In this section the fundamental theoretical principles underlying the process of biological nitrogen removal are presented. More specific, the following issues will be discussed:
- Forms and reactions of nitrogenous material in wastewater and in the activated sludge process
- Mass balance of nitrogenous material
- Stoichometry of reactions with nitrogenous material
(1) Forms and reactions of nitrogenous material in wastewater and in the activated sludge process
Nitrogen is present in wastewater in several forms, the important ones being organic nitrogen (both soluble and particulate), ammonium/ammonia and possibly some nitrate. In the activated sludge process several reactions may occur, that will change the form of the nitrogenous matter. Figure 4.1 shows the various possibilities: ammonification, nitrification and denitrification. Click here to download this section.
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| Figure 4.1 | Schematic representation of the different forms of nitrogenous material in wastewater and their subsequent reactions in the activated sludge process |
(2) Mass balance of nitrogenous matter
In this section it will be demonstrated how to set-up a mass balance for nitrogen for a steady-state activated sludge system. The nitrogen mass balance recovery factor is introduced, which can be used to check whether the mass balance "closes". Click here to download this section. In Example 4.1 the use of the nitrogen mass balance and recovery factor are demonstrated.
(3) Stoichiometry of reactions with nitrogenous matter
The biochemical reactions involved in nitrification and denitrication result in the transfer of electrons to- and from the nitrogen atom. The oxygen consumption for nitrification and recovery of "equivalent oxygen" during denitrification are explained and quantified. Click here to download this section and here to download Example 4.2.
A second effect of the biochemical reactions in the nitrogen removal process is the consumption- and production of alkalinity. During nitrification alkalinity will be consumed and during ammonification and denitrification it will be produced. The stoichiometry of these processes, as well as the effect this will have on mixed liquor pH, will be discussed. Click here to download this section and here to download Examples 4.3 and 4.4.