Floating wetlands made from trash help clean up polluted lakes

Once Pradhanan found a trash mixture that could be fashioned into platforms and would withstand degradation over time, he began discussing it with his Nepali colleagues, and by 2021 they had secured $78,000 in funding from the Asia-Pacific Network for Global Change Research, a research and policy funding organization, to conduct research in Nepal, India and Bangladesh.

Although Nagdaha and other lakes in India and Bangladesh do not provide drinking water to their inhabitants, they do have cultural and religious significance. Pradhanan has visited Nepal many times and seen children swimming in Nagdaha’s murky waters, dogs licking water from the shore, and women sitting on the shore washing dishes and clothes. Pradhanan and Small Earth Nepal wanted to clean the lake and beautify it at the same time. They chose a flowering plant that would serve both purposes: the Indian shot.Canna indica) and Scarlet Sage (Salvia splendensThe bright red flowers of the () stand out against the gray water surface.

After installing the floating platform in fall 2022, the researchers tested the water monthly with results consistent with their expectations. Laboratory TestingNitrate levels were reduced by 99 percent, phosphates by 80 percent, iron by 56 percent, and ammonia by 55 percent. Dissolved oxygen levels increased by half. The results were: Journal of Civil Engineering For review.

Growing flowering plants adds aesthetic value to the water body, but the collaborative avoids growing food on the platforms because plants accumulate high concentrations of pollutants. But it’s not just humans who are intrigued by the floating wetlands: geese and ducks flock to the mats, sit on the platforms and dump their phosphorus-rich waste into the water.

Pradhanan came up with an ingenious solution to the mischievous mallards: he tied silver ribbons to the plant’s stems, whose sharp light would scare the birds away. While the scientists don’t want geese at the FTWS, ​​they would love to see pollinators like bees and songbirds, as well as the diverse microbes that live in the plant’s roots and get their energy from digesting pollutants in the water.

“Floating wetlands really are a case of ‘if you build it, they will come,'” says Max Rome, who did his doctorate on floating wetlands on Boston’s Charles River and now works for the Charles River Watershed Association. “These systems are very effective at creating wetland biodiversity in places where there’s no room for wetlands.”

While waste-based systems solve some of the water pollution problems, other issues remain, such as microplastics. Incorporating local waste into the mats shouldn’t make things worse overall, since much of the waste was collected from the water in the first place. But the high plastic content in the water means that even after cleanup, there may still be health risks for local residents.

While Pradhanan and outside researchers have expressed concerns about incorporating Styrofoam and other plastics into a trash-based FTWS, ​​they say the mats’ benefits generally outweigh the costs. “If we can take waste materials that would normally be in the water and make a product that actually helps purify the water, that’s great,” White says.