Denitrification consists of several process steps. Firstly, the process breaks down the carbon, as it is the easiest to break down. PPU Umwelttechnik GmbH specialises in carrying out this process aerobically, i.e. with oxygen. Only after carbon breakdown do the microorganisms start to convert nitrogen. It is initially present in the wastewater in the form of ammonium.
The aerobic process converts this into nitrite and nitrate, which, however, cannot remain in the wastewater. By adding carbon, the process activates the micro-organisms to decompose again. The oxygen they require for this comes from the nitrite and nitrate. In the last step of the process, both substances are therefore converted into nitrogen, which is a natural component of the atmosphere and therefore harmless to humans.
The most proven process here is bottom-up denitrification. The wastewater enters a fixed bed reactor to decompose the carbon. This is followed by nitrification. After two reactors, the plant returns part of the wastewater to the first reactor for carbon removal. This is only a partial flow of about 50 per cent. The carbon from the discharged wastewater is mixed with the nitrate from the second FBR reactor. The difficulty here is that the plant has to cope with a higher load in the middle section, this does not require an external carbon source.
As this wastewater has a very low oxygen content, it must not enter public waters. Firstly, it creates an oxygen-depleted zone through which fish cannot swim. This divides habitats, which can cause long-term damage to ecosystems. On the other hand, the oxygen content of the watercourse is permanently reduced, which gradually leads to the death of living organisms.