Denitrification is a process to remove nitrite and nitrate from wastewater. Various process technologies are used that lead to this result via intermediate steps.
Nitrogen removal is particularly important in areas where nutrient neutrality is required.
Nitrate compounds in groundwater are particularly harmful to humans because they are carcinogens. Plants, in turn, need them for their growth. Farmers and operators of large greenhouses in particular take advantage of this by fertilising their plants, thus supplying them with nitrates. In rural areas, this is usually done by spreading liquid manure on the fields. If farmers apply too much fertiliser, nitrates can enter the groundwater. Denitrification removes nitrates from wastewater before they contaminate the environment.
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The first advantage of denitrification is cost savings if the company discharges treated wastewater indirectly through the municipal wastewater treatment plant. They determine the amount of carbon, nitrogen and phosphorus that may be present in the wastewater. The more restrictions a company observes, the cheaper it is to discharge the wastewater to the municipal wastewater treatment plant. Therefore, the client decides to denitrify in order to gain significant savings in wastewater discharge to the municipal wastewater treatment plant.
The second advantage is the company’s environmental contribution. The wastewater leaving the plant site is treated and does not pollute the environment to the same extent as before the treatment. Furthermore, the process technology is a purely biological process without the use of machine technology or membrane processes. This keeps maintenance efforts to a minimum.
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.
