Floating wetlands could offer a practical way to reduce emissions from wastewater treatment, after a world-first two-year trial in Australia found that floating platforms planted with native vegetation cut greenhouse gas emissions from a wastewater lagoon by more than a quarter. Conducted by RMIT University, Westernport Water and CSIRO on Phillip Island, the trial recorded reductions of up to 36% in CO₂ emissions, 66% in methane and 18% in nitrogen emissions compared with a lagoon without a floating wetland.

The findings are significant because wastewater treatment contributes around 1.6% of human-induced greenhouse gas emissions globally, while water utilities have relatively few scalable options for reducing those emissions. The research, published in the Journal of Environmental Management, suggests that supporting naturally occurring microbial communities around plant roots could provide an emissions-reduction route without requiring major high-tech infrastructure changes.

How the Floating Wetland Reduced Emissions

The trial used a floating platform measuring 330 square metres, roughly the size of one-and-a-half tennis courts. Native reeds and sedges were planted across the platform, with their roots extending directly into the wastewater below.

Those submerged root systems created habitats for microbial communities that consume nutrients and pollutants. Researchers found that measurable emissions reductions became apparent about four months after the wetland was installed. The lagoon’s emissions were then continuously monitored for two years, allowing the researchers to compare it with a control lagoon that had no floating platform.

RMIT’s Dr Lukas Schuster said the study provides the first evidence at this operational scale that microbial communities supported by wetland plant roots can reduce wastewater emissions without relying on high-tech solutions.

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Why the Approach Could Be Scalable

• One of the most important aspects of the trial is that floating wetlands can potentially be retrofitted into existing wastewater lagoons.
• That means utilities may be able to introduce the technology without completely rebuilding their treatment infrastructure.
• Westernport Water Managing Director Dona Tantirimudalige said the results provide a foundation for testing the approach across different lagoon designs and operating conditions.
• The technology is also being developed through CSIRO’s nature-based solutions program.
• Beyond emissions, the floating platforms can help remove contaminants and improve water quality before treated water reaches downstream ecosystems.
• That combination could make the approach more attractive to water utilities looking for environmental benefits beyond carbon reduction.

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From Wastewater Lagoons to Farm Ponds

The Australian research is now moving into another setting. RMIT researchers, working with Melbourne Water and the Bass Coast Landcare Network, are testing floating wetlands in farm ponds across the Bass Coast.

The new trial is examining whether the systems can improve water quality and biodiversity while also reducing emissions. Australia has an estimated 1.8 million farm ponds, creating a potentially large application area if the technology performs successfully.

The wastewater trial does not establish that every lagoon will achieve the same reductions, and researchers say further testing is needed under different conditions. But the results provide a promising starting point: instead of treating wastewater infrastructure only as a source of emissions, floating plant systems could help turn existing lagoons into part of the climate solution.

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