Nanomodified sugarcane bagasse can ‘clean up’ water contaminated by copper or chromium

Hybrid material made from magnetite nanoparticles sticks to contaminants and can be removed from water by a magnet. The technique can be adapted for use in removing synthetic dyes, drugs, hormones and pesticides.

By Luciana Constantino  |  Agência FAPESP – Sugarcane bagasse, one of the main residues of Brazilian agroindustry, has proved promising for use in decontaminating water with high levels of potentially toxic metallic ions. A composite (a hybrid material with different characteristics from its precursors) produced from bagasse and magnetic nanoparticles removed copper and chromium from water in a study conducted by Brazilian researchers. Results of the study yielded the publication of two articles in Environmental Science and Pollution Research.

Copper is malleable and a good conductor of electricity – hence its widespread use in industry, construction and agriculture. It is also used to control the proliferation of cyanobacteria (blue-green algae) in reservoirs storing water for human consumption. Small amounts of copper are essential to living organisms, but large amounts in water can cause vomiting and diarrhea.

Most emissions of chromium (Cr) into the environment originate in human activity, such as tanning and dyeing, among other industrial processes. Its toxicity depends on the degree of oxidation: Cr(VI) is the most toxic form and considered a carcinogen, while Cr(III) is an essential micronutrient for the maintenance of the human metabolism. Owing to its adverse effects and the large amount of industrial waste containing Cr(VI), novel techniques using biosorbents have been proposed for its removal from water and effluent.

The researchers developed a composite of bagasse (biomass waste from the processing of sugarcane by ethanol and sugar plants) and synthetic magnetite nanoparticles. The composite has adsorbent and magnetic properties, and efficiently removes different chemical contaminants from water.

After removing the contaminants by adsorption (adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface), the material was withdrawn from the water by a magnet, leaving the water clean. “Its hybrid nature combining the properties of the biological matrix [sugarcane bagasse] and the physicochemical properties of magnetite makes it highly versatile and selective regarding the chemical species of interest. In other words, there is space for studying the application of this material to species such as organic molecules [synthetic dyes, drugs, hormones and pesticides], reinforcing its potential as a bionanocomposite for treating water and effluent,” according to the articles “Nanomodified sugarcane bagasse biosorbent: synthesis, characterization, and application for Cu(II) removal from aqueous medium” and “Hexavalent chromium removal from water: adsorption properties of in natura and magnetic nanomodified sugarcane bagasse”.

The first authors of the articles are students Juliana Tosta Theodoro Carvalho (former) and Thais Eduarda Abílio (latter), supervised by Elma Carrilho, a researcher at the Polymeric and Biosorbent Materials Laboratory (Lab-MPB) of the Federal University of São Carlos (UFSCar) in Araras (São Paulo state, Brazil). Carrilho is the last author, and the penultimate author is Geórgia Labuto, a researcher at the Laboratory of Integrated Sciences (LabInSciences) of the Federal University of São Paulo (UNIFESP) in Diadema. The research line is funded by FAPESP and the National Council for Scientific and Technological Development (CNPq).

According to Carrilho, the study was part of a series being conducted by the group at UFSCar’s Lab-MPB using biomass as a biosorbent, which proved to be a viable and efficient alternative for decontamination of aquatic environments. For example, one of the projects, supported by FAPESP, involved the development of an adsorbent material made from yeast biomass (also a byproduct of the sugar and ethanol industry).

“The proposal for these materials is to create fixed-bed adsorption columns containing the adsorbent composites produced from biomass residues normally disposed of as waste, to act as biosorbent filters,” Carrilho said. “We hope scientific production based on the use of this kind of technology continues to grow in Brazil and to drive the nation’s bioeconomy.”

Carrilho noted the considerable increase in the number of studies involving biosorption produced by Brazilian scientists in recent years. The biosorbents most researched in the period are derived from plants, followed by algae and microorganisms. This information is in the chapter by Carrilho and Labuto of the book Bioremediation and Bioeconomy, published in 2016.

Potential

Interest in research on biomaterials and processes capable of removing contaminants such as hormones, metals and pesticides from an aqueous medium has grown in recent years, especially in response to the prospect of future water shortages, Carrilho stressed.

The amount of available freshwater per person in the world has fallen more than 20% in the last two decades, according to The State of Food and Agriculture 2020, issued by the UN Food and Agriculture Organization (FAO) in November. “Improved water management, supported by effective governance and strong institutions – including secure water tenure and rights, underpinned by sound water accounting and auditing – will be essential to ensure global food security and nutrition,” it says.

About 2.2 billion people do not have access to safe drinking water, and 4.2 billion lack proper sanitation. Owing to the impact of climate change, by 2050 between 3.5 billion and 4 billion people will have limited access to water, 1 billion of them in cities.

Only about 3% of the world’s water is fresh, and only half of that is readily available; the rest is locked up in glaciers, inaccessible aquifers and so on. Brazil has 12% of the world’s freshwater. Because the amount of water that circulates continuously throughout the planet remains constant, treatment is increasingly important, but 80% of wastewater is untreated before being discharged into the environment.

Other applications

The magnetic nanocomposites studied by the group, Carrilho explained, also have the potential to help remove crude oil and similar fluids from water surfaces in the event of a spill.

Laboratory tests performed by the scientists have shown that other composites made from waste biomass and magnetite can be used to clean up oil spills with 80% efficacy. This project was also supported by FAPESP (more at: agencia.fapesp.br/32264/). 

The article “Nanomodified sugarcane bagasse biosorbent: synthesis, characterization, and application for Cu(II) removal from aqueous medium” is at: link.springer.com/article/10.1007/s11356-020-11345-3 and the article “Hexavalent chromium removal from water: adsorption properties of in natura and magnetic nanomodified sugarcane bagasse” is at: link.springer.com/article/10.1007/s11356-020-11726-8.