Learn more about constructed wetlands


Water has always represented an asset of primary importance for the life of all living beings. The growth of the population and the productive activities related to it have led to a strong conflict for the use of water resources, also accentuated by its progressive degradation in quality because of the pollution processes. The alteration of the environmental quality of water bodies involves the alteration of biodiversity, less availability of the water resource for human consumption, and, sometimes, also a threat to the health of living species, including humans. At the national and European level, water policy aims to ensure the satisfaction of human and environmental water needs through the maintenance of high-quality standards. It should be considered that, according to the national summary data for surface waters, only 43% of the rivers achieve the quality goal for the ecological status and 75% for the chemical status.

Among the origins of water pollution, it is important to distinguish the nonpoint and point sources. In this regard, all activities related to the agricultural, forestry and livestock sectors may release pollutants into the environment in a variable way in space and time (nonpoint sources of pollution); instead, all productive activities, including industrial and civil settlements, contribute to pollution in a precise way in space and time (point source of pollution).

Bioremediation is a general term identifying a set of natural processes of wastewater treatments due to the triple interaction water-biosphere-soil system. In this context, constructed wetlands are a natural water purification technique that is based on the principle of reproducing the same chemical, physical and biological self-purification processes that characterize aquatic habitats, swamps and natural wetlands. In most cases, constructed wetlands represent a secondary or tertiary treatment, downstream of the traditional purification processes, even if in some cases excellent purification performances are obtained after a pre-treatment suitable to eliminate only coarse materials.

Constructed wetlands are usually classified based on the following criteria: i) hydrology (surface or sub-surface flow), ii) flow path (horizontal or vertical), iii) type of plant species (emergent, submerged or free-floating). By combining the above information, constructed wetlands systems are divided into:

  1. surface flow constructed wetlands, that is dug basins, characterized by 20-30 cm of soil or substrate and 30-40 cm of water, in which wastewater flows slowly, passing through non-vegetated areas suitable for the sedimentation of the particulates and vegetated bands with macrophytes arranged perpendicular to the direction of the flow;
  2. floating surface flow constructed wetlands, made by exploiting floating hydrophyte species such as aquatic lettuce hyacinth or, much more often, traditional perennial herbaceous macrophytes supported by a floating support;
  3. sub-surface flow constructed wetlands, conceptually different from those with surface flow, in which the wastewater is never brought to the surface. In horizontal flow systems wastewater flows parallel to the structure, in vertical flow systems wastewater percolates, moving from the surface of the substrate into depth;
  4. hybrid constructed wetlands, born as a combination of two or more depuration systems (sub-systems), connected in series.

Constructed wetlands were developed as an eco-technology for the treatment of different types of waste, including agricultural drainage and zootechnical wastewater, urban run-off water, by-products deriving from industrial activities (food industries, wine production, slaughterhouses, paper mills, textile sectors, car washing), but the prevalent use concerned municipal wastewater. The most adapted plant solutions concerned the use of hybrid systems, capable of exploiting the specific purification performance of each sub-system. These systems proved to be quite promising, reducing the concentrations of total nitrogen up to 95%, nitric nitrogen up to 89%, ammonia nitrogen up to 99%, total phosphorus up to 94% and organic matter up to 95%.

As previously anticipated, constructed wetlands are distinguished from common lakes or reservoirs of accumulation of rainwater due to the presence of vegetation. The latter fulfils several equally important roles:

  1. physical: conversion of solar energy by photosynthesis, reduction of the volume of the wastewater by evapotranspiration, stabilization of the filling substrate by roots and rhizomes, filtration of the wastewater, air conditioning effect, transport of atmospheric oxygen to the wastewater through the aerenchymatic tissues;
  2. biological: absorption and removal of nutrients, heavy metals and pollutants in general, emission of enzymes, roots exudates and allelopathic substances, support for the microbial population;
  3. secondary: aesthetic-ornamental value, production of biomass for bioenergetic purposes, refuge for animal biodiversity (amphibians, fry, macro-invertebrates and sometimes even birds).


Recently a new technique has been developed, called floating constructed wetlands, with the aim of treating different types of wastewater in basins, canals or water bodies in general. The system involves the use of floating platforms, capable of supporting traditional macrophytes not naturally floating. Different matrices have been used for the realization of the floating modules, adopting both organic materials (coconut fibre, bamboo) and inorganic materials (plastic, PVC, rubber). At this matter, in Italy the Tech-IA system was developed by PAN/De Rebus Plantarum. It consists of a floating platform built in a non-toxic material, characterized by high resistance to chemical, physical and biological agents when placed in water. The system is well qualified to support any plant, both herbaceous and shrubby, thus expanding the range of species that can be used in the field of floating constructed wetlands. The use of the Tech-IA system has so far been exploited for the purification of different types of wastewater, such as: agricultural drainage water, municipal wastewater, river water, wastewater from fish farms as well as from anaerobic digestion systems, showing a particular efficacy in reducing water turbidity, in removing nutrients, nitrogen and phosphorus, as well as organic matter.

Although the Tech-IA system was created to fulfil the purification of all water bodies, where due to lack of space it is not possible to design other constructed wetlands systems, it can also be used in the creation of vegetated islands for naturalistic/faunal purposes, of floating barriers with or without vegetation, with the function of delimitation and signalling, of decorative islands in natural, artificial, public and private bodies of water, of supports for horticultural species and flowers grown in hydroponics.

An example: simulation of the visual impact obtained with the application of the Tech-IA system in the Botanical Garden of Padova.

simulation of the visual impact obtained with the application of the Tech-IA system in the Botanical Garden of Padova


Examples of usable plant species:

Iris pseudacorus

Canna indica

Lythrum salicaria

Calla palustris

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