Constructed wetlands are a natural process used to treat polluted water based on the capability of soil and vegetation to remove pollutants. They are designed as a system of biological ponds and of planted macrophyte vegetation. The purification process is completely environmentally friendly and does not involve the use of chemicals. The wastewater arriving at the constructed wetlands plant flows into a bed of gravel and aquatic plants: here many different species of microorganisms come into play and through biochemical reactions, eliminate the pollutants present. The action of the plants is fundamental because the micro-organisms necessary for the entire system develop in their roots; they absorb the oxygen produced by the plant species and trigger the processes necessary for purification of the wastewater.
This kind of treatment also contributes to the reclamation of borderline areas, creating natural environments and landscapes that are pleasing to the eye, and often chosen as refuges for various species of birds, amphibians and reptiles.
Hera operates 17 small or medium-capacity constructed wetlands, located in the provinces of Bologna, Florence, Forlì-Cesena, Rimini and Ravenna: some are secondary biological treatment plants downstream of primary sedimentation while others are tertiary treatments used for final refinement of the wastewater before its final discharge. Marche Multiservizi operates 5 constructed wetlands plants with a potential of between 80 and 180 population equivalents.