Plants as cleanup agents
Phytoremediation uses plants to stabilize, extract, or transform contaminants in soil and water. Wetlands naturally process nutrients and some pollutants — designed systems scale this capacity.
Mechanisms
- Rhizofiltration — roots absorb dissolved metals and nutrients.
- Stabilization — roots bind soil, reducing erosion of contaminated sediment.
- Degradation — rhizosphere microbes break down organic pollutants.
Design considerations
Retention time, hydraulic loading rate, and plant species tolerance to contaminant levels. Harvesting biomass may be required for metals to remove them from site — otherwise metals remain in tissue on site.
Limitations
Not a substitute for source control of pollution. Long time scales and monitoring for breakthrough during extreme flow events.