Scaling Prodedure for Biofilm Processes

Abstract

This paper presents a scaling procedure for biofilm processes based on three critical parameters derived from mechanistic models and used as similitude criteria. The advantage of using similitude criteria is that the prototype and scaled processes can have the same performance (e.g., effluent concentration) when the similitude criteria are made equal, even though all the mechanistic parameters are not known and the full kinetic models have not been solved. This scaling procedure, limited to situations for which the same microorganisms and process type can be assumed, is based on waking equal the three similitude criteria needed in biofilm kinetics: (1) blofilm surface concentration, ϕ1, (2) blofilm shear loss-rate, ϕ2, and (3)mass balance, ϕ3. The three similitude criteria are necessary to give, for the prototype and scaled processes, the same flux Into the blofilm (ϕ1), the same accumulation of blofilm (ϕ2), and the same mass balance on the substrate (ϕ3). When all three criteria are equal, both processes give the same effluent quality. One key finding of the similitude procedure is that the influent concentration, So, cannot remain constant if all three similitude criteria are to be equal simultaneously. The need to alter so is most important when external mass transport resistance and blofilm shear loss are significant. It is only when external mass transport resistance or biofilm shearing is unimportant that similitude can occur with the same so in both processes This procedure was succesfully applied to scale-down of the nitrification filter of the Croissy water treatment plant (France) for laboratory studies.