Nitrogen is one of nature’s basic building blocks and indispensable as a nutrient for all living beings. For this reason, the waste water streams of many industries contain high levels of nitrogen. These industries encompass for the most part the food and beverage industry, including yeast factories, dairies and slaughterhouses, as well as the chemical and petrochemical industry, for example fertiliser production. Mostly the nitrogen is organically bound or present as ammonium and is referred to as Total Kjeldahl Nitrogen (TKN). Nitrate may also be present, for example when nitric acid is used as a cleaning agent in the production process.
The removal of nitrogen is one of the central requirements for waste water treatment. Basically, this is done either biologically or chemically-physically by stripping or membrane filtration. This avoids excessive nitrogen input and therefore eutrophication of surface waters.
The advantage of biological separation lies in the fact that it is not a concentration but instead an elimination process. Nitrogen compounds are converted into elemental nitrogen, which escapes into the air. At the same time, this process offers the advantage of low operating costs and is therefore the method of choice today.
Biological elimination of nitrogen consists of two process steps, nitrification and denitrification. During nitrification, ammonium is oxidised to nitrate, and during denitrification, nitrate is reduced to elemental nitrogen.
While nitrification requires oxygen, denitrification can only take place in the absence of oxygen, and in the presence of nitrate and a carbon source. Therefore, these two process steps are carried out either in different basins or with intermittent aeration.
The method developed by H+E, for example, is suitable for the spatially separated BIOFIT®.N variant. Here, denitrification is normally upstream in order to use the COD in the inlet as a carbon source for denitrification. In order to achieve a high elimination rate of up to 90 per cent, an internal recirculation of up to 800 per cent from nitrification is necessary.
Which method of nitrogen elimination proves to be the most advantageous depends on many factors. These include the concentration of nitrogen, the type of nitrogen compounds, the COD content and the flow rate. Other important factors are space requirements, energy consumption and the robustness of the selected process.
H+E will be happy to offer you expert advice on this subject. Our experts evaluate alternatives in terms of investment costs and operating costs and create your turnkey plant – regardless of whether it is a new plant or an integration into complex existing plant components.
Our nitrogen elimination plants are characterised by:
- Robust process engineering
- Low operating costs
- Reliably low discharge values
