第4章 生物膜动力学.ppt

第4章 生物膜动力学 Chapter 4 Biofilm Kinetics The Idealize biofilm 理想生物膜 Substrate phenomena At any position inside the biofilm,Substrate utilization: The substrate is transported into the biofilm by molecular diffusion, give by Fick’s second law: rdiff =rate of substrate accumulation due to diffusion(MsL-3T-1) For a steady-state concentration profile in the biofilm. The substrate mass balance is: The equation requires two boundary conditions: no flux into the attachment surface At the biofilm/water interface, the external mass transport is described according to Fick’s first law: D:molecular diffusion coefficient in water Illustration for First-order Kinetics General solution when Sw is known The biofilm itself At a position inside the biofilm, a mass balance on active biomass is: The steady-state biofilm 虽然生物膜内部生物增长随所处位置不同有净增长和减少，但对生物膜整体来讲，仍然可以应用稳态的概念，即单位面积上的生物膜量是常数（XfLf不随时间变化)。即表示生物量的方程延生物膜总厚度积分等于零： The steady-state –biofilm solution Substrate mass balance equation: How steady-state biofilm respond to changes in substrate concentration S: 需要估计的参数： Biomass density Xf: 5-200 mgVS/cm3, typical=40 mgVS/cm3 Diffusion coefficient in water, D (handbooks); Diffusion coefficient in the biofilm, Df=0.8D; Thickness of the effective diffusion layer: L=D/km km质量传递系数 Or: The overall biofilm-loss coefficient b’=b+bdet bdet=specific biofilm-detachment loss coefficient(T-1) (It is related to the shear stress .) Average biofilm SRT Completely mixed biofilm reactor * * Bruce E.Rittmann and Perry L. McCarty, Environmental Biotechnology:Principles and Applications. pp207-230 Bulk liquid Diffusion layer Biofilm L Xf, density（ MxL-3） Lf,thickness Full penetrated shallow Deep s s ss Sw s sf z Physical propertes Characreristic concentration profiles T