Wastewater contains the byproducts of our lives: excess nutrients that swirl down the drain and end up in treatment facilities. To reuse this water safely, these contaminants must be broken down—a process that releases potent greenhouse gases. Now, researchers have found a way to clean water with fewer emissions: portable wetlands. A recent preprint on EarthArXiv shows floating platforms covered in wetland plants helped reduce water pollution and even lowered greenhouse gas emissions at a wastewater site in Australia.

“In some ways it’s really complicated, but actually in other ways it’s really simple,” says Ellen Nisbet, a microbiologist at the University of Nottingham who was not involved in the study. “You don’t need a huge, very expensive facility to deal with this. You just need to grow some plants.”

Human activities cause nutrients including phosphorus and nitrogen to build up in wastewater. To make this water safe for dumping into the ocean or reusing for irrigation, it must be decontaminated, usually by microbes. The catch is that as they dine on the water’s nutrients, these microorganisms release 1.6% of all human-driven greenhouse gas emissions.

The “eye-opening” thing about this statistic, says Lukas Schuster, an environmental scientist at the Royal Melbourne Institute of Technology and lead author of the study, is that this microbial breakdown accounts for 7% to 10% of global emissions of methane and nitrous oxide, which have far higher heat-trapping potential than carbon dioxide, in the short term. But microbes aren’t the only way to treat wastewater—wetlands work, too. Floating wetland plants, with roots growing in the water, can remove pollutants by physically trapping debris and directly absorbing nutrients through their roots and leaves.

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