Phytoremediation: Floating Treatment Wetlands

• • • 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.

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.

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).

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

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?

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