Modelling population shifts in a nitrifying biofilm reactor
Résumé
Biological nitrogen removal from wastewater can be considered as a proven technology and has been widely implemented. Cost savings in terms of aera-tion and carbon source addition are realized when ammonium is oxidized to nitrite and further oxidation to nitrate is prevented. This is possible by act-ing on the difference in oxygen affinity between ammonium oxidizers (AOB) and nitrite oxidizers (NOB). This contribution deals with the modeling of microbial population shifts in a nitrifying biofilm reactor of the ITBR type (Inverse Turbulent Bed Reactor). Experimental evidence shows that different process conditions result in a different nitrifying performance, both on a macroscopic level (in terms of concentrations) and from a microbiological point of view (with respect to the selection of different types of bacteria). In this study, steady state and dynamic simulations of the ITBR reactor were performed with a 1-dimensional model, incorporating microbial diversity (2 AOB and 1 NOB). This model takes into account spatial variations in one direction (perpendicular to the substratum), in contrast to a previously de-scribed 0-dimensional model, to better describe the experimental results. The insights gained can be used to develop process control strategies acting on the microbial populations. Furthermore, extension of the presented model with more than two competing species is straightforward and not limited to nitrification processes.