Abstract
Regions that offer high levels of sunlight are ideal to produce microalgae. However, as a result of high light intensities, the temperature in photobioreactors can reach temperatures up to 50 °C. Control of temperature is essential to avoid losses on biomass productivity but should be limited to a minimum to avoid high energy requirements for cooling. Our objective is to develop a production process in which cooling is not required. We studied the behaviour of thermotolerant microalgae Picochlorum sp. (BPE23) under four diel temperature regimes, with peak temperatures from 30 °C up to a maximum of 47.5 °C. The highest growth rate of 0.17 h−1 was obtained when applying a daytime peak temperature of 40 °C. Operating photobioreactors in tropical regions, with a maximal peak temperature of 40 °C, up from 30 °C, reduces microalgae production costs by 26.2 %, based on simulations with a pre-existing techno-economic model. Cell pigmentation was downregulated under increasingly stressful temperatures. The fatty acid composition of cell membranes was altered under increasing temperatures to contain shorter fatty acids with a higher level of saturation. Our findings show that the level of temperature control impacts the biomass yield and composition of the microalgae.
Highlights
Microalgae are photosynthetic microorganisms that can be grown using sunlight as an energy source
We study the response of the green temperature-tolerant microalgae strain Picochlorum sp. (BPE23) to diel fluctuating temperatures (Henley et al, 2004)
These tempera ture profiles were selected to mimic temperature conditions as found in outdoor photobioreactors placed under Caribbean climatological con ditions
Summary
Microalgae are photosynthetic microorganisms that can be grown using sunlight as an energy source. As a result of exposure to high light in tensities, the culture temperature in a photobioreactor can increase up to 50 ◦C (Bechet et al, 2010; Bleeke et al, 2014) This exceeds the opti mum temperature of most industrial microalgae, which is between 20 ◦C and 30 ◦C (Mata et al, 2010; Ras et al, 2013). While me chanical cooling, shading or spraying of water can offer a solution, applying these cooling methods should be avoided as much as possible due to their negative economic and environmental impact (Ruiz et al, 2016) These high temperatures only occur for a few hours each day, at midday. If species are able to grow optimally at a diel peak temperature of 40 ◦C instead of 30 ◦C production costs decrease by 26.2 %, while a peak temperature of 45 ◦C would reduce production costs by 28.4 %, as calculated by the techno-economic model of Ruiz et al, using climatological conditions as found in Curacao (Ruiz et al, 2016)
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