About constructed wetland
With a constructed wetland plant it is possible to treat any type of civil and industrial wastewater. The technique consists in digging a water reservoir, waterproofing it and filling it with soil in which the purifying plants will be planted. This “basin” will be irrigated with the wastewater to be purified: the irrigation water will be subject to the joint purifying action of roots and bacteria and will be convoluted downstream of the system. Alternatively, it is possible to opt for the creation of surface flow ponds, which are nothing more than ponds whose flora, planted on the banks and in sections transversal to the water flow, will be selected in order to obtain the required purification results.
The purified water obtained in this way will have the suitable characteristics to be discharged on the ground, in a body of water receptor, or reused for irrigation or flushing system of the toilets of our house.
In addition to this, the installation of a constructed wetland system involves the creation of a new wetland in our territory and therefore a habitat for animal and plant species that were not present before, stimulating the biodiversity of the territory.
All this takes place with practically no energy requirements, especially if the plant is built by gravity without the need for pumping. Unlike a conventional plant, a constructed wetland plant reduces CO2 emissions, the consumption of raw materials (cement, iron, etc.) and chemical products to zero.
Types of plant
A constructed wetland plant is generally placed after a primary treatment, such as grilling, de-oiling, sedimentation or Imhoff tank. This primary phase has the task of making the water to be treated suitable for constructed wetland and allows a stable and efficient process.
With the constructed wetland a controlled natural system is created, able to remove pollutants and organic substances present in the water.
In order to manage this natural process it is necessary to create waterproofed beds filled with material suitable for plant growth. The waterproofing prevents the dispersion of pollutants and water in the soil below.
The plants used stimulate natural processes that allow, around the roots, to create the ideal conditions for the establishment of bacterial colonies that use pollutants as nutrients.
The filling material also has a purifying action in itself, thanks to the filtering properties of the medium itself (mixtures with gravel or fine cobblestones).
The system solutions are divided into three categories:
– horizontal submerged flow systems: tanks sealed and filled with gravel, in which the wastewater is fed under the surface of the bed. They have a good performance in terms of removal of organic pollutants (BOD), metals, suspended solids, phosphorus and surfactants;
– vertical submerged flow systems: the tanks appear similar to those for horizontal submerged flow, only that the wastewater is fed through sprinklers, which have the function of oxygenating the water to be treated, increasing nitrogen removal;
– free-flow systems: they appear as small ponds or ponds, where the plants are made to develop along the banks and in cross-sections to the flow. The depth is about 50 cm and among the main advantages are the pleasant environmental integration and the promotion of biodiversity due to the creation of a wetland. The removal efficiencies are comparable to the other two systems, but should almost always be placed downstream of one of the two, so as to avoid the spread of bad smell due to the introduction of too much polluted wastewater.