Wastewater treatment plants are an essential part of modern life — but they also produce greenhouse gases such as carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). These emissions account for a notable share of the water sector’s carbon footprint, with methane and nitrous oxide being especially potent contributors to global warming.
As part of Victoria’s goal to achieve net-zero emissions by 2035, Westernport Water partnered with RMIT University’s Centre for Nature Positive Solutions to investigate innovative, nature-based approaches to lowering emissions from wastewater lagoons. The focus: whether a simple intervention, a constructed floating wetland (CFW) could make a measurable difference in reducing greenhouse gases.
In May 2023, a pilot floating wetland was installed in a wastewater effluent storage lagoon. The lagoon was divided into two channels: one fitted with the floating wetland and one left as a control. The floating structure was planted with wetland species, including Phragmites australis, Baumea articulata, and Bolboschoenus caldwellii. Over two years, researchers continuously monitored greenhouse gas fluxes with floating “Pondi” sensors, while also testing water quality and plant nutrient levels each month.
What the study found
The results, released in April 2025, were striking. While nutrient concentrations such as nitrogen and phosphorus did not differ significantly between the control and treatment channels, greenhouse gas emissions told a different story:
- Carbon dioxide (CO₂): 30% lower in the treatment channel.
- Methane (CH₄): 63% lower at the start of the channel and 39% lower at the end.
- Nitrous oxide (N₂O): 17% lower at the channel end.
In short, the wetland substantially reduced greenhouse gas emissions but did not record a reduction in nutrients. Researchers suggest that microbial communities on the plant roots, alongside higher dissolved oxygen levels supporting methane oxidation, are likely driving these reductions.
Why it matters
For utilities like Westernport Water, these findings offer a practical pathway to reduce emissions from effluent storage lagoons, a notoriously hard-to-abate source. Unlike mechanical aeration or advanced treatment upgrades, floating wetlands are comparatively low-cost, passive systems that can deliver measurable benefits with minimal energy use.
The benefits may also extend beyond climate. Constructed wetlands provide habitat for local biodiversity and have the potential to help filter emerging contaminants such as PFAS and pharmaceuticals. As such, they represent a multi-benefit, nature-based tool for water corporations seeking both climate and environmental gains.
Next steps
The pilot highlights promising results but also points to areas for refinement. Larger wetland coverage and longer hydraulic retention times may improve nutrient uptake, and operational lessons, such as managing temporary methane spikes after plant harvesting — will inform any future scale-up. Longer-term monitoring and trials in different lagoon types will be important to confirm and extend these results.
Building on this, Westernport Water (Dr. Kavindra Paranage, Ms. Tamika Johnston) is working closely with the RMIT team, comprising Dr. Martino Malerba, Dr. Stacey Trevathan-Tackett, and Dr. Lukas Schuster — to continue investigating how floating wetlands and other nature-based approaches can cut emissions and strengthen resilience across the Victorian water sector.
