Creating new wastewater infrastructure is often time consuming and expensive, but when an area is increasing in population, is it often essential. One approach to increasing the performance of wastewater treatment assets, and avoiding many of the costs of increasing wastewater infrastructure footprints, is using nature-based solutions such as floating wetlands.
Queensland based consultancy, Covey Associates, has been a leader in developing floating wetland projects in Australia and internationally over the last 15 years. They have recently implemented some highly successful projects with utility TasWater, who wanted to explore whether non-traditional solutions could provide similar outcomes to expensive mechanical upgrades.
The solution presents as a simpler and cheaper alternative to traditional approaches such as constructing additional wastewater lagoons or expanding the storage of existing ones which can require extensive capital expenditure.
Dr Chris Walker, a director and principal at Covey is an environmental and civil engineer and scientist, says that the floating wetlands can not only make existing wastewater systems such as lagoons, more efficient, but also may be able to assist to reduce greenhouse gas emissions.
“TasWater funded a full-scale trial at three different sites looking at how these floating wetlands can enhance the performance of their existing systems, with a specific goal of having a reduction to nutrients levels in their effluent by an additional 40% to 60% in line with what they have seen historically,” said Walker.
“We’re about a year into this process and we’ve had really rapid biomass accumulation of the plant mass over the Tasmanian summer, which we didn’t expect.
“We then harvested that plant mass as an initial assessment, and what is interesting is that the plant removal can account for as little as 30% of the overall performance. The remaining performance can be from microbial activity because the floating wetland is basically creating a habitat for microbes to act as a catalyst for nutrient processing.”
The floating wetlands are constructed floating structures with a choice of appropriate vegetation which mimic natural ecosystems and their processes. Plants grow into the water column similar to hydroponics, where they then enhance sedimentation through disrupting water flows.
A commonly used plant is Phragmites australis, which is used in the remediation of wetlands around the world and is a “known powerhouse” in breaking down and removing pollutants. The high surface area of the roots encourages microbial biofilm growth, and the biofilm in turn removes finer particles and plays a role in nutrient transformation.
The floating wetlands are easily retrofitted onto lagoons, and allow easy maintenance access and caters to fluctuations in water levels. They require no power, and improve water quality through pollutant uptake and microbial activity.
At a cost of $2 million for the three projects at TasWater, the floating wetlands are also extremely cost effective.
TasWater Operational Improvement Manager Anthony Allan said the pilot program brings the organisation closer to achieving its goal of zero nutrient discharge by 2050.
“The floating wetlands trial is a key component of TasWater’s long-term strategy to explore nature-based, energy-efficient solutions for wastewater management,” Mr Allan said.
“Not only do these wetlands support wastewater treatment, but they also enhance local biodiversity by providing habitats for insects and birds.”
Chris Walker says Covey Associates also worked with the CSIRO, Westernport Water, the RMIT University’s Centre for Nature Positive Solutions and Clarity Aquatic on another project in Victoria.
This two-year pilot project involved the installation of a floating wetland system on a wastewater lagoon at the Cowes Wastewater Treatment plant on Philip Island.
“Through this project we found we had a reduction of CO2 emissions by 30% and methane by 63%, and methane has a significantly greater impact than CO2,” said Walker.
“We also had a 17% reduction in nitrous oxide gases through the wetland, and we were able to measure this as we had a control project running which enables us to compare.”
While the floating wetlands are proving effective in the management of wastewater, they can also be used in more aesthetic ways in urban projects.
Covey Associates were not involved in the project but Chris Walker points to the Wild Mile project in Chicago, which is called the “world’s first ever floating eco-park.”
Constructed as an industrial corridor for lumber and coal barges in the 19th century, the area has been transformed since 2017 into a recreation park which is also used for education, research and community gatherings.
The floating wetlands in the project mimic a natural wetland ecosystem and riparian vegetation which existed in the Chicago region before the city was developed, making a positive contribution to water quality and to the aesthetics and community amenity of the area.
“The floating wetlands have re-naturalised this section of Chicago River without cost of removing the heavily engineered revetment walls,” said Walker.
“It’s a way to bolt on a naturalised solution without the huge costs associated with reconstruction.”
Dr Chris Walker and Anthony Allan will be presenting the TasWater case study as part of the Sustainability Stream at IPWC 2025, to be held at ICC Sydney from 25-28 of August.
