Theoretical investigation of particle deposition in biofilm systems

Experience has shown that the performance of biofilm reactors is strongly influenced by the size distribution of the constituents being biologically oxidized. Processes of diffusion, interception, and sedimentation that affect the transport of solid particles are presented and applied to biofilm systems. Biofilm systems with media of small diameter or long hydraulic residence time (fixed-bed, soil treatment, and fluidized-bed) can be effective for removing submicron particles through diffusion and interception. In systems with horizontal biofilm surface area, large particles (> 10–50 μm) can be removed by sedimentation. The slow mass transfer of particulate BOD can cause biodegradation rates to be much slower than for soluble species. An understanding of particle behavior will facilitate development of better models of biofilm systems. Areas that merit further research are indicated.