Microalgal triacylglycerides production in outdoor batch-operated tubular PBRs.

Giulia Benvenuti,Fang Ji,Packo P Lamers,Rouke Bosma,Anne J Klok,Maria J Barbosa,René H Wijffels

doi:10.1186/s13068-015-0283-2

Abstract

BackgroundMicroalgal triacylglycerides (TAGs) are a promising sustainable feedstock for the biofuel, chemical and food industry. However, industrial production of microalgal products for commodity markets is not yet economically viable, largely because of low microalgal productivity. The latter is strictly dependent on initial-biomass-specific (IBS) light availability (i.e. ratio of light impinging on reactor ground area divided by initial biomass concentration per ground area). This study investigates the effect of IBS-light availability on batch TAG production for Nannochloropsis sp. cultivated in two outdoor tubular reactors (i.e. vertical and horizontal) at different initial biomass concentrations for the TAG accumulation phase, during two distinct seasons (i.e. high and low light conditions).ResultsIncreasing IBS-light availability led to both a higher IBS-TAG production rate and TAG content at the end of the batch, whereas biomass yield on light decreased. As a result, an optimum IBS-light availability was determined for the TAG productivity obtained at the end of the batch and several guidelines could be established. The vertical reactor (VR) should be operated at an initial biomass concentration of 1.5 g L−1 to achieve high TAG productivities (1.9 and 3.2 g m−2 day−1 under low and high light, respectively). Instead, the horizontal reactor (HR) should be operated at 2.5 g L−1 under high light (2.6 g m−2 day−1), and at 1.5 g L−1 under low light (1.4 g m−2 day−1).ConclusionsFrom this study, the great importance of IBS-light availability on TAG production can be deduced. Although maintaining high light availabilities in the reactor is key to reach high TAG contents at the end of the batch, considerable losses in TAG productivity were observed for the two reactors regardless of light condition, when not operated at optimal initial biomass concentrations (15–40% for VR and 30–60% for HR).Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0283-2) contains supplementary material, which is available to authorized users.

Highlights

Microalgal triacylglycerides (TAGs) are a promising sustainable feedstock for the biofuel, chemical and food industry
The time-evolution of biomass concentration, TAG, intracellular nitrogen and carbohydrate contents, as well as the TAG productivity, are shown in Figure 1 for the run inoculated at 1.5 g L−1 in the vertical reactor under low light conditions
As a response to N-starvation, TAG content promptly increased (Figure 1b), while carbohydrate content decreased over time (Figure 1b), suggesting that TAGs represent the main storage compound for N-starved cells of Nannochloropsis sp

Summary

Introduction

Microalgal triacylglycerides (TAGs) are a promising sustainable feedstock for the biofuel, chemical and food industry. Industrial production of microalgal products for commodity markets is not yet economically viable, largely because of low microalgal productivity The latter is strictly dependent on initial-biomass-specific (IBS) light availability (i.e. ratio of light impinging on reactor ground area divided by initial biomass concentration per ground area). High value products from microalgae are already commercially available, industrial production of microalgal products for commodity markets is not yet economically viable, largely because of low microalgal productivity [1] In this respect, outdoor pilot-scale research, in addition to mechanistic studies under controlled laboratory. Outdoor pilot-scale research, in addition to mechanistic studies under controlled laboratory In both laboratory and outdoor studies, the important role of light availability (i.e. ratio of light impinging on the reactor surface divided by biomass concentration in the reactor) on lipid production has been highlighted [2, 3]. Higher lipid content was obtained by increasing light availability, whereas an opposite trend was observed for TAG productivity at the end of the batch cultivation.

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Discussion

Conclusion