Phytodepuration: the most natural way to purify wastewater

Phytodepuration is a natural wastewater purification system that uses the principle of self-purification typical of aquatic environments. Purification is carried out through specific interactions between soil, bacteria and plants.

Upstream of the process, a primary treatment must be carried out to remove coarse solids through a sedimentation phase and a mechanical treatment of solid-liquid separation that eliminates almost all the solid matter.

After this phase, our wastewater is ready to begin the phyto-purification process using physical, chemical and biological pollutant removal mechanisms (organic matter, nitrogen, phosphorus and pathogens) that mimic those that occur naturally in aquatic areas and wetlands (e.g. swamps).

How does it work?

A= Diagram of the matter cycle for carbon in a closed ecosystem
B= The same simplified diagram
P= Photosynthesis
R= Respiration
(From ANPA manual).

In the diagram we can see what processes are involved in water purification in a naturally occurring closed ecosystem, such as a pond. In this type of environment there are purification systems based on the interaction between the different forms of life that inhabit that space.

More simply, organic carbon is transformed into inorganic carbon by the respiration processes of living things, then made organic again by plants through photosynthesis.

The self-purifying capabilities of these environments can cope with a limited load of pollutants. To treat larger volumes it is necessary to build a real phytodepurator to amplify the natural process to the maximum.

Biological purification processes

To understand how the purification of pollutants in domestic, agricultural or industrial wastewater takes place, we must first understand the biological processes that regulate the functioning of this system:

Photosynthesis: a process carried out by all plants present in the system, from algae to plants. Using carbon dioxide present in the atmosphere and sunlight, it allows the synthesis of oxygen and carbon (along with hydrogen from water) into glucose, a sugar of fundamental importance to plant life. These same chemical elements are also used in the processes of nitrification and respiration, moreover the roots transport part of the oxygen to the rhizosphere (the portion of soil that surrounds them) creating aerobic pockets in which microorganisms useful for the process of water purification can proliferate.

Respiration: in the aerobic phase (therefore in the presence of oxygen) the glucose produced through photosynthesis is transformed into energy by the heterotrophic organisms present in the phytodepurator. The resulting waste products are carbon dioxide and water.

Fermentation: in anaerobic phases (i.e. in the absence of oxygen) the organic substance decomposes thanks to some species of microorganisms which, with their metabolic action, transform it into methane, ammonia, hydrogen sulphide and volatile fatty acids.

Nitrification and denitrification: transformation of ammonia present in the soil into elemental nitrogen N2 and nitrates NO3-. In this way in the beds in aerobiosis (vertical flow – nitrification) and in anaerobiosis (horizontal flow – denitrification) the oxidized ammoniacal nitrogen is removed by assimilation (it becomes plant food) or by gasification (it becomes a gas that is released into the atmosphere).

Phosphorus removal: a process carried out by biofilms and macrophytes (macroscopically visible plants present in aquatic, marsh and gravel environments) which, by storing the phosphorus present in the wastewater, make it easy to remove from the sewage sludge.

The article continues…


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Alberto Franco
Alberto Franco

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