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11 January 2023

Protecting soil and water from contamination through biochar

TWAS awardee Anushka Rajapaksha uses materials to protect natural resources in Sri Lanka from contamination by pharmaceuticals and heavy metals

Sri Lanka has some difficult environmental problems that are common throughout the world, including wide-spread dumping sites, and pollution that contaminates agricultural soil and well water. But Anushka Rajapaksha, winner of the 2022 TWAS-Atta-ur-Rahman Award in Chemistry, is employing and improving upon one possible solution: a chemical-capturing substance called biochar.

The annual award is sponsored by Pakistani TWAS Fellow Atta-ur-Rahman, a leading scholar in the field of organic chemistry and a globally influential advocate of science education. The award, which includes a US$5,000 prize, is given to a young chemist in a scientifically lagging country and aims to inspire young researchers in these nations to pursue chemistry careers.

 “Winning this award is really an encouragement as an early-career researcher, and it provides international recognition for my contribution in the field of chemistry,” Rajapaksha said. “Hardships offer unexpected gifts if you believe in yourself to embrace the silver linings. I’m really happy and it’s a great honor.”

Real-life applications

Biochar is a carbon-based, charcoal-like substance produced by carefully burning plant matter through a controlled thermo-chemical process. It is increasingly popular as a means to capture carbon as well as improve soil quality, Rajapaksha said, and it can be applied to soil to snare leaching contaminants like heavy metals and pharmaceuticals out of the environment before it renders soil and water reservoirs too toxic for human use.

“It’s fairly common for local people to use charcoal instead,” she noted, “but engineered biochar can prove superior for this particular job.”

In Sri Lanka, local populations often depend heavily on groundwater from wells that are in danger of being contaminated by chemicals in the soil. Sometimes the contamination even comes from natural sources, such as chromium, nickel, cobolt and manganese found in red-soil areas where vegetation is naturally scarce. But local people, all the same, need to consume water from dug wells, even if they don’t have facilities for cleaning a large amount of water after-the-fact.

Rajapaksha and her team collected field data on groundwater contamination in several such locations and collected groundwater where Sri Lankan wells were contaminated with heavy metals. They then conducted lab experiments, placing biochar directly into the contaminated water to observe the results. In one study they found that, in the lab, the biochar removed up to 76% of chromium from the water, and published their results in the journal Environmental Research. They also successfully produced findings supporting the idea that clay materials could help remove nickel from the water, according to a study published in Colloids and Surfaces A: Physicochemical and Engineering Aspects.

Rajapaksha and her colleagues plan to make water filters out of this biochar that rural people can use to filter their local groundwater specially where fluoride has been a burden. In time, they will return to these locations to introduce biochar, which can be mixed directly with the soil to function as a filter and capture toxic heavy metals before they seep into the groundwater.

Engineering biochar

Rajapakshas’ work has mainly focused on modeling the specifications of biochar—its exact chemical and physical make-up—in order to better-suit varied situations in the environment. For example, she recalled, sometimes Rajapaksha’s team increased the size of pores in the biochar material by varying the materials and methods used to create it, thus increasing its surface area, making it able to absorb and hold more contaminants that would otherwise poison water and soil.

They also conduct experiments using large cylinders, or “columns” of biochar, to see the effect the substance has on the chemical condition of the soil around it over time.

Biochar is also a special tool in that it both protects the environment, and serves as a way to reuse waste on a large scale. Rajapaksha and her team normally just make garbage into biochar, especially because Sri Lanka has problems with waste management and a prevalence of dumping sites. So biochar can be a productive way to both dispose of trash and keep water clean. But there are other options as well, which can help preserve the environment from a completely different angle: removing invasive species.

“To prepare this biochar, we use different materials,” she said. “For a few studies, we used invasive plant materials—we remove them from the environment because they are troublesome, then convert them into biochar.”

Sean Treacy

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