Project studies how to transform CO2 into bioethanol and green plastic

An initiative by USP and UNIFESP researchers is confident in a natural process, without chemical additives, through microalgae found in mangroves and cyanobacteria


Capture carbon dioxide (CO2) via algae and cyanobacteria and generate high aggregate value products, like biofuels and green plastic, in a natural and sustainable manner.

The investigation of these possibilities is the objective of Bioassisted CO2 capture and conversion into bioproducts performed within the scope of the Research Centre for Greenhouse Gas Innovation (RCGI), funded by Shell of Brazil and by the São Paulo Research Foundation (FAPESP).

“The term ‘bio-assisted CO2 capture’ means that the process is carried out naturally and biologically, that is, without chemical additives. In our case, we use two microorganisms – microalgae and cyanobacteria – that perform photosynthesis,” explains the project’s lead coordinator, biologist Elen Aquino Perpetuo, Professor in the Instituto do Mar at the Baixada Santista campus of the Federal University of São Paulo (UNIFESP) and collaborating researcher at CEPEMA-POLI-USP.

Regarding microalgae, the concept is that in addition to the capture and fixation of CO2, their biomass can be fermented in reactors for the production of bioethanol, also known as third-generation ethanol. “Biofuels from these biomasses have attracted extensive attention, since algae can be cultivated with CO2 and sunlight, using salt or brackish water on uncultivable land, in addition to not having lignin in their composition. For the production of third-generation ethanol, it is crucial to expose the intracellular components of algae, and hydrolysis is the process used for this purpose. The cell wall of algae is the main structure that must be depolymerized to extract polysaccharides. During the conversion process, the polysaccharides will be broken down into monomers which, in turn, will be fermented and converted into ethanol.”

The microalgae that will be used in the experiment, such as Parachlorella kessleri, were collected in mangrove areas. “The mangrove is an environment with a high level of organic matter, along with anthropogenic pollution. Therefore, these microalgae are extremely resistant and adapt well to any situation, thus favoring our research,” notes Ms. Perpetuo. According to her, in addition to mangroves, microalgae can be found in oceans and rivers, and can be cultivated in artificial breeding sites. “The states of Rio Grande do Norte and Paraíba already have microalgae farms.”

One of the project’s challenges is how to produce large volumes of bioethanol with microalgae. “We know that the biotechnological process works very well on a reduced pilot scale of 100 liters, for example, but when it comes to the production of thousands of cubic meters, we still don’t know what the result will be,” says Elen.

The project team investigates which species of microalgae are capable of accumulating a higher carbohydrate concentration. “This carbohydrate will be hydrolyzed and processed in a large reactor. We want to find out if this will make it possible to produce quality biofuel on an industrial scale,” she explains.

The researchers are also studying the possibility of using bagasse (a polluting waste generated during the production of sugarcane ethanol) as a medium for cultivating microalgae. “The disposal of bagasse is a headache for the sugar and alcohol industry due to its high cost. Not to mention that the residue is commonly used as a fertilizer in the fertigation of crops, with the risk of leaking into the water table and causing environmental damage. The objective is to achieve aggregate value for the bagasse through microalgae, which would be positive for the plants and for the environment,” Elen points out.

The researcher does not hide her enthusiasm for the results that could be gained from the experiments with microalgae. “It is a cheap technique that can produce a green fuel, which is not derived from petroleum and, therefore, less polluting and with no dependence on fossil reserves. But that’s not all: we are also talking about a Brazilian product, free from the fluctuations of the international market that impact the final consumer’s pocket.”

Another focus of the project, led by professors Renato Sanches Freire and Cassius Vinicius Stevani, both from USP’s Chemistry Institute (IQ), seeks to enhance the production of biopolymers through cyanobacteria, which are photosynthetic organisms that have characteristics of both algae and bacteria. When subjected to stress conditions in a culture medium with excessive light, cyanobacteria capture CO2, producing a type of bioplastic inside it with granules of polyhydroxybutyrate (PHB), as demonstrated in previous research.

“Nature is amazingly wise. Under extreme conditions, such as limited nutrients, especially nitrogen, and excessive carbon, cyanobacteria create a ‘fat’ reserve to ensure their survival, just like bears do during hibernation. This cyanobacterial reserve granule has the same characteristics as a polymer and, when extracted, resembles a plastic-film,” reports Ms. Perpetuo. “The goal of the project is to genetically modify cyanobacteria of the genus Synechocystis sp., so that it can accumulate even more of these biopolymers,” she explains.

The production of PHB is still in its infancy in Brazil and only takes place in a factory in the interior of São Paulo, where it is made from sugarcane and not from captured CO2. “The entire production is exported to Europe, where the plastic is mostly used in orthopedic prostheses. Since this plastic is biodegradable, the prostheses experience a low rate of rejection by the body,” explains Elen.

One of the challenges for expanding the use of PHB is its high cost. “It is considered to be one of today’s prime plastics, which is worth five times more than plastics of fossil origin, such as PET bottles. For the domestic market, this is an extremely high value. However, in my view, the environmental benefits outweigh the other costs involved. PHB is a biodegradable plastic, which will not remain in nature for a long time, unlike plastics of fossil origin. We need public policies that encourage research and innovation, as well as those that offer tax incentives for green companies,” Elen concludes.

Light excess stimulates Poly-beta-hydroxybutyrate yield in a mangrove-isolated strain of Synechocystis sp. (2021) GRACIOSO, BELLANA, A, KAROLSKI, B, CARDOSO, LOB, PERPETUO, EA, NASCIMENTO, CAO, GIUDICI, R, MOROSINOTTO, T. Bioresource Technology, 320 (B), 124379.

Extracellular carotenoid production and fatty acids profile of Parachlorella kessleri under increased CO2 concentrations (2021). JESUS, PCC, MENDES MA, PERPETUO, EA, BASSO, TO, NASCIMENTO, CAO.  Journal of Biotechnology, 329, 2021, Pages 151-159.