Funded by Shell Brazil, the project involves several Brazilian research institutions and promises to be a way to mitigate the damaging effects of greenhouse gas emissions.

The sequestration of carbon dioxide (CO2) via nature-based solutions is one of the most exciting efforts to lessen the effects of greenhouse gases released into the atmosphere. Generally speaking, these technologies present great disruptive potential that start a new value chain in the capture, use, and storage of carbon. This is the case of a hydrogel, which is being developed under the Hydrogel Program, funded by Shell Brazil, with resources from the R&D Investment Clause of the Brazilian National Petroleum, Natural Gas and Biofuels Agency (ANP) Concession Contracts, and which involves several institutions from the University of São Paulo (USP) under the leadership of the FAPESP Shell Research Center for Gas Innovation (RCGI), as well as the Federal University of Rio Grande do Sul (UFRGS).

Hydrogel, consisting of organic material, will be produced with molecules synthesized from CO2. After being applied during the planting process, the product’s granules will degrade and free the carbon to be stored in the soil. According to Shell executive and Deputy Director of the RCGI Alexandre Breda, the product will be developed by the Federal University of Rio Grande do Sul (UFRGS) from oxalic acid and a bio-monomer. The oxalic acid will be produced from CO2 by the Polytechnic School of USP (Poli-USP), in collaboration with the Institute for Energy and Nuclear Research (IPEN) and the Brazilian Agricultural Research Corporation (EMBRAPA).

Once it is ready, hydrogel will be tested by USP’s Luiz de Queiroz College of Agriculture (ESALQ/USP). At the same time, USP’s Institute of Energy and Environment (IEE/USP) will propose the necessary normative standards for the product to go on the market. The IEE already focuses on producing normative documents for the global application of this type of technology, in accordance with international standards. The work covers both nature-based solutions and those that make it possible to transform CO2 into high added-value chemical products.

CO2 sinkhole – Indicated as being one of the main gases causing the greenhouse effect and climate change, the amount of CO2 in the atmosphere has been growing due, mainly, to the burning of fossil fuels. The storage of excess carbon is an urgently recommended action to help mitigate the greenhouse effect. And the soil, which naturally performs this storage process, has the potential to be a great CO2 sink. This is where ESALQ’s role in hydrogel testing comes in.

“In addition to quantifying CO2 storage, we want to know what are the possible benefits of hydrogel for soil and plants under tropical climate conditions,” says research coordinator Carlos Eduardo Pellegrino Cerri, Professor in ESALQ’s Soil Science Department. He states that when an organic material decomposes in the soil, part of the carbon dioxide generated is retained in the earth and the rest returns to the atmosphere in the form of gas: “Under natural conditions, approximately 1/3 of the carbon is retained in the soil. What we are looking for is how much of the carbon in the hydrogel will be stabilized in the soil under tropical conditions.”

When added to CO2 storage in the soil, the oxalic acid produced by Poli will have a negative carbon footprint during the capture process. According to Thiago Lopes, who responsible for this part of the research, the CO2 will be transformed into oxalic acid via the electrochemical and/or photo-electrochemical path. “On this path, the carbon footprint of oxalic acid would be negative. In other words, by using electricity (or photons) from renewable sources, we could capture nearly two CO2 molecules to produce oxalic acid.”

Soil-Plant relationship – Another challenge for the study is to evaluate the performance of hydrogel in the soil-plant relationship. The expectation is that the product’s granules, once dampened, will retain water and gradually release it to the plant, which would reduce the need for irrigation, increase the absorption of macro and micronutrients by the plant, and confer benefits to the properties of the soil.

“The fact that hydrogel is biodegradable offers advantages that go beyond the environmental issue. One of them is to increase the rate of absorption of micronutrients, something that only occurs in the soil solution. Another is to provide favorable conditions for the proliferation of beneficial microorganisms in the soil, which would potentially increase competition with disease-causing pathogens,” Cerri states.

One of the most interesting aspects of this study has to do with the exchange of cations in the soil. According to Cerri, a good share of the elements that a plant absorbs have a positive charge, that is, they are cations. Nevertheless, Brazilian soil has little negative charge, which means that many of the nutrients with a positive charge end up not fixed in the soil and are lost by leaching. “The proposal is to use hydrogel with clay to increase the negative charge in the soil and, thus, maximize the exchange capacity of cations,” he says.

It will be the responsibility of the Chemical Institute of the Federal University of Rio Grande do Sul (UFRGS) to produce a hydrogel that has this capability.  The work is being led by Professor Douglas Gamba, from the Department of Organic Chemistry, and foresees the use of oxalic acid produced by IPEN, with its ethyl ester derivatives, in addition to products from renewable sources, such as glycerol and/or polyglycerol and different natural hydroxy carboxylic acids. This composition will result in a hydrogel having high absorption and retention capacity for cations in the soil.

The initial testing at ESALQ will be done within closed systems that provide better control of the experiments. Field evaluations will come later. Tests are planned with five cultures of varying cycles: grasses, soybeans, corn, eucalyptus, and sugar cane, for example. The first results should come out in less than two years. “After four years, we expect to have enough robust data to support decision making regarding the potential use of this hydrogel in Brazilian agrosystems.”