Purified crude glycerol by acid treatment allows to improve lipid productivity by Yarrowia lipolytica SKY7

doi:10.1016/j.procbio.2020.06.010

Process Biochemistry

Volume 96, September 2020, Pages 165-173

https://doi.org/10.1016/j.procbio.2020.06.010 Get rights and content

Highlights

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Crude glycerol (with high potassium concentration) was purified and used for lipid production.
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Purified glycerol resulted in higher lipid and biomass productivity.
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Lipid yield on purified and pure glycerol as substrate was comparable.
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Potassium salt with high economic value was produced during purification.

Abstract

In this study, crude glycerol with high potassium concentration was purified using acid treatment and used as carbon source for lipid production using Yarrowia lipolytica SKY7. The crude glycerol was purified using phosphoric acid (pH 2) followed by centrifugation. When purified glycerol was used as carbon source for fermentation, higher biomass productivity (0.54 g/L/h) and lipid productivity (0.2 g/L/h) was observed at 96 h compared to crude glycerol. Results indicated that 6.32 g/L potassium in crude glycerol medium was inhibitory for cell growth and lipid production by Y. lipolytica. Yield coefficients, productivities and specific growth rates were calculated for each glycerol medium. The process performance with purified glycerol medium was comparable to that of pure glycerol medium. A higher lipid yield was obtained in purified glycerol medium (0.21 g/g glycerol) than crude glycerol medium (0.124 g/g glycerol). During purification of crude glycerol, KH₂PO₄ was also produced as by-product. This study provides a way for valorization of crude glycerol with high potassium concentration for microbial lipid production.

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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Purified crude glycerol by acid treatment allows to improve lipid productivity by Yarrowia lipolytica SKY7

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Crude glycerol purification

Variation of biomass concentration

Conclusion

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgements

Fuel

Bioresour. Technol.

Process. Biochem.

Biochem. Eng. J.

Fuel Process. Technol.

Bioresour. Technol.

Bioresour. Technol.

Bioresour. Technol.

Renew. Sustain. Energy Rev.

Renew. Sustain. Energy Rev.

Waste Manag.

Fuel

J. Biosci. Bioeng.

J. Dairy Sci.

Trends Biotechnol.

Bioresour. Technol.