Modelling of a recirculating granular medium filter's processes

The effluents of the French small farm factories will soon be submitted to regulation. Only few treatment techniques are available to deal with this kind of effluents (high concentration and small daily volumes). To allow the treatment, in the particular economical context of small food processing industries, the Cemagref tries to adapt a treatment based on attached growth cultures on fine media, system known to be easy to operate and relatively inexpensive. A model, based on four sub-models (hydrodynamic characteristics, oxygen transport, solute transport in the mobile and immobile phases and bacterial evolution) describes this process. Based on wastewater concentration, hydraulic load, applied organic loads, feeding / rest cycles and recycling phases number, this model predicts : eliminated organic loads and the discharge concentration in function of time, oxygen and biomass contents in function of time and depth. The determination of the model's parameters is based on a comparison between simulations and performances achieved on experimental columns. This model would be helpful in sizing full-scale filters treating different types of agro-food wastewater. The aim of this article is to present the model's structure, to give all parameters values and to compare the simulations with the results obtained on pilot and full scale plants.