Rhizofiltration is a water treatment technology that uses plant root systems to remove contaminants from aqueous solutions through adsorption, absorption, and precipitation processes within the rhizosphere. This approach primarily employs constructed wetland systems where aquatic and terrestrial plants are strategically positioned to filter pollutants from contaminated surface water, groundwater, and various industrial effluents. The process relies on the extensive root networks of selected plant species to capture heavy metals, excess nutrients, and organic contaminants, often concentrating them in root biomass or precipitating them as metal-plaque formations on root surfaces through oxygen release via root aerenchyma.
This treatment method is particularly effective for managing large volumes of water with relatively low contaminant concentrations, making it ideal for municipal wastewater treatment, stormwater management, and industrial effluent polishing rather than primary treatment. Rhizofiltration excels in scenarios requiring continuous, long-term water treatment where aesthetic considerations and ecological co-benefits are valued. It is especially suitable for treating acid mine drainage, agricultural runoff, and cooling water systems where conventional treatment methods may be cost-prohibitive or environmentally disruptive. However, it is not appropriate for emergency spill response, highly concentrated contamination requiring rapid treatment, or situations where complete contaminant removal is mandated within short timeframes.
The advantages of rhizofiltration include its low energy requirements, minimal chemical inputs, and ability to integrate water treatment with habitat creation and carbon sequestration. The technology can effectively remove heavy metals such as cadmium, lead, copper, chromium, and zinc, while simultaneously addressing nutrient loading from nitrogen and phosphorus. Constructed wetland systems can be designed as free water surface or subsurface flow configurations, allowing flexibility in meeting site-specific hydraulic and treatment requirements. Additionally, the approach provides opportunities for biomass harvesting and potential metal recovery from plant tissues, supporting circular economy principles.
Implementation challenges include the need for specialised plant selection based on target contaminants, seasonal variations in treatment efficiency, and requirements for long-term biomass management. The technology is limited by rooting depth constraints and may require multiple growth/harvest cycles to achieve regulatory compliance. Contaminated plant biomass requires careful handling and disposal, often necessitating incineration or specialised waste management protocols. Integration with other treatment technologies is frequently necessary to achieve comprehensive remediation objectives, as rhizofiltration alone rarely constitutes a complete treatment solution. Success depends on appropriate hydraulic design, regular monitoring, and ongoing vegetation management to maintain system performance and prevent ecological disruption.