Towards industrial production of microalgae without temperature control: The effect of diel temperature fluctuations on microalgal physiology

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 degrees 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 degrees C up to a maximum of 47.5 degrees C. The highest growth rate of 0.17 h-1 was obtained when applying a daytime peak temperature of 40 degrees C. Operating photobioreactors in tropical regions, with a maximal peak temperature of 40 degrees C, up from 30 degrees 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.

Automated summary

Regions with high levels of sunlight are ideal for microalgae production, but high temperatures can impact productivity and costs. Research shows that operating photobioreactors in tropical regions with reduced temperature control can decrease production costs and increase growth rates.