Design Modelling of Combined Nitrification and Predenitrification Systems

Two mathematical steady-state models for the design of biological single sludge systems aimed at nitrogen degradation are proposed. The attention is focused on the combined nitrification system and the pre-denitrification system, considering three substrates (soluble and particulate biodegradable organic matter and ammonia nitrogen) and four substrates (the above cited and nitrate nitrogen), respectively. If both the influent flow composition and the kinetic parameters are known and the effluent nitrogen concentrations are fixed, the combined nitrification model gives an explicit expression of the biological phase volume. The pre-denitrification model makes it possible: i) to define the applicability of the system; ii) as in the previous case, to express in explicit terms the biological reactor volumes. Model applications show the increase of the oxidation phase volume, which is necessary either to face a higher influent organic load or to achieve a higher nitrogen ammonia removal.