A model for simultaneous particulate and dissolved substrate removal in a biofilm reactor

The present kinetic study develops a model describing zero-order soluble substrate (methanol) diffusion and biochemical reaction inside the porous biofilm matrix with simultaneous particle removal by bioflocculation at the surface of aerobic biological films. Methanol (CH₃OH) served as the dissolved substrate and native corn starch served as the organic particulates; 95% of the particles were less than a 23.9-micron equivalent spherical diameter, the median particle diameter was 14.1 microns, and only 5% of the particles were less than 1.4 microns. A bench-scale completely mixed rotating disc biofilm reactor was used to grow and experimentally measure substrate removal, both dissolved and particulate, as a function of the ratio of external biofilm area to bulk liquid volumetric flow rate, A/Q. A curve-fitting routine revealed that within the range of concentrations used in this research, internal diffusion and consumption of methanol was predicted by a zero-order reaction, and the removal of organic particulates was described by a first-order bioflocculation kinetic expression. A significant effect of the influent concentration of methanol and corn starch on the numerical value of the kinetic constants could be observed.