From the Florida Everglades to the Hudson Bay Lowlands, the swamps, bogs, bayous and wetlands of the world cover 6% of Earth’s surface — yet are home to a good 40% of our plant and animal species. They also act as the Earth’s kidneys, in a way: filtering out pollutants, sequestering carbon, and otherwise purifying and holding much of the planet’s fresh water.
For our everyday use, however, chances are your drains and sewers lead to a wastewater treatment plant for that filtration… a necessary cleaning site, not exactly known for their air quality.
Dr. Lukas Schuster at Australia’s RMIT University says wastewater treatment plants “actually emit quite a lot of methane and nitrous oxide” — and those two greenhouse gases are, respectively, 30 times and 270 times more potent than carbon dioxide is. “People don’t really think about that. They think about the wastewater treatment, like the dirty water goes in, the clean water goes out, and that’s it — but they never think about the emissions that actually come from this treatment. ”
Nutrient loads are the drivers of those wastewater emissions. “The more nutrients you have,” Dr. Schuster explains, “the more activity you have from the microbes that are converting or taking up those nutrients, and they are emitting those greenhouse gases.”
Some wastewater treatment plants have been using constructed floating wetlands, or CFWs, for a few decades now, with the idea of adding a more natural filter into the system: “It’s known that the floating wetlands can take up nutrients and pollutants from those water bodies, but it has never been tested before in terms of emission reductions.”
Never been tested, that is, until Dr. Schuster and crew came along. They set up a monitoring station at a CFW on Phillip Island near Melbourne, Australia, where treatment plants are expected to reach “net zero” emissions by 2030. A control channel was also monitored to directly compare the emission reduction within the lagoon.
After a 2-year study, it became clear that CFWs were a worthy opponent for those greenhouse gas molecules: “We found a 20% to 30% reduction in carbon dioxide, a 30 to 60% reduction in methane emissions, and an 18% reduction in nitrous oxide emissions; it was quite significant.”
You might think deploying these artificial platforms would be costly, but Dr. Schuster says it’s actually a cheaper and more efficient option compared to upgrading the wastewater lagoons — to say nothing of the biodiversity benefits. “It’s providing some more habitat in urbanized lagoons,” Dr. Schuster offers, “like in urban settings, we put in some green, some plants and then the birds will love it, for example.”
Dr. Schuster says his team and the treatment plant officials were very pleased with the results, with plans to work these wetlands into other facilities in the future: “It will be interesting to see how that actually scales up to like bigger lagoons or bigger surface areas… but it’s definitely a very promising pilot study that we did, that we found some really incredible results.”
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