LAUSR

Abstract The measured substrate half-saturation coefficient (KS) in Monod growth rate equation is an important parameter to calculate the specific biomass growth rate. The measured KS could be affected by both the intrinsic biomass and the external substrate transport resistance resulting in its value being called an apparent KS. Although past research recognized the effect of activate sludge (AS) floc size on the measured apparent KS due to substrate diffusional resistance, it is not clear how the floc shape affects the apparent KS. In this study, the effect of AS floc morphology in terms of both floc size and shape was examined on the measurement of apparent KS. The AS floc/granule of different morphologies (i.e., circularity and size) were generated from a 2-Dimensional computational fluid dynamics (CFD) biofilm model. Results indicate that the apparent KS was significantly larger than its intrinsic value 22 and 98 times higher for the 450 μm floc and granule, respectively, and decreased with decreasing floc size and circularity. Experimental measurement of ammonium and oxygen half-saturation coefficient of ammonium oxidizing bacteria supported the model results. This research demonstrates the importance of quantifying the AS floc shape in addition to floc size when determining the apparent KS.