In this section the theory presented in the previous sections will be used to assess the nitrogen removal capacity of an activated sludge system, for a given combination of influent characteristics and kinetic parameters values. Furthermore an optimized design procedure is developed which allows
the optimal configuration of the activated sludge system to be determined, maximizing nitrogen removal at minimum total reactor volume. The following items will be discussed:
- Determination of the nitrogen removal capacity
- Optimised design of activated sludge systems for biological nitrogen removal
(1) Determination of nitrogen removal capacity
The concepts of nitrification- and denitrication capacity will be used to determine the extent of nitrogen removal possible in an activated sludge system, given the influent nitrogen- and COD composition and the values of the kinetic parameters. First a new parameter will be introduced, i.e. the amount of nitrate available for denitrification. This parameter is defined as the fraction of the nitrification capacity that will be effectively available for denitrification in the anoxic reactor for the selected values of the mixed liquor- and sludge recirculation factors. Now, as a function of the applied sludge age, the values of nitrification capacity, nitrate available for denitrification and denitrification capacity will be compared, taking into account the maximum anoxic sludge fraction and minimum required aerobic sludge age. It will then be possible to predict the mimimum effluent nitrogen concentration- and composition, as a function of the applied sludge age. Click here to download this section.
(2) Optimised design of nitrogen removal
A variable of crucial importance is introduced: the ratio between nitrogenous and organic (COD) material in the influent. It will be demonstrated that for each value of the sludge age it can be established whether it is possible achieve complete nitrogen removal and if not, what configuration will be superior: pre-D or Bardenpho. Now, it will be easy to select the operational sludge age for which compliance to the specified effluent limits is possible and to finalize the design of the activated sludge system. Click here to download this section. Refer also to the section on the integrated cost-based design of an activated sludge system for nitrogen removal and see Example 10.5 for a design case in which the application of the design method is detailed, in conjunction with the design of the other main treatment units of the activated sludge system.