Using seaweed to reduce heavy metals in water

Heavy metals, like lead and cadmium, are naturally found at a low concentration level in aquatic environment, including oceans and rivers.  However, these heavy metals become a problem when humans dump these pollutants in large quantities without appropriate treatment.  Experts say that heavy metals are a key hazard on human health as well as the environment. 

A study published in Environmental Technology & Innovation last year identified “anthropogenic activities”, for example releasing wastewater and pesticides, as sources of heavy metals in aquatic environments.

Heavy metal poisoning is caused by the accumulation of toxic amounts of metals in the body due to exposure.  Heavy metals, including mercury, chromium and zinc, are fatal to humans even with exposure to just a small quantity, leading to serious illness such as cancer.

Heavy metals are also major environmental pollutants due to their toxicity, persistence and bio-accumulative nature.  Heavy metals can enter the food chain through marine life such as fish which in turn affect predators such as bigger fish, birds and mammals, including humans, which then migrate and transport the pollutant to different ecosystems.

Using kelp to mitigate the level of heavy metals

One solution to reduce the quantity of heavy metals in water is adsorption, the absorbing of contaminants on the water’s surface using adsorbents. Compared to other methods, adsorption does not release any secondary pollutants in the process.

To make this adsorption technique more “low-cost” and “environmentally friendly”, a group of Korean scientists recently suggested the use of a type of seaweed known as kelp, or kombu, as a substance that can effectively absorb contaminants in water.  Kelp, a type of large, brown seaweed, grows in shallow, nutrient-rich saltwater near coastal areas around the world.

In South Korea, there is an abundance of kelp as it is not considered a food source. Hence, a large amount of kelp found at seaweed farms is not being harvested but instead is discarded back into the ocean.

“A report says that almost 40 percent of algae produced by seaweed farms are not reused,” Jung Kyung-won and Choi Jae-woo, scientists at the Centre for Water Cycle Research, who led the study to use kelp as absorbents of heavy metals, told Maritime Fairtrade. 

“Also, they create a variety of environmental problems when they are washed up at beaches after natural disasters, such as typhoons.”

“Therefore, besides using kelp as an absorbent, by taking in the discarded kelp, we can also stop further environmental problems and reuse them in a useful and eco-friendly way,” the researchers said. “Our study showed that upcycled kelp can offer various benefits.”

In addition, the scientists explained that kelp, out of all seaweeds, can absorb double the amount of carbon dioxide that tropical rain forests can. Kelp also contains mineral substances, such as calcium and magnesium, which can eliminate contaminants more effectively than biomass from lands used in previous studies.

Ultimately, the scientists want to develop kelp-based biochar, a carbon-rich substance produced through the process of slow pyrolysis in which biomass is combusted under oxygen limitation, which is more efficient in water treatment and removal of pollutants. 

“Remediation techniques using biochar have been in the limelight recently, owing to its high pollutant reduction rate and low production cost (compared to other techniques),” Jung and Choi said.

The surface of most biochar is negatively charged, which means they will be less responsive to anionic pollutants, such as antimony, arsenic and chromium. Also, biochar consists of tiny particles, which complicates the process of recollecting pollutant-absorbed biochar particles. 

Throughout the study, the scientists tried to improve the biochar’s reactivity to anionic pollutants by coating it with micro-circular magnetic particles. They also used external magnetic force to facilitate the separation and recollection process of biochar particles.

The scientists tested their kelp-based biochar on tap water and river water and they could confirm almost 90 percent of antimony, one of the most representative heavy metal pollutants, was removed from the tested water.

The research team is positive of the commercial potential of the kelp-based biochar, which can eliminate different kinds of heavy metals and be used as a catalyst to remove other pollutants.

“South Korean seaweed farms discard a large amount of kelp every year,” Jung and Choi said. “Therefore, making biochar with discarded kelp is an environmentally friendly endeavor and can also contribute to carbon neutrality and the security of our water resources.” 

Sunny Um

Sunny Um

Sunny, our South Korea correspondent working out of Seoul, is a journalist with a passion for community journalism and an interest in economics and politics.

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