Westernport Water, a wastewater utility in Phillip Island, Victoria, is transforming a wastewater lagoon into a plant-filled wetland to explore how Australian native wetland plant species can improve water quality, reduce greenhouse gas emissions and manage emerging contaminants such as per-and polyfluoroalkyl substances (PFAS). This two-year research project commenced in 2023 and involves the installation of a constructed floating wetland (CFW) system on a wastewater lagoon at the Cowes Wastewater Treatment Plant. It is anticipated that early results will be available in 2024. The project is the first field-scale study looking at how nature-based solutions can be used to reduce greenhouse gas emissions from wastewater treatment plants while simultaneously acting to remove contaminants and improve water quality. While this study is focused on wastewater, the outcomes will inform and benefit similar projects in a broad range of sectors including stormwater management as emerging contaminants and excessive nutrient loading are not issues exclusive to wastewater.
Constructed floating wetlands, which are also called floating treatment wetlands, free-floating wetlands or artificial floating islands, are a relatively novel nature-based water treatment technology that has seen a sharp increase in adoption during the last 20 years.1 CFWs have been used for both stormwater and wastewater treatment, as well as for provision of habitat and for aesthetic enhancement.2
Constructed floating wetlands are designed to mimic the functions and appearance of natural floating islands but are designed to provide enhanced treatment functions. These functions are similar to traditional constructed wetland systems, but also have the treatment attributes typically associated with a pond/lagoon system. A buoyant structure supports the growth of plants on the structure’s surface, with the root mass growing directly into the water column, similar to a hydroponic system. The plant roots utilise nutrients within the water column to increase biomass. The root mass also provides a significant surface area that is colonised by microbial biofilm. These biofilms are microorganisms that sequester and remove nutrients through adsorption, absorption and phytodepuration. A significant benefit of CFWs is that they can be retrofitted into existing waterbodies, require no additional land area and do not take up any flood storage volume because they float on the water surface.
A 330-m(3,552-foot) CFW system was installed at the Cowes Wastewater Treatment Lagoon2 in April 2023, following background monitoring of the system to determine baseline values regarding emissions and nutrient concentrations (Figure 1).
A detailed record of water quality data was provided by Westernport Water to better characterize the typical water quality attributes of this system. Following the installation, monitoring of nutrients, emerging contaminants and greenhouse gas emissions commenced. The system is monitored at the start and end of the CFW system, with a paired control established adjacent to the system so the performance can be characterized (Figure 2). Presently, the constructed floating wetland is in the plant establishment phase, with 900 individual plants of Phragmites australis (common reed) and 900 plants of Baumea articulata (jointed rush) being monitored for shoot and root development monthly.
Research by Deakin University’s Blue Carbon Lab documented that a direct link exists between dissolved nutrient concentrations and greenhouse gas emissions, specifically methane. Based on data from smaller systems, reducing total nitrogen and phosphorus leads to a disproportionately higher reduction in average methane emissions.3,4 As the plants utilise nitrate to grow, we hypothesise that lower nutrient concentrations will reduce methane emissions from the wastewater lagoon. Further, the plant species utilised in this study can be harvested.
A similar study5 in Queensland, Australia, showed that harvesting Baumea articulata shoots can remove approximately 104 and 13 g/m of nitrogen and phosphorus, respectively (0.02 and 0.003 pound/foot).2
In relation to emerging contaminants, recent research by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) has demonstrated that both Phragmites australis and Baumea articulata uptake and sequester two PFAS, namely perfluorooctanoic acid and perfluorooctane sulfonic acid.6 Though these substances are commonly found in wastewater and stormwater at very low concentrations (ng/L levels), PFAS present an emerging problem for wastewater utilities because wastewater treatment plants have difficulty removing these contaminants. Constructed floating wetlands have the potential to offer a low-cost, simple method to remove such pollutants via plant uptake and harvesting. The harvested material can then potentially be converted into biochar/activated carbon via pyrolysis, which destroys the PFAS.
This project is a collaborative partnership between Westernport Water, Deakin University (Blue Carbon Lab), Covey Associates Pty Ltd, Clarity Aquatic and the CSIRO. Westernport Water staff is supporting scientists from Deakin University and CSIRO to assess the effectiveness of the floating wetland plants in removing dissolved nutrients and emerging contaminants from treated wastewater. Assessments also evaluate how well the system functions at both improving water quality and reducing greenhouse gas emissions.
This technology does help organizations achieve sustainability goals in several ways. Greenhouse gas emissions are reduced through nature-based solutions on existing infrastructure. By expanding the capacity or extending the length of time before expansion is needed, floating wetland systems can eliminate or defer the need to build new infrastructure. Further, the floating wetland system utilised in this project is 100% recyclable and the plant material will be harvested and composted for the purpose of land management projects where possible, or potentially converted into materials such as biochar which will have a further potential use for water quality improvement.
References:
- J. Ayres, J. Awad, C. Walker, D. Page, J. van Leeuwen, S. Beecham, Constructed Floating Wetlands for the Treatment of Surface Waters and Industrial Wastewaters, in: N. Pachova, P. Velasco, A. Torrens, V. Jegatheesan (Eds.), Regional Perspectives of Nature-based Solutions for Water: Benefits and Challenges, Springer International Publishing, Cham, 2022, pp. 35-66. https://doi.org/10.1007/978-3-031-18412-3_3.
- Lucke, T., Walker, C., Beecham, S., Experimental designs of field-based constructed floating wetland studies: A review. Sci. Total Environ., 2019 660, 199–208.
- Malerba, M.E., Lindenmayer, D.B., Scheele, B.C0, Waryszak, P., Yilmaz, I.N., Schuster, L., Macreadie, P,I. Fencing farm dams to exclude livestock halves methane emissions and improves water quality. Glob. Chang. Biol. 2022; 28: 4701-4712.
- Ollivier QR, Maher DT, Pitfield C, Macreadie PI. Punching above their weight: Large release of greenhouse gases from small agricultural dams. Glob. Chang. Biol. 2019; 25: 721-732.
- Huth, I. Walker, C. Kulkarni, R. and Lucke, T. Using Constructed Floating Wetlands to Remove Nutrients from a Waste Stabilization Pond. Water, 2021, 13, 1746. https://doi.org/10.3390/w13131746.
- J. Awad, G. Hewa, B.R. Myers, C. Walker, T. Lucke, B. Akyol, X. Duan, Investigation of the potential of native wetland plants for removal of nutrients from synthetic stormwater and domestic wastewater, Ecological Engineering 179 (2022) 106642. https://doi.org/10.1016/j.ecoleng.2022.106642.
About the Experts
Christopher Walker, BEnvSc., BSc (Hons), Ph.D., CPESC, is an associate and manager of the Water, Environment & Bushfire divisions at Covey Associates Pty Ltd., Maroochydore, Queensland, Australia.
John Awad, BSCE (Hons), MSCE, Ph.D., is a research engineer at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in South Australia, Australia.
Martino Malerba, BSc, BSc (Hons), Ph.D., is an Australian Research Council Discovery Early Career Research Award Fellow at the Blue Carbon Lab, Deakin University, Melbourne, Victoria, Australia.
Lukas Schuster, BSc, MSc, Ph.D., is a postdoctoral research fellow at the Blue Carbon Lab.
Terry Lucke, Ph.D., FIEAust, CPEng, RPEQ, EngExec, NER, is a senior civil and environmental engineer at Covey Associates Pty Ltd.
Divina Navarro, Ph.D., is a research scientist at CSIRO.
Ilse Hall, BSoc.Sc, DipPM, is a project officer at Westernport Water, Newhaven, Victoria, Australia.
Melinda Glew, BSc, is a climate change and environment advisor at Westernport Water.
Meg Humphrys, BSc (Hons), is a liveability communities advisor, Water Services Association Australia.
