(229a) A Novel Multiscale Model Approach to Describe Products Formation during the Cultivation of Haematococcus Pluvialis Under Different Environmental Conditions

Authors: 
Usai, A., University of Manchester
Theodoropoulos, C., The University of Manchester
Pittman, J., The University of Manchester
Bioprocess development represents an onward challenge for world sustainability, and economy. Microalgae as bio-factories of the future are currently facing an increasing interest” as they possess a range of interesting properties. The photoautotrophic growth of microalgae is based on the absorption of carbon dioxide as main carbon source, making them a promising tool for dissipating the continuously increasing CO2 in the atmosphere (Singh & Ahluwalia, 2013). The cultivation of microalgae could be inserted in a wider context of bio-refinery exploitation due to their capability to produce high-value molecules, biofuels, fertilizers, antioxidants, anti-inflammatory, and antimicrobials making them potentially exploitable in a refinery context (Chew et al., 2017). Furthermore, these properties are key aspects to be improved when the bio-refinery concept have to be developed (García Prieto, Ramos, Estrada, Villar, & Diaz, 2017).

Haematococcus pluvialis is able to produce significant amounts of compounds belonging to lipids and starch classes, and various specific pigments such as astaxanthin, and lutein (Shah, Liang, Cheng, & Daroch, 2016). Their production could vary depending on the environmental stress conditions such as light intensity and nutrients concentration (D’Alessandro & Antoniosi Filho, 2016). However, stress conditions lead to undesired phenomena such as cell lysis (Hata, Ogbonna, Hasegawa, Taroda, & Tanaka, 2001), which is likely to be related with products release in the external cell environment and eventually with their loss. Photoautotrophic processes are usually characterised by long term cultivations, which make their exploitation even more difficult when compared with other kind of cultivations such as mixotrophic or heterotrophic. Nevertheless, photoautotrophic growth has been indicated such a convenient option to produce specific compounds as lutein, due probably to the low complexity and economy of the cultivation system (Lin, Lee, & Chang, 2015).

This work aims to develop a novel multiscale model of the photoautotrophic growth to optimise the production of lipids and pigments. H.pluvialis undergoes a transition from a vegetative (green) to a cyst (red) stage during the nutrient depletion. Cells in the vegetative stage are dimensionally smaller than cells in the cyst stage, and their membranes are thinner. Hence, cells are susceptible in different ways to cell rupture during nutrient depletion, which leads to cell number loss. Cell growth, product formation, the cell lysis, are described through the development of a segregated model based on Population Balance Equations (PBEs), making possible the description of the relationship between cell dimension/transition, cell loss, and products availability. Cell volume is a key state of the population balance model, and its link with the intrinsic concentrations of nutrients and products are presented. Model parameters are fitted against experimental data, and their predictive capabilities are tested. The subsequent expansion of the model to heterotrophic cultivations is also exploited.

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