Researchers cultivate microalgae for biofuel production

A group of scientists at the State University of Campinas (UNICAMP) in Brazil have cultivated microalgae in a laboratory in order to use their metabolites, particularly lipids, for the production of biodiesel. An article in the journal Biomass Conversion and Biorefinery describes the research.

“It’s also possible to extract protein and carbohydrates and use them as food, in addition to obtaining products that can be used in cosmetics, such as beta-carotene and other valuable compounds, including phycocyanin, a natural blue pigment,” said Luisa Fernanda Ros, the article’s second author. She added that microalgae, which can be blue, green, or brown, are frequently responsible for the color of the sea and rivers.

Ros and her co-authors are all affiliated with the Laboratory for Optimization, Design, and Advanced Control (LOPCA) at the School of Chemical Engineering (FEQ) of Universidad Nacional Autónoma de Campinas (UNICAMP). Leonardo Vasconcelos Fregolente is the final author of the work. The initial individual is Bianca Ramos Estevam. Rubens Maciel Filho is the other contributor.

The study compared the behavior of the microalga Botryococcus terribilis in closed and open systems in terms of its development and productivity. Photobioreactors are closed systems in which there is no exchange of air with the environment and the conditions can be strictly controlled. Raceways are shallow artificial ponds or channels in which microalgae, water, and nutrients circulate and oxygen is exchanged with the surrounding environment.

Proteins, carbohydrates, lipids, pigments, and hydrocarbons were extracted and measured, according to the article. Hydrocarbons extracted from B. terribilis were characterized for the first time. The authors state, “Studies on B. terribilis cultivation have great economic and environmental significance but are rarely discussed in the literature.”

Ros stated, “Microalgae are the most ancient microorganisms and produce up to 50 percent of the oxygen we breathe.” Together, microalgae and fungi created the organic matter known as plants today.

Microalgae, like plants, develop via photosynthesis, converting carbon dioxide, water, and sunlight into energy while producing oxygen as a byproduct. The resulting metabolites include proteins, carbohydrates, and lipids, as well as lesser amounts of carotenoids, chlorophyll, and vitamins.

Microalgae deposited on the seafloor and deep underground are also a component of petroleum. Ros, who holds a Ph.D. in chemical engineering from UNICAMP, stated, “Imagine how many important things are contained within these cells.”

Strategy based on stress

Each microalgal cell divides into two identical progeny cells, resulting in exponential multiplication. “We cultivate microalgae in the laboratory to extract these biocompounds from their cells. Ros stated, “In order to do so, we must kill them, but this is not a problem as they reproduce rapidly and are always abundant.”

B. terribilis oils are appropriate for biofuel synthesis due to their high concentrations of saturated and monounsaturated fatty acids and long-chain hydrocarbons. The research serves to close the knowledge gap regarding the cultivation, stress, and chemical composition of these microalgae, thereby facilitating decisions regarding cultivation parameters and biorefinery applications.

In this instance, stress refers to a dearth of essential growth nutrients such as phosphorus or nitrogen. “When an organism detects a dearth of these nutrients, it begins to store lipids for survival. We utilized this capacity as a strategy for accumulating the metabolite of interest. In other terms, we subjected the organism to stress by removing growth-promoting nutrients. In addition, the proportion of other metabolites, such as proteins and carbohydrates, decreased as the organism grew more slowly. “It is essential to identify the compound of interest and achieve the proper equilibrium for the study,” Ros said.

The production of lipids and hydrocarbons increased by 49% and 29%, respectively, while the proportion of proteins decreased from 32% to 26%. Similar proportions of carbohydrates (15 percent of total) and carotenoids (0.41 percent to 0.86 percent) were found in stressed and unstressed growth.