As in all wastewater treatment plants, the biological treatment performance in a constructed wetland is carried out by microorganisms. In technical systems like (settle on a fixed bed, a trickling filter or a disc immersion tank); in other systems, they float on sludge flocs in the wastewater. In reed bed treatment systems, the microorganisms live on the surface of the substrate and feed on the dirt load carried by the wastewater. The porous soil in combination with the root system of the plants creates an ideal environment for the process of wastewater treatment. In addition to biological (microbial degradation), a mechanical (filtering effect) and physicochemical processes (adsorption and precipitation) also play an important role in wastewater treatment.
In tests on our soil filters, we were able to determine that organic pollution is already reduced by up to 90 % in the uppermost soil layers by microbial activities. A prerequisite for good carbon decomposition is the regular supply of oxygen to the microorganisms. This is achieved by intermittent feeding, i.e. feeding with alternating longer dry and wet phases.

In domestic wastewater, nitrogen occurs in the form of ammonium nitrogen (NH4 -N). Ammonium nitrogen can be converted into toxic ammonia in the water and then becomes a danger to aquatic fauna. Keyword: fish mortality.

In our vertical flow constructed wetlands, the ammonium nitrogen is removed from the wastewater by oxygen-loving (aerobic) microorganisms and converted to nitrate in the upper soil zones. This nitrate-nitrogen (NO3 -N) remains in the treated wastewater as the end product of nitrification. For the removal of nitrate-nitrogen, a further clarification stage is necessary, in which denitrification takes place.

If denitrification of the nitrate is required, we add a lushly planted pond, for example, to our vertical flow filters. [DETAILS ERGÄNZEN] The wastewater is continuously discharged into the deeper water layers, where atmospheric nitrogen (N2) is reduced from nitrate nitrogen (NO3 -N) under anaerobic conditions. This nitrogen then escapes into the atmosphere or is bound in the plants.

In a constructed wetland, phosphate is partially removed from the wastewater stream via biological processes and stored in the plants. These are microorganisms that live in a changing environment of oxygen-rich and -poor zones, where they provide phosphorus reduction in a biological manner. Phosphorus can also be fixed in the soil filter or in a downstream unit, through the incorporation of substrates high in iron and aluminum salts, to which phosphates bind by adsorption.

The human body is colonized by millions of bacteria without which, for example, the entire metabolism would collapse. Pathogenic bacteria or germs are often found in wastewater, as they are naturally excreted by the human body. If such pathogens get back into a human body, there is a risk of infections and diseases.

In Germany, germ elimination in wastewater treatment plants is state of the art. Here in Germany, engineers are already focusing on developing treatment stages that are capable of removing pharmaceutical residues and microplastics from wastewater. In many parts of the world, however, wastewater still poses a significant risk of infection. This must be reduced, which is why germ elimination must have priority in the planning of a wastewater treatment plant, but preferably not by still chlorinating the effluents.

It has been widely documented that constructed wetlands are very good at reducing fecal coliforms. We were able to demonstrate this observation impressively at one of our wastewater treatment plants in Paraguay. Since July 2014, a constructed wetland treats wastewater from a chicken slaughterhouse. The plant is designed for 400 m³/d, but is charged with up to 800 m³/d daily. The plant is sampled monthly, which shows that the germ reduction works very well even at hydraulic overload.