Scientists at the Metropolitan Water Reclamation District of Greater Chicago (MWRD) are assessing the potential of using plants to filter unwanted pollutants from wastewater and surface water streams.

The MWRD researchers at the O’Brien Water Reclamation Plant in Skokie, Ill. are studying the feasibility of phytoremediation, a process where plants are used as a tool to clean contaminated environments. Wetland plants can help prevent wind, rain, and groundwater flow from carrying contaminants away from one site to another or deeper underground, but the plants can also clean up a variety of contaminants like metals, pesticides, explosives and oil in water itself.

These valuable plants can also address nutrient pollution. Agricultural runoff, urban development and industrial activities have elevated the flow of nutrients in waterways throughout the world. These nutrients, such as phosphorus and nitrogen, deprive water of oxygen, deteriorate water quality and contribute to harmful algal blooms and hypoxic “dead zones” that pose grave ecological and economic challenges. These pollutants have surged in recent years, intensifying the environmental burden on aquatic ecosystems.

Phytoremediation with aquatic plants or Artificial Floating Islands (AFIs) is one strategy that could be used to reduce nutrient pollution. However, more testing is needed before it is widely used. Aquatic plants can be cultivated directly in wastewater, and AFIs are hydroponic systems where wetland plants are suspended by a floating raft in wastewater. In both cases, the plants and bacterial communities attached to their roots consume phosphorus and nitrogen, resulting in cleaner water, and plant growth that can be harvested and utilized, transplanted, or kept in place.

“Phytoremediation represents a real opportunity to better manage nutrients and other forms of pollutants in water,” said MWRD President Kari K. Steele. “I applaud our Monitoring and Research Department for taking the lead on these studies that can make a broader impact on our water environment and the way we address nutrient runoff and contaminants in wastewater treatment.”

Duckweed, the smallest flowering plant known to exist, and several wetland species in AFIs can remove nitrogen and phosphorus from treated wastewater and could possibly further reduce the nutrient load to receiving waters. The next step will be to further explore at pilot scale and then scale up the technology, testing how the process could work outdoors exposed to extreme realities of the Chicago climate. Once the field test phase is completed, a comprehensive analysis will be conducted to evaluate both its environmental impact and the practical operational considerations. This holistic assessment will provide valuable insights into the technology’s real-world potential and pave the way for its broader implementation.

“We already use microorganisms for the majority of our nutrient sequestration,” said MWRD Commissioner Eira Corral Sepúlveda “It makes sense to investigate other organisms that could help with the wastewater treatment process, and at the same time, try to reduce our carbon footprint. Here we can provide multiple benefits.”