Modelling the dynamics of a trickling filter for waste water treatment

This study concerns the dynamics of the nitrifying efficiency of a trickling filter for waste water treatment. In a novel approach, based on minimum plant area usage, a filter will be placed after the secondary sedimentation tanks with recirculation to the activated sludge process stage. The objective of the trickling filter model is to describe the growth of the nitrifying bacteria Nitrosomonas and Nitrobacter in the bio-film. A steady state mass-balance model for the substrates in the film based on Monod kinetics has been formulated. The dynamics of the filter, or the “memory”, is described by a division of the film in four volume fractions, Nitrosomonas, Nitrobacter, inert (non-active) material and water. These fractions are calculated at different depths of the film as well as for various layers of the filter structure. Data from a pilot plant at Rya treatment plant in Gothenburg, Sweden, have provided the necessary feedback for calculating model parameters, verifying assumptions etc. A shooting and matching routine in the NAG Fortran library is used for the solution of the model equations. Simulations performed so far have indicated that it can take days and even weeks for changes in the bacteria populations to take place. This means that the working point for the proposed full scale filter at the plant should track the past history of the filter