Hydrodynamic behaviour of full scale trickling filters

In the trickling filter process, knowledge of the hydrodynamic behaviour is essential for accurate mechanistic modelling. Numerous measurements including the mean residence time, the free draining volume and the residence time distribution (RTD) have been performed in other studies. However, these results have often been obtained at pilot scale, and there is still a lack of data for the full scale process. In the present work, eight full scale plastic-packed or stone-packed trickling filters receiving urban wastewater are studied. The free draining volume and the mean residence time obtained are used together with the literature data to find correlations. Despite the variety of operating conditions of the filters, correlations are established for the stone-packed filters as well as for the vertical and random plastic-packed filters. The RTDs were assessed from tracer experiments using injections of lithium chloride. In order to explain the observed RTDs, an hydrodynamic model is developed assuming that the tracer is transported by an axially dispersed plug flow and by diffusion in and out of the biomass. Model fitting permits to identify the volume of biomass and circulating liquid in the filter.