Sistemas de fitodepuración

The function of aquatic plants is to create a suitable habitat for the growth of bacterial flora.

In practice, aquatic plants capture oxygen from the atmosphere and carry it from the leaves, via the stem, to the roots (or rhizomes) of the plant and then into the rhizosphere (the layer of soil in which the plant’s rhizomes are located), making it available to the aerobic bacteria in the substrate.

These bacteria that live in symbiosis with the plants, in fact, need oxygen to live and perform their function.

Their role is to degrade pollutants and organic substances by transforming them into inorganic substances available to plants.

Plants in turn also contribute to purification because they absorb as nutrients for their growth some of the substances dissolved in water and transformed by the bacteria.

In addition, the plants have the function of shading the surface of the body of water and thus regulating the temperature of the effluents (too high temperature can reduce the vital functions of the bacteria).

The areas of the phyto-purification system that cannot receive oxygen are home to anaerobic bacteria, which also contribute to the purification process.

A phyto-purification system is able to fulfil its function already a few months after the start of its operations, particularly if the planting of aquatic plants is done in the spring.

The species of aquatic plants to be used are different depending on the type of phyto-purification system that has to be builded.

To learn more about the concepts of phyto-purification and the balanced aquatic habitat download the free “Guide to Growing Aquatic Plants“.

Types of phyto-purification systems

Phyto-purification systems are classified according to the characteristics of the tank and the path the effluents take within the reservoir:

• Phyto-purification by Free Water Surface Systems,
• Floating phyto-purification,
• Phyto-purification by Horizontal Subsurface Flow Systems,
• Phyto-purification by Vertical Subsurface Flow Systems,
• Hybrid Systems.

Phyto-purification by Free Water Surface Systems

This type of system is the simplest, in fact it consists of a shallow waterproof tank like a classic pond. A substrate is placed at the bottom of the tank in which aquatic plants are planted.

The plants used can be:

• marsh plants (such as Pontederia cordata, Sparganium erectum, Iris pseudacorus, Schoenoplectus lacustris, Glyceria maxima Variegata, Butomus umbellatus),
• water lillies and nuphar,
• submerged oxygenating plants (such as Ceratophyllum demersum, Myriophyllum spicatum, Elodea canadensis).

This type of system, when compared to Subsurface Flow Systems, requires more surface area in order to get the same purification power.

This system is only used to treat lightly polluted water (e.g. as a secondary tank in a koi carp lake, or as part of a natural pool) or as a final treatment downstream of a Subsurface Flow Phyto-purification Systems.

If this system were used for the phyto-purification of highly polluted water, there would be the problem of bad odours and a lot of algae would form on the surface. So for example for water from sewers or farms, only the Subsurface Flow Systems is used.

In this picture you can see a diagram of a Free Water Surface Phyto-purification Systems. (Source: ISPRA, 2012)

Floating phyto-purification

Among the phyto-purification by Free Water Surface Systems, the floating phyto-purification system is becoming increasingly popular. This involves the use of floating supports (a sort of raft) on which marsh plants (particularly effective in phyto-purification) are placed, which otherwise could not float.

This system is particularly useful for purifying canal or river water, where it is not possible to root plants at the bottom.

In order to build a floating phyto-purification system, a floating barrier must be created transversal to the stream, installed from one bank to the other, using a raft created in DIY mode or with the patented Tech-IA modules.

A Tech-IA element is rectangular in shape and weighs approximately 2 kg. It has high mechanical strength, high resistance to chemical, biological and climatic agents and can support a load of up to 20 kg. Each element is equipped with eight grids to accommodate the plants for phyto-purification and six holes for anchoring to the other elements and to the banks for static anchoring.

The floating barrier is anchored to the shore by means of ropes and pickets, or to the bottom of the body of water by means of dead weights, leaving plenty of rope to facilitate fluctuations on the water level during very rainy periods.

Marsh plants to be used in the floating phyto-purification system can be for example Iris pseudacorus, Glyceria maxima Variegata, Carex pseudocyperus, Carex riparia, Juncus effusus.

The roots of the plants can descend up to one metre into the water beneath the floating modules, thus creating a biological filter for pollution control.

In addition, this system also provides an interesting habitat for fish and aquatic birds that can find shelter among the plants.

Phyto-purification by Horizontal Subsurface Flow Systems

Phyto-purification by Horizontal Subsurface Flow Systems consists of an impermeable tank filled at the bottom with a layer of gravel into which the effluent flows horizontally.

In this way, the liquids do not come into contact with the air and the problem of odours is avoided.

Plants are planted on top of the gravel layer through which the effluent flows and thus the roots will grow inside the gravel, creating aerobic purification zones, interspersed with anaerobic purification zones.

In this type of system, marsh plants are used such as Phragmites australis, Iris pseudacorus, Glyceria maxima Variegata, Carex pseudocyperus, Carex riparia, Juncus effusus, Cyperus longus.

This type of plant is used for the treatment of civil and industrial waste water and for the treatment of agricultural effluents.

I report here the results of analyses carried out on an experimental Horizontal Subsurface Flow Phyto-purification Systems in Lugo di Baiso (RE) in operation since 1996. The plants used are Phramites Australis.

• Organic waste substances removal efficiency (BOD): 90% (60/70% in winter),
• Total suspended solids removal efficiency: 90%,
• Bacteria removal efficiency: 90/99%,
• Nitrogen and phosphorous removal efficiency: up to 90%.

In this picture you can see a diagram of a Horizontal Subsurface Flow Phyto-purification System. (Source: ISPRA, 2012)

Phyto-purification by Vertical Subsurface Flow Systems

The Vertical Subsurface Flow Systems consists again of an impermeable tank in which plants are placed on top of a layer of gravel, but the effluents is intermittently percolated from above by a pump.

This system has the advantage of facilitating the diffusion of oxygen within the substrate.

With each filling, in fact, the substrate also traps the air in depth, forming colonies of aerobic bacteria even in the deepest and least colonised part of the roots.

In this type of system, marsh plants are used such as Phragmites australis, Iris pseudacorus, Glyceria maxima Variegata, Carex pseudocyperus, Carex riparia, Juncus effusus, Cyperus longus.

This type of system is also used for the treatment of civil and industrial waste water and for the treatment of agricultural effluents.

In a Vertical Subsurface Flow Phyto-purification System of mixed water in the municipality of Gorizia, in operation since 1995, these values were recorded:

• Organic waste removal efficiency: BOD 90% and COD 65%,
• Ammonium removal efficiency: 60%,
• Total nitrogen removal efficiency: 75%,
• Phosphate removal efficiency: 90%,
• Total and faecal coliform removal efficiency: > 99%.

In this picture you can see a diagram of a Vertical Subsurface Flow Phyto-purification Systems. (Source: ISPRA, 2012)

Phyto-purification by Hybrid Systems

Different types of phyto-purification systems can be combined with the aim of optimising the purification yields of particular types of waste water in industrial or agricultural contexts.

For example, it is possible to build several subsurface phyto-purification tanks in cascade and then downstream a free water surface tank (such as a pond).

Fields of application of the phyto-purification

With phyto-purification systems it is possible to purify:

• ornamental ponds with fish (such as koi carp), turtles or ducks,
• natural pools or swimming ponds,
• agricultural and agri-food effluents,
• agricultural effluents from wine production,
• agricultural effluents contaminated with pesticides,
• effluents from stables, kennels or livestock farms,
• effluents from civilian dwellings, from single villas to entire mansions,
• effluents from agritourisms and campsites,
• industrial effluents,
• effluents from wineries and dairies,
• leachates from mines and landfills,
• derivations from eutrophicated streams.

In the absence of public sewage, household sewage can then be purified through a phyto-purification system. Of course, sewage must be separated upstream through an IMHOFF pit or septic tank.

Advantages of phyto-purification

Benefits of using phyto-purification include:

• Reduced system costs,
• Absence of energy consumption,
• Reduced operation and maintenance, executable even by non-specialized personnel,
• Saving of kilometers of pipe for connection to sewers,
• Possibility to reuse outgoing water where potable water is not needed (toilet cistern, irrigation, etc…),
• Savings in electricity compared to normal purification systems,
• Long service life.

Use of phyto-purification systems today

Tens of thousands of phyto-purification systems are currently in operation in Europe, most of them located in northern countries where they have been used for many years for reducing pollution from small and medium-sized users.

In Europe and Italy, horizontal and vertical subsurface flow systems are the most widely used (more than 75%), mainly for secondary treatment of domestic and civil waste water.

Subsurface flow systems are the most widely used in our areas for these reasons:

• easy environmental integration in urban and/or peri-urban areas,
• high purification efficiency even in the winter months,
• greater ease of operation and maintenance,
• absence of problems related to the occurrence of bad odors and the presence of insects,
• better ratio between required surface area and treatment efficiency.

The use of phyto-purification systems for waste water treatments in recent years are increasing significantly, and we are even more hopeful for the future!

If you want to set up a phyto-purification system, we can provide you with the waterproofing liners and plants best suited to your specific case.

Contact us through the channels indicated on the Contact page!