages over plant based oils since their production life-cycles are short, they do not require the utilization of large land areas for their production, are unaffected by climatic condition and require comparatively less manpower [6,14,20]. However, techno-economic evaluations of such processes (i.e. biodiesel from single cell oil) show that this production route also depends on the cost of feedstock. The use of cheap feedstocks to produce such oil is thus very important to make the processes economically feasible [18,19]. http://dx.doi.org/10.1016/j.enconman.2016.12.071 0196-8904/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: srakshit@lakeheadu.ca (S.K. Rakshit). Energy Conversion and Management 135 (2017) 117–128 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman