Phytodepuration: what it is and how it works

Phytodepuration is a natural wastewater treatment system for domestic and agro-industrial wastewater that utilizes the self-purification principle typical of aquatic environments. The purification occurs through specific interactions between soil, bacteria, and plants.

The phytodepuration system, to optimize its purification processes, requires primary treatments installed upstream of the plant for the pretreatment of both black and gray wastewater, such as septic tanks, two-chamber biological tanks, three-chamber biological tanks, Imhoff tanks, and grease traps.

The consolidated environmental text, Legislative Decree 152 of 2006, part three, encourages natural purification plants that meet the requirements of "appropriate treatment"
Appropriate treatments are indicated by Legislative Decree 152/06 as well as by the regions that are mandated to legislate by Articles 100 and 101 of Legislative Decree 152 and must have the following characteristics:

• low installation simplicity
• ease of management and maintenance
• effectively support variations in hydraulic load, organic load, and overall pollution of wastewater, ensuring purification efficiency in both the short and long term
• be economically compatible with the benefits they bring to the discharge of treated wastewater, whether it is surface water or soil

If properly sized, designed, and maintained, phytodepuration plants may not require the replacement of aquatic plants, except for causes not dependent on the integrated wastewater treatment system.

Regarding their sizing, the required surface area varies depending on the characteristics to which the outgoing effluent must be directed (discharge into a watercourse, discharge onto soil, reuse for irrigation purposes, or replenishment of toilet cisterns, etc.), as well as the installation area, such as arid zones, coastal areas, mountainous areas, etc.
Generally, for a domestic-type discharge, the surface area for phytodepuration can vary from 2 to 10 square meters per equivalent inhabitant.

Phytodepuration systems are comparable to adhered biomass systems of the aerobic type (percolating filters). The plants planted on the phytodepuration bed have a natural ability to transport oxygen and conduct it, through the stem, to the roots (rhizomes) located deep (typically no more than 1 meter). The surface of these, just a few months after the start-up of the plant, will be covered by a bacterial film of microorganisms, the real agents responsible for the wastewater purification process. The appropriate choice of the filling material for the phytodepuration bed, made by professionals, will allow for natural and constant oxygenation, so that the microorganisms can always be efficient and suitable for wastewater treatment.

The construction of phytodepuration plants consists of excavation and the installation of tanks that can be pre-assembled in concrete, high-density polyethylene, fiberglass, and/or various thicknesses of waterproof HDPE sheets, filled with permeable substrate (generally gravel/sand of different grain sizes). On the surfaces thus obtained, pipes for the distribution of the effluent are positioned either with a vertical load system or with a horizontal load system, and the aquatic plants are planted.

The two types of plants, horizontal and vertical, can also be used in combination for better purification results, particularly for nitrogen reduction.