How the treatment works
Treatment is achieved through the combined action of the gravel substrate, the plants, the wastewater and the microorganisms present within it. Inside the gravel bed, as wastewater passes through, microorganisms develop and trigger biochemical reactions that degrade the pollutants.
The plants not only actively participate in the elimination of contaminants, but also supply the oxygen required for these reactions by transporting it from their foliage down to the rhizosphere. For this reason, only plant species with specific characteristics can be used in constructed wetlands. The most widely used species internationally are Phragmites Australis, Carex, Juncus, Typha and Iris.
The system works without any added energy input and therefore without any electromechanical parts, making it fully eco-compatible. Correctly designed and built constructed wetlands achieve an organic load reduction of over 90% and always comply with legal limits.
Design parameters
For residential systems, the design is based on a daily per-capita discharge of 200 litres, a per-capita BOD5 load of 60 g/day and inlet pH between 6 and 8.
Constructed wetland systems are designed to:
- Simplify operation and maintenance while minimising investment and running costs, using the lowest possible technology intensity and energy consumption
- Withstand hourly and seasonal variations in hydraulic and organic loads
- Provide effective treatment even for small and dispersed facilities, avoiding the need to collect low flows over long distances
- Allow for reuse of treated water for irrigation
- Minimise visual impact and disturbance to neighbours
- Protect groundwater, especially in zones vulnerable to nitrate pollution
Construction
A constructed wetland is built by excavating a basin of variable dimensions, lined with a waterproof PVC membrane to ensure complete containment. The waterproofed basin is then filled with selected aggregate and planted with emergent macrophyte species.
The effluent level inside the basin is maintained approximately 10–15 cm below the gravel surface by means of the patented Guida Battente® level-control device. The surface is therefore walkable, free from odours and not a breeding ground for insects.
Flow types
Horizontal Subsurface Flow
Max depth 0.8 m. Most common type — easy to build and manage. The wastewater flows horizontally through the gravel bed.
Vertical Subsurface Flow
Max depth 1.1 m. Allows a smaller footprint but requires an equalisation tank, increasing complexity.
Combined Flow
Horizontal and vertical stages in series. Optimal treatment performance for complex or high-load discharges.
Suitable plant species
Only Phragmites Australis, various varieties of Typha, Juncus, Carex, Scirpus and, secondarily, the yellow marsh iris may be used in constructed wetlands. All plants are included in the FitoBox® kit price and grown from certified seed stock.