Rooting Out Pollution: A Natural Floating Wetland for Heavy Metal, Nutrients, and PFAS Remediation

Transcript:

Hello, my name is Cynthia Rayson and my project is rooting out pollution, a natural floating wetland for heavy metals, nutrients, and PFAS remediation.

Clean water should not be a privilege. Yet, communities across Canada struggle with unsafe and polluted water with 73% of Indigenous water systems labeled as medium or high risk. Traditional treatment methods fall short of emerging contaminants and are expensive using harsh chemical materials. To combat this, I developed an all natural floating wetland prototype.

My system utilizes phytoremediation using plants to clean water naturally. It also employs the use of three different Indigenous wetland plants that have been long recognized for their remedial properties, drawing on traditional ecological knowledge to support more effective environmental restoration.

My prototype was effective in eliminating traditional contaminants such as heavy metals, nutrients, and cyanobacteria, but was also effective in eliminating PFAS, an emerging contaminant known as “forever chemicals”, which are especially difficult to remove, thus protecting ecosystems and creating safer water for communities.

Water contaminants such as heavy metals, excess nutrients, and cyanobacteria threaten our aquatic ecosystems and human health. Specifically, these pollutants destroy biodiversity and are linked to numerous human health concerns. Recently, an illusive and deadly chemical has come to light: PFAS. Approximately 98.5% of Canadians have detectable levels of per- and polyfluoroalkyl substances (PFAS) in their blood. PFAS is virtually everywhere, in our drinking water, textiles, electronics, soil, and more. PFAS exposure has been linked to cancer, infertility, delayed child development, reduced immune response, and more.

We need a solution to all this pollution: phytoremediation could be the answer. Phytoremediation uses naturally occurring plants to remove pollutants from the environment. Essentially, plant roots absorb the pollutants and convert them to less harmful substances.

A typical way to introduce phytoremediation to an ecosystem is a floating wetland system. A floating wetland system is an artificial, buoyant platform that allows aquatic plant roots to grow in deep water. However, common commercial systems are made from plastics, chemically treated wood, and wire that can inhibit plant growth and contribute to water pollution.

My nature-based solution uses native birch wood and local wetland plants that are readily available and easily scalable into larger systems, but more importantly do not give rise to further contamination. Typical systems target one contaminant, but my project draws on traditional Indigenous knowledge to support ecological restoration using an innovative floating wetland protype to tackle a diverse group of pollutants simultaneously using native plants to solve local issues.

Carex lupulina (Hop Sedge) and Iris versicolour (Blue Flag Iris) are hyperaccumulating plants with fibrous root systems that can penetrate contaminated sediments, offering a large surface area for absorbing metals. As deep rooted wetland plants, they have potential to filter and sequester PFAS.

Additionally, plants degrade pollutants through rhizofiltration, immobilizing and breaking down substances using enzymes in their roots; rhizospheric biofilms play a key role during this process. Lemna minor (Duckweed) are considered “biological sponges” for contaminants and can adapt to harsh environments.

I also included a homemade barley-biochar-filter. Barley-straw is known to inhibit algae growth, releasing acids as it decays, forming hydrogen peroxide. Biochar acts like a sponge, using its surface area and porous framework to physically entrap PFAS molecules. Activated biochar also contains both cations and anions that attract various contaminants.

In Phase 1, each remediation material was placed in a cup with 200 mL of spiked pollutant solution individually. This was done in triplicates for each pollutant for a total of 66 cups.

In Phase 2, the 4 remediation materials were put together in a wooden prototype, then placed in a bin with 1600 mL of spiked pollutant solution. This series was run in triplicates for a total of 18 prototypes with the addition of two new contaminants: a combination of all pollutants, and a pond sample.

Pollutant concentration was measured at the beginning and end of the 3 week period. Ion chromatography was run to identify PFAS materials and nutrients. X-Ray Fluorescence was run to identify metals. And UV-Vis spectroscopy and a hemocytometer cell count was performed to measure cyanobacteria. Dissolved oxygen, pH and plant health was also monitored.

In Phase 3, three prototypes were left in a local pond for a week to see if they could endure a natural setting.

In the heavy metal tests, remediation materials were tested for their ability to remove copper from water. The best performing material was Carex lupulina, remediating 94% of the copper. Additionally, the prototype sequestered 81% of the copper when by itself. In combination with other pollutants, the prototype was capable of remediating 75% copper. In the pond sample, the prototype removed 74% of the heavy metal. This data was over a 3 week period, but I hypothesize that remediation could be increased over a larger time span.

In the nutrients tests, the barley-straw-biochar-filter was the most successful at removing nitrates, while Carex lupulina was most successful in removing phosphates. The prototype notably remediated 55% of nitrates and 86% of phosphates. In combination, the prototype was successful in removing 75% of nitrates and 42% of phosphates. In the pond sample, the prototype removed 80% of nitrates and 91% of phosphates.

In the cyanobacteria tests, the most effective remediation material was the barley-straw-biochar-filter with a 0% algae growth increase. This was followed by Carex lupulina which showed prominent success in inhibiting algae growth. The prototypes were successful in limiting algal growth with an 11% cell culture and 500% UV pigment absorption increase in comparison to the control which had 1700% cell culture growth and 3567% UV pigment absorption increase. The combination and pond prototypes were also successful in significantly reducing cyanobacteria growth in comparison to the controls.

Finally, in the PFAS series, the most effective remediation materials were Lemna minor and Iris versicolour with 89% and 81% pollutant removal respectively. The prototype was successful in remediating up to 40% of PFAS. In combination with other pollutants, the prototype was effective in sequestering 30% of PFAS. In the pond sample, the prototype remediated 15% of PFAS.

The plant height and weight monitoring demonstrates that plant health was not deterred by pollutants, and plants can remain healthy while remediating contaminants. Additionally, water quality testing for pH and dissolved oxygen emphasizes water health during phytoremediation.

The prototypes tested during Phase 3 were successful in enduring the natural environment for a full week without destruction, including surviving several rain storms. The use of "pitch" ensured the longevity of the prototypes and prevented them from decomposing in the natural environment.

An analysis of PFAS chemicals in the spiking solution was performed at the University of Waterloo using liquid chromatography-mass spectrometry. Figure 9 shows the PFAS chemicals present in the solution.

An ordinary one-way ANOVA was performed on the results from Phases 1 and 2. The test highlights the statistical significance of each remediation material and shows how pollutant levels most definitely vary based on material. All samples from the heavy metals, nitrate, phosphate, and PFAS tables showed statistical significance to the control, demonstrating pollutant remediation. More than that, each table demonstrated statistical significance overall, so I was able to reject my null hypothesis that pollutant concentration would not change in the presence of a prototype or remediation material. Figure 10 shows the statistical summaries for each data set.

Phytoremediation is more environmentally friendly and cost efficient due to the inexpensive and abundant nature of plants, and is simpler than traditional pollutant removal methods such as chemical precipitation. Commercially available floating wetlands use plastics, wire, and pressure treated lumber that introduce pollutants and dangers to the water. Additionally, my natural floating wetland prototype costs $8.25 per square foot in comparison to commercial products that start at $46 per square foot.

Previous research and this experiment have shown that floating wetlands can remediate heavy metals and nutrients. However, I set out to create a natural system that not only targeted excess nutrients and metals simultaneously but also PFAS. PFAS remediation through wetlands has been scarcely studied worldwide, and has yet to be studied in Canada, however my research suggests that phytoremediation is a plausible solution to PFAS pollution, sequestering up to 40% of PFAS.

Furthermore, First Nations Reserves often face the most significant water quality issues and specifically have PFAS levels up to 21 times higher than the general Canadian population. These Reserves are often found on water bodies and could greatly benefit from my cost effective and environmentally friendly floating wetland prototype.

Water is an invaluable resource. Why would communities pay for expensive commercial systems when local wood is free and carefully selected native plants can remediate our most prevalent pollutants including PFAS? In summary, this research demonstrates that my all natural floating wetland prototype can serve as an environmental and cost efficient alternative to root out pollution.

Next Steps:

1. Test using larger Duckweed species (Spirodela polyrrhiza).

2. Test using larger chunk biochar.

3. Test using real PFAS materials (defined chains).

4. Test to remediate oil.

Sources of Error:

1. Biochar was very fine and leaked out of the filter.

2. Lemna minor (Duckweed) species was very small and washed out of hydroponic cup easily during the storm.

3. Use of a more sensitive balance would have led to more accuracy when spiking solutions.

I would like to thank the Aitken family for allowing me to use their property for my in-situ experiments. Thank you to my high school principal, Daniella Mancusi, for her support and help getting in contact with my mentors. I would also like to thank Lambton College for allowing me to use their greenhouse and labs for the duration of my project. Most of all, I would like to thank my incredible mentors from Lambton College: Kurtis Tamming, Cesar Gallegos Rios, Daniel Nienhuis, and Gabriel Grau for all their guidance and assistance. Another thanks goes to my mentor Aaron Plain from the Maajiigin Gumig Greenhouse for his guidance and support with the wetland plants. Additionally, I would like to thank my mentors from the University of Waterloo: Emir Nazdrajić and Dr. Scott Hopkins for their help with PFAS testing. Finally, I would like to thank my family for their support.

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