Combining phytoremediation potential of Lemna gibba with biochar adsorption technology for cadmium, nickel and lead removal from wastewater

Water is the lifeblood of our planet, but it is increasingly burdened by invisible toxins. Among the most dangerous of these are heavy metals like cadmium, nickel, and lead. These elements do not break down or disappear; instead, they persist in the environment, accumulating in soil and water until they reach levels that harm ecosystems and human health. They enter our rivers and wetlands through industrial waste, mining, and agricultural runoff, posing serious risks such as kidney disease and neurological disorders. Because these metals are so stubborn, cleaning them up is difficult. Traditional methods often rely on expensive chemicals or energy-intensive machinery that many developing regions cannot afford. This has led scientists to look toward nature for answers, specifically at the ability of living plants to drink up pollutants and the potential of turning those plants into materials that can trap toxins.

In a recent study, researchers in Malaysia and Iraq explored a two-part strategy to tackle this problem using a small, floating aquatic plant known as duckweed, specifically the species Lemna gibba. This plant is common in local waterways and grows quickly, making it a promising candidate for cleaning water. The team investigated a dual approach: first, they tested how well the living plant could remove cadmium, nickel, and lead from contaminated water. Second, they took the same plant after it had done its work, dried it, and heated it in a controlled environment without oxygen to create a charcoal-like substance called biochar. They then tested this biochar to see if it could act as a powerful sponge to absorb the metals. The goal was to see if using the plant twice—once alive and once as a processed material—could offer a low-cost, sustainable way to purify wastewater.

The researchers began by creating artificial wastewater in the lab, mixing water with precise amounts of cadmium, nickel, and lead at concentrations ranging from 0.5 to 5.0 milligrams per liter. They placed 30 grams of the living duckweed into containers holding three liters of this polluted water and watched what happened over fifteen days. They measured the metal levels daily to track how much the plant absorbed. The results were striking. The living duckweed proved highly effective, removing nearly all of the lead and cadmium from the water, even at higher concentrations. Nickel was also removed efficiently, though slightly less so than the other two metals. The process was rapid at first, with the plant soaking up the majority of the toxins within the first ten days, before slowing down as it reached its limit. However, the study noted that the heavy metals did take a toll on the plant; by the end of the experiment, the leaves had turned yellow, a sign of stress caused by the toxic environment.

While the living plant worked well, the researchers wanted to know if the plant could do even more after its life cycle ended. They took the duckweed, dried it, and heated it to create biochar, a process that yielded about 44.5 percent charcoal from the original plant material. When they examined this new material under a microscope, they saw that it had become highly porous, filled with tiny holes and channels that provided a vast surface area for trapping metals. They then placed this biochar into fresh batches of contaminated water to see how well it adsorbed the toxins. The biochar performed exceptionally well, often clearing the water of metals more efficiently than the living plant, though the speed varied by metal and concentration. While the living plant required up to 15 days to reach maximum removal, the biochar achieved equilibrium within 12 to 48 hours, with some concentrations reaching full removal in just one day. The biochar showed a particular strength in grabbing lead, followed by cadmium and then nickel, likely due to the specific chemical properties of the charcoal's surface.

The study concludes that combining these two methods offers a powerful, circular solution for water treatment. The living plant can be used to clean large volumes of water over time, and once it has served its purpose, it can be converted into a highly efficient filter material to polish the water further or treat new batches. This approach turns a waste product into a valuable resource, maximizing the utility of the biomass. The researchers found that while the living plant is excellent for slow, large-scale cleanup, the biochar is superior for rapid, high-efficiency removal. By using the same plant for both roles, the method minimizes waste and provides a cost-effective strategy that could be particularly useful in regions where industrial pollution is high but advanced treatment infrastructure is lacking. This dual use of nature's own materials suggests a path toward cleaner water that is both environmentally friendly and economically feasible.