Elisa cararetoA large, clear glass tank called a photobioreactor, in which microalgae are grown in the open air, has been designed and developed by a multidisciplinary team of researchers from the Federal University of São Carlos (UFSCar) and the University of São Paulo (USP). Among its innovations is a porous membrane, used for filtering a culture medium containing sodium nitrate, phosphate, potassium, micronutrients, sulfate, and other inorganic elements, which is fed to cells of the microalga Chlorella vulgaris. Depending on the microalgae and nutritional compositions selected for use in the reactor, the membrane makes it possible to choose the type of biomass that will be obtained at the end of the process: proteins for animal feed, essential fatty acids like omega 3 to be used by the food and pharmaceutical industries, or carbohydrates used in the manufacture of plastics or fertilizers.
“Biochemical manipulation of microalgae enables us to produce the biomolecules that companies need for use as raw materials,” says Ana Teresa Lombardi, professor at the Center for Biological and Health Sciences at UFSCar and coordinator of the Research Partnership for Technological Innovation (PITE) project, which is part of a cooperation agreement between FAPESP and petrochemical company Braskem. “Among the many possible applications, one interesting and promising result we had was the pelletization [coating] of native Cerrado plant seeds with algal biomass. These seeds can be used in reforestation,” says Lombardi. The research was the topic of a master’s dissertation, already defended. “These seeds coated in algal biomass and mucilage are able to make better use of rainwater because of their stronger water retention, which can result in lower mortality of seeds planted in the field,” she emphasizes.
Lombardi explains that the algae cultivation process requires a continuous inflow of fresh nutrients. But the material occasionally overflows and the spent culture medium must be removed. “In a standard bioreactor, removing the spent medium also implies removal of cells. It’s as if we washed away the whole thing.” Given the membrane’s extremely fine pores, the nutrients used in the bioreactor will not be removed unless they are filtered out. This permits not only reusing the medium, but also choosing the density of cells that will remain in the tank and the culture medium that will be fed into the reactor by continuous flow. “The algae adapt quickly to nutritional changes because they undergo an intracellular transformation,” says Lombardi. In other words, they can change their biochemical composition according to their surroundings. “We have transformed this microbiological attribute of algae into a technological process,” says the researcher.
Algae like Chlorella provide a high yield of dry biomass that can be harvested several times a year. As photosynthesizing organisms, they transform luminous energy into chemical energy, which is stored in the chemical bonds that hold carbohydrate, fat, and protein molecules together. In addition to their high photosynthetic efficiency, algae also excel at fixing carbon dioxide (CO2. “The project’s main objective, carbon dioxide fixation, came as a consequence of biomass production using the photobioreactor,” says Lombardi. The way the equipment was built also permits a more efficient use of incoming solar energy, substantially increasing productivity. “In just 24 hours, we can get the algal population to replicate five times,” says the researcher.
The researchers initially planned to purchase a bioreactor in the Netherlands. While they waited for the vendor’s response, they started building a prototype with an initial capacity of 200 milliliters, in their own laboratory. Then, the group built a larger-scale, 200-liter model. “It was so promising that we changed our minds about importing [the equipment],” says Lombardi. The next step was to build a 1000-liter bioreactor with fully controllable variables. Achieving the ideal photobioreactor for the project took a lot of meetings among the four researchers, two of them from UFSCar (a biologist with a PhD in chemistry and a botanist specializing in zooplankton) and two from USP (a chemical engineer and two mechanical engineers). “We built a completely experimental 1000-liter photobioreactor in which all variables could be controlled,” Lombardi explains. To do this, all systems – agitation, sparging, filtering, and continuous flow – were assembled separately so they could function independently. “The independent continuous flow keeps the chemical environment relatively constant, which results in quality control over the final product.”
In its second year, the project gained reinforcements: a post-doctoral student with a degree in biology, PhD in mechanical engineering, and expertise in membrane filters. As a result, the reactor received commercially available submersible membranes that are “easy to operate and clean,” according to Lombardi. “It’s an important factor that distinguishes our reactor, as few others in the world offer this feature.” In December 2013, after three years and eight months, the project was concluded. But the group’s research on carbon fixation is ongoing. “We are now quantifying the maximum photosynthetic potential of the algae using a fluorescence-based method, which can also be applied to terrestrial plants.”
Photobioreactor grown microalgae as a tool for atmospheric CO2 mitigation (nº 2008/03487-0); Grant mechanism Research Partnership for Technological Innovation (PITE); Principal investigator Ana Teresa Lombardi (UFSCar); Investment R$320,670.46 (FAPESP) and R$312,314.00 (Braskem).
CHIA, M. A. et al. Lipid composition of Chlorella vulgaris (Trebouxiophyceae) as a function of different cadmium and phosphate concentrations. Aquatic Toxicology. v. 128-9, p. 171-82. 15 mar. 2013.