Purified crude glycerol by acid treatment allows to improve lipid productivity by Yarrowia lipolytica SKY7
Graphical abstract
Introduction
Net energy production and carbon dioxide emission are the two most important factors for evaluating the sustainability of new energy sources. Biodiesel is a promising new energy source and is safe, renewable, non-toxic, and biodegradable. It is produced mainly from vegetable oils and animal fats [1]. The increasing price of edible oil and limited feedstock sources leads to unaffordable biodiesel production. Crops like rapeseed, jatropha, and canola are used for biodiesel production, but they have disadvantages such as, dependency on land and climatic conditions, removal of rain forest, high labour and energy intensive process [2]. The lipid, which is derived from microorganisms, also known as microbial oil, can be quickly synthesized and accumulated in cells; its fatty-acid composition is highly similar to that of vegetable oil [3,4]. However, cost assessment revealed that the unit production cost of microbial biodiesel produced using commercial substrate was estimated to be $5.9/kg biodiesel while market price of biodiesel is around $1/L [5]. Hence, renewable and cheap carbon sources are being explored for lipid production to reduce its production cost [[6], [7], [8]]. Therefore, crude glycerol has attained researchers’ attention in past years as it is a by-product of biodiesel industry and using crude glycerol for lipid production will help maintaining circular economy [9].
However, crude glycerol has several impurities depending on the trans-esterification process: catalyst, methanol, soap, free fatty acids, metals and salts [10,11]. The consideration for purification of glycerol is largely dependent on the usage of glycerol. Acidification is an effective technique for removal of soap, metals and salts from the crude glycerol [9,12,13]. Purified glycerol, thus obtained, can be used as a carbon source in fermentation process for lipid production. Thus, objective of this study was to purify crude glycerol with high potassium content and use it as a carbon source for microbial lipid and citric acid production using Yarrowia lipolytica SKY7 (YL). A comparison between purified and unpurified (or crude) glycerol was made in terms of specific growth rate, product productivity and product yield coefficient. Moreover, a mass balance was made for purification of 1 L of crude glycerol and chemicals cost involved in in the purification process has been discussed. This study provides a way for valorization of crude glycerol with high potassium content for microbial lipid production.
Section snippets
Crude glycerol purification
The crude glycerol was obtained from Canadian biodiesel producing company BIO-LIQ INC. BIOLIQ glycerol was high on potassium concentration as potassium methoxide was used as catalyst during trans-esterification. The crude glycerol contained potassium methoxide which is highly toxic compound as it is an alkoxide of methanol (strong base). For crude glycerol purification, phosphoric acid was added to crude glycerol (neutralization using pH adjustment to 2) followed by batch centrifugation at
Variation of biomass concentration
Variation of biomass concentration in the medium with pure, purified and crude glycerol as carbon source is highlighted in Fig. 1. It is clear that purified glycerol performed better than crude glycerol with biomass concentration of 51.67 g/L and 20.36 g/L, respectively at 96 h. Lower biomass in the medium with crude glycerol could be due to higher potassium concentration (4.8 g/L, Table 2) in the beginning of the process.
After adding feed in the medium with crude glycerol at 24 h, the
Conclusion
In this study, crude glycerol with high potassium concentration was purified by precipitating excess phosphorus as KH2PO4 with phosphoric acid. The purified glycerol thus obtained was employed as carbon source for lipid production using Y. lipolytica SKY7. At 96 h of fed-batch fermentation, the purified glycerol gave higher biomass (51.67 g/L) and lipid concentration (19.47 g/L) than crude glycerol (20.36 g/L and 7.21 g/L, respectively). The process performance of purified glycerol medium was
CRediT authorship contribution statement
Lalit R. Kumar: Conceptualization, Methodology, Formal analysis, Writing - original draft, Data curation. Sravan K. Yellapu: Investigation, Resources, Validation. R.D. Tyagi: Supervision, Funding acquisition, Project administration, Writing - review & editing. Patrick Drogui: Supervision.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors would like to acknowledge the Natural Sciences and Engineering Research Council of Canada (grant A4984 and Canada Research Chair) for financial support. We are grateful to the technical staffs of INRS-ETE (Mr. Stephane Moise and Mr. Stefane Premont) for their timely help to analyze the samples on LC–MS and ICP-MS. The authors acknowledge biodiesel producing company in Canada; BIO-LIQ INC for providing the crude glycerol for the research work.
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