The Use of Accumulation of Nitrite in Biological Treatment of Wastewater

Abstract

Purpose of review

Nitrogen compounds are important pollutants of waste water. A common method of nitrogen removal from waste water is biological nitrification/denitrification. The method is not applicable to all types of waste water. Very problematic is, for example, its application to waste water with a low COD/nitrogen concentration ratio. For this type of waste waters, the nitritation/denitritation method was developed, which is based on nitrite accumulation during nitrification. The method is a shortcut version of the nitrification/denitrification process. The nitrogen removal proceeds in this case through nitrite.

Findings

The nitritation/denitritation method was tested on laboratory scale as an alternative to separate biological treatment of the sludge liquor formed in dewatering of digested sludge. No significant production of nitrate was observed in the laboratory model. The nitrate nitrogen concentration was lower than 30 mg l⁻¹ whereas the nitrite nitrogen concentration reached several hundreds of mg l⁻¹. As the carbon source for the denitritation process was used primary sludge from a waste water treatment plant, which led to a decrease in operating costs. Due to controlled conditions in the nitritation and denitritation reactors, the ammonia removal efficiency was higher than 90 %.

Conclusions

The nitritation/denitritation process is a promising method of ammonia removal from waste waters with low COD/N concentration ratios. A high ammonia concentration and loading rate in the nitritation reactor are the important factors for nitrite accumulation, which is necessary for the process.