Phytoremediation: Floating Treatment Wetlands
Ann Jeline Manabat, MPH: Health Promotion Track
Our waterways are being starved of life through pollution
Many industrial units discharge pollutants and contaminants into the environment without treatment.
Aquatic ecosystems, particularly freshwater ecosystems, are polluted through the outcome of human activities such as urbanization, industrialization, and agricultural activities (Bashir et al., 2020).
The accumulation of utilized pesticides, fertilizers, and sewage from residential and industrial sectors eventually ends up in the aquatic environment (Bashir et al., 2020).
According to the Environmental Protection Agency's (EPA) most current national water quality surveys, over half of our rivers and streams, as well as more than a third of our lakes, are contaminated and unsafe for swimming, fishing, or drinking. The most common type of contamination in these freshwater sources is nutrient pollution, which includes nitrates and phosphates.
Lakes, rivers, streams, reservoirs, and ponds emit large amounts of carbon dioxide and methane. The emissions of these greenhouse gases diffuse from the water's surface and are large enough to contribute to climate change (Peacock et al., 2019).
When the quality of water deteriorates, this can lead to the spread of infectious diseases, alter the functioning of ecosystems, and contaminate the food chain.
Photo by Ariungoo Batzorig on Unsplash
Impact on human health
Nitrogen and phosphorous are nutrients that are natural parts of aquatic ecosystems, however, high concentrations of these nutrients in water bodies can have diverse and far-reaching impacts on human health. An increase of these nutrients in our bodies of water cause algae to grow, and has negative impacts on our water quality, food resources, and habitats, as well as reducing the oxygen available to our fish and aquatic life.
Algal blooms are huge growths of algae that can limit or eliminate oxygen in the water (EPA, 2021), causing diseases and death in large numbers of fish. Some algal blooms are detrimental to humans because they create high levels of toxins and bacterial growth. An individual is highly susceptible to disease if they come into contact with polluted water, consume affected fish/shellfish, or drink contaminated water.
List of Potential Health Risks
Liver Damage
Thyroid Disease
Decreased Fertility
High Cholesterol
Obesity
Hormone Suppression
Cancer
Damage to the gastrointestinal tract, nervous system, and kidneys
Transmission of diseases such as diarrhoea, cholera, dysentery, typhoid, and polio
Who is most impacted by water pollution?
While water contamination is known to be a global issue, there are certain populations that are much more vulnerable than others. Large numbers of illnesses and death are a result of water pollution, and the communities that are disproportionately affected are communities of color, low-income communities, and communities that do not have access to adequate housing and transportation options. Children and pregnant mothers are most susceptible to disease from water contamination as well.
Public Health and Policy
Due to increasing public concern for the environment and condition of the waters, the Environmental Protection Agency (EPA) established the Clean Water Act in 1972 to restore and maintain clean and healthy waters. The amendment:
regulated pollution discharge into the waters of the United States,
gave EPA the ability to implement pollution control measures, such as setting wastewater regulations for industries,
established rules for water quality standards for all pollutants in surface waterways,
and made it illegal to dump any pollution into navigable waters from a point source unless a permit was secured under its rules.
The Safe Drinking Water Act was established shortly after in 1974 to protect the quality of drinking water in the U.S. The act:
authorized EPA to establish minimum standards to protect tap water and requires all owners or operators of public water systems to comply with these health-related standards
required a detailed risk and cost assessment
established standards for state programs to protect underground sources of drinking water from endangerment by underground injection of fluids
Environmental Justice Issues
Despite EPA's efforts for cleaner water, the lived experiences of people of color continue to shed light on ongoing water contamination to this present day. An infamous example is the recent lead-contaminated water crisis in Flint, Michigan, with 40% of the residents being mostly low-income and 56% of the population being Black (Denchak, 2021). As a result, children in Flint had doubled and even tripled incidences of elevated blood lead levels.
This has sparked broader racial and socioeconomic disparities in exposures to drinking water and contaminants. In relation to this:
Low-income communities are more likely than their wealthier counterparts to be served poor-quality drinking water with greater levels of potentially hazardous pollutants (Uche et. al., 2021)
Smaller drinking water systems tend to have higher arsenic levels in drinking water (Uche et. al., 2021)
Current Status Based on the Assessment of National Rivers and Streams
To determine water quality conditions, EPA compared sampling results to national benchmarks (2013-2014). These benchmarks draw from conditions represented by a set of least-disturbed (or reference) sites in each of the nine different ecoregions.
Waters scoring “good” had indicator values as good as the best 75 percent of the distribution of reference sites in an ecoregion.
Waters scoring “poor” had indicator values worse than 95 percent of the distribution of reference sites in an ecoregion.
Waters scoring “fair” had indicator values in between the “good” and “poor” categories.
Biological Indicators
Chemical Indicators
NRSA reports on four chemical stressors:
Total Phosphorous
Total Nitrogen
Salinity
Acidification
Findings:
43% (522,796 miles) were rated poor for nitrogen
58% (706,754 miles) were rated poor for phosphorous
Poor biological condition based on bottom-dweller macroinvertebrates was almost twice as likely in rivers and stream miles rated poor for nutrients.
Photo by Louis Reed on UnsplashPhysical Habitat Indicators
Four indicators of physical habitat were assessed:
Least-disturbed reference sites’ in‐stream fish habitat
Streambed excess fine sediments
Riparian vegetative cover (vegetation in the land corridor surrounding the river or stream)
Riparian disturbance (human activities near the river or stream) was scored based on number and proximity of features such as roads and buildings.
Findings:
64% (778,585 miles) of river and stream miles were rated good for in-stream fish habitat
58% (701,763 miles) of river and stream miles had good ratings for riparian vegetation
52% (627,829 miles) scored good for streambed sediment levels.
Bottom-dweller macroinvertebrate condition was almost twice as likely to be rated poor when sediment levels were rated poor than when they were rated fair or good.
Photo by Joshua J. Cotten on UnsplashHuman Health Indicators
Three indicators of potential risks to human health were assessed:
Enterococci (bacteria that indicate fecal contamination)
Microcystins (naturally occurring algal toxins)
Contaminants in fish tissue (mercury, polychlorinated bipenyls or PCBs, certain per- and polyfluoroalkyl substances or PFAS)
Findings:
69% (833,529 miles) of rivers and stream miles contain enterococci, which are below the EPA criteria recommendations for pathogens
0.1% had microcystins concentrations exceeding the EPA recommended recreational swimming advisory level
24% (25,119 river miles) of the sampled population of river miles had mercury concentrations in fillet composite samples that were above the EPA fish tissue-based water quality criterion recommendation for methylmercury
40% (24,583 river miles) had PCB concentrations above the EPA human health f ish tissue benchmark.
3% (3,490 river miles) had had concentrations of perfluorooctane sulfonate (PFOS), one of the most dominant PFAS in freshwater fish tissue, that were above the EPA human health fish tissue benchmark in fish fillets
Ray of Light: How can we naturally decrease the effects of pollution?
The need for solutions to water pollution is urgent. Pollution from sewage effluent and industrial waste negatively affect the clean water supply distributed to populations, especially communities of color.
Phytoremediation is introduced as an alternative to replace traditional treatment methods. Phytoremediation consists of a group of technologies that use naturally occurring or genetically engineered plants to reduce, remove, break, or immobilize contaminants. These methods are known for their sustainability—with minimal maintenance and energy costs (Marcos et al., 2014).
Photo by Virginia Tech Extension
Floating Treatment Wetlands (FTW/For the Win?)
A phytoremediation effort called the Floating Treatment Wetlands (FTWs) aims to replicate the functions of a traditional wetland, where water quality is maintained or improved in several ways:
Nutrient removal and retention
Processing of chemicals and organic materials
Reduction of sediment load of water
Floating treatment wetlands are small artificial platforms vegetated with aquatic emergent plants with both high pollutant uptake capacity and high growth rate (Marcos et al., 2014). The roots of these plants extend down into the contaminated water, acting as a biological filter. FTWs absorb nutrients and potentially toxic metal(s) and element(s) from polluted water through their roots. The microbes present on FTWs break down organic matter and create biofilms, which consume nitrogen and phosphorous, and convert these contaminants into less harmful substances (Shahid et al., 2018).
Functions of Floating Treatment Wetlands
Maintain or Increase Biodiversity
When a planted island is placed in a waterbody, biofilm starts to grow around and through the plants and roots which acts as a natural cleaning system. Nutrients are recycled into periphyton, which turns into food for fish. As a result, there are fewer algae blooms, more natural wild fish, and increased biodiversity (International Institute for Sustainable Development, 2019).
Other functions include:
Sustains a biodiverse population
Improves water clarity and shade out underwater weeds
Facilitates cost-effective mosquito and midge control
Learn more about the research behind the increase of total fish biomass through FTWS. Click here.
Shoreline and Coastal Restoration
FTWs act as wave mitigators: they disperse the kinetic energy of incoming waves to efficiently lower wave height and energy (Webb, 2014).
Other functions include:
Mimics natural sedimentation processes in coastal habitats
Protects shorelines from erosion caused by wave action and boating activity
Floating structure solves sinking issues by rising and falling with the tide
Interested in learning more about the research behind wave transmission and FTWs? Click here.
Stormwater Management
FTWs are a "retrofit" for stormwater management because they do not require earthmoving, eliminate the need for additional land to be dedicated to treatment, and will not detract from the required storage volume required for wet ponds (Winston et al., 2013). They also adjust to fluctuating water levels in stormwater ponds, which allows capability to overcome technical and operational challenges and treat highly variable flows (Sharma et. al., 2021)
Other functions include:
Manages nutrient runoff and prevent algal blooms
Capture sediment before it enters pond and lakes
Wastewater Treatment
Removing pollutants from effluents is one of the main functions of FTWs. Plant roots grow unhindered through the porous matrix, creating a large surface area within and beneath the wetland for bacteria to digest organic debris and nutrients in wastewater (Afzal et. al., 2019). Suspended particles are either digested or sloughed off. Plant-microbe symbiosis boosts both microbial activity and plant development, resulting in an unrivaled, natural, and low-cost water-cleaning solution.
Other functions include:
Odor mitigation
Phosphorous removal
pH stabilization
Considerations for policy-making processes
FTWs can be quickly established as "natural infrastructure" in any water body as a managed phytoremediation system. Implementation of FTWs should be considered in environmental and conservation management efforts. To ensure the relevance and value of future allotment of funding, we should look at FTW cost-effectiveness and environmental impacts.
Cost-Effectiveness:
In terms of economic variability, there was a substantial impact on the overall cost of nutrient removal, with savings of up to 86% and 42% for biochemical oxygen demand and phosphorus removal, respectively, especially at low concentrations and flow rates (Firth et al., 2020).
Optimal performance in the second and third years of operation during which about 60 million m3 per year of wastewater was treated at a cost of US$0.00026 per m3 (Afzal et al., 2019).
No land costs parameters for FTWs; they stay afloat in the water.
Environmental Impact:
Promotes substantial improvement of water quality indicators and a reduction of heavy metal concentrations in the effluent (Afzal et al., 2019).
Considered a nature-based solution with great potential to increase biodiversity by providing additional wildlife refuge (Calheiros et. al., 2020)
Future Directions
FTWs offer a promising solution in the remediation of toxic heavy metals, nutrients, suspended solids, and other pollutants from wastewater. However, plant adaptations, above-ground and below-ground biomass development, metal tolerance limits, and symbiotic interactions between flora and micro-fauna should be investigated further (Sharma et al., 2021).
One limiting factor of FTWs is the weakened or reduced performance of the metabolic plant and microbial activity during low-temperature conditions (Kumwimba et al., 2021). Future research is needed to enhance FTW efficacy and management under cold conditions to ensure sustainability in the long run.
How can we increase funding for the implementation of FTWs in areas of low-income and minority communities? What significance would this have on eliminating environmental racism for these populations?
References
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