Activated carbon tends to stand out as a favorite tool in the arsenals of water treatment plant operators who battle the negative effects of harmful algal blooms.
The black, crumbly substance that’s derived from specially prepared organic materials facilitates a chemical process known as adsorption, in which cyanotoxins that find their way into the raw water supply adhere to its surfaces. Adsorption tends to be the most convenient and effective among a handful of techniques to remove toxins.
Dr. Dragan Isailovic, professor in the Department of Chemistry and Biochemistry, holds a corncob sample in his lab. He and his collaborators evaluated carbonized corncobs for the removal of cyanotoxins from water in research published in the journal Separations.
But there are environmental and economical drawbacks to commercial activated carbon, which often is derived from coal and not reasonably regenerated after a single use.
At The University of Toledo, chemists are exploring an alternative to commercial activated carbon that uses a common agricultural byproduct. Their most recent research, published in the peer-reviewed journal Separations, indicates that carbonized corncobs are as effective at removing several targeted cyanotoxins in laboratory experiments as the commercial version used at the water treatment plant in Toledo.
“Our corncob-based biochar and activated carbon were almost 100% effective at removing microcystin in preliminary experiments,” said Dr. Dragan Isailovic, lead author and a professor in the UToledo Department of Chemistry and Biochemistry. “The research is very promising but more experiments are needed before we can say whether they will be as effective as commercial activated carbon at the scale required by a water treatment plant.”
Treatment plant operators turn to activated carbon in cases where cyanobacteria cells break down and release cyanotoxins into the raw water supply, as occurred in western Lake Erie during the water crisis that left half a million residents without safe tap water for three days in 2014. Toxins, such as microcystins, are more complicated to remove than intact cyanobacteria.
Activated carbon is not exclusively derived from coal. Versions derived from wood, peat and coconut are commercially available, and researchers are experimenting with agricultural waste products including peanut hulls, almond shells and grasses.
Dr. Michal Marszewski, Manjula Kandage, Hasaruwani Kiridena, Yohan Sudusingha, Dr. Sharmila Thenuwara and Dr. Dragan Isailovic evaluated carbonized corncobs for the removal of cyanotoxins from water in research published in Separations.
Isailovic and his collaborators joined the latter in publishing research on rice husks in the peer-reviewed journal Science of the Total Environment in 2019. The UToledo team is building on what they learned with rice husks in their current research, while shifting their focus to an agricultural waste product that’s demonstrating even more potential.
“There are many cornfields in northwest Ohio and across the United States, where the corncobs are often discarded or burnt,” Isailovic said. “So it makes sense to look to corncobs rather than coal, wood, peat or coconut when we’re producing activated carbon. We’re excited about their potential as an economical and environmental alternative.”
The corncobs used in the experiments were donated by The Andersons in Maumee, where product manager Norman Peiffer selected appropriate products for the study, assisted by Dr. Michal Marszewski, assistant professor in the UToledo Department of Chemistry and Biochemistry, and other co-authors on the Separations article: Hasaruwani Kiridena and Manjula Kandage, both doctoral candidates in the department, and Dr. Sharmila Thenuwara, a postdoctoral researcher in the department.
Then team chemically treated and then heated the corncobs, in processes intended to increase surface area and porosity — factors that are key to the adsorption process. They created biochar by refluxing the corncobs with hydrochloric acid and heating them to 250, 300 or 350°C and created activated carbon by chemically activating the corncobs with phosphoric acid and heating them in a nitrogen atmosphere at 500°C.
Then the team conducted a series of experiments with samples of water taken from western Lake Erie during harmful algal blooms from 2020 to 2022. They found that both biochar and activated carbon eliminated a significant amount of the targeted forms of cyanotoxin under various conditions, with the activated carbon working more effectively than the biochar. Each gram of activated carbon was able to adsorb approximately 20 milligrams of toxins, including several microcystin congeners and nodularin-R.
A sample of corncobs, left, and activated charcoal.
The research is funded under the fifth round of the Ohio Department of Education’s Harmful Algal Bloom Research Initiative, which supports applied research at state universities aimed at solving the harmful algal bloom problem in Lake Erie. The initiative, which is led by representatives from UToledo and Ohio State University and managed by Ohio Sea Grant, arose out of the water crisis in 2014.
Isailovic, a member of the water task force that brought together faculty scientists, engineers, lawyers, medical doctors and public health experts at UToledo in the immediate wake of the “do not drink” warning in 2014, has so far led four projects under the Harmful Algal Bloom Research Initiative, including another fifth-round project aimed at identifying novel cyanotoxin congeners in western Lake Erie and inland lakes in Ohio.
Isailovic said the team’s research into carbonized corncobs for the removal of toxins will continue, with researchers already excited about a new way to produce the activated carbon from raw corncobs that they’re exploring in the laboratory.
