在生物膜中存在著如下幾個重要的過程。

1. 基質的擴散過程

2.生物膜中基質利用方程

3.生物膜中的活性生物組分變化

對于平衡狀態下的生物膜應當同時滿足以上三個方程。

解以上方程的前提是合理的選取下列參數。

K

L

Y

b'

S

上圖可以得到Steady-state的五個重要的趨勢。

1. Steady-state狀態下的生物膜損失速率biofilm loss rate等于生物膜的污泥齡SRT。 對于以某一個biofilm loss rate運行的系統來說，存在最低的基質濃度Sbmin， 可以通過下式計算

對于CSTR來說，這個操作的基質濃度是維持生物膜SRT的最低基質濃度。因此這里的與用不同的notation。如果,。With a CSTR, the effluent S value is the same at a given regardless of the influent substrate concentration. In contrast with a biofilm reactor, increasing the influent substrate concentration causes the effluent value for S to increase over ?The difference comes about because, in a CSTR, all microorganisms are exposed to the same S, while the concentration decreases with depth into a biofilm. As with any steady-state completely mixed biological process, having S lower than this critical level gives a negative growth rate and no possibility for sustaining steady-state biomass. Thus, remains a very key factor for the design and operation of both systems.

2.?J and increase very sharply (on the logarithmic scale) as S increases slightly above .?This rapid escalation occurs because J and increases?together. A small increase to S allows greater J, which allows greater , however, greater also increases J. Thus, the positive feedback among S, J, and , allows a very rapid increase in J for S slightly above .

3.?At some value of S > , the slope of J versus S declines from near infinity and approaches 1.0. This occurs at approximately S = 0.07 mg/ cm3 for the example in Figure 7.3.

4.?For S large enough, the flux becomes equal to that of a deep biofilm. The concentration signifies the spot, which is S approximately equal to 0.11 mg/cm3 in Figure 7.3. For all the steady-state biofilm is deep, or St approaches zero before the attachment surface. The practical significance of having a deep biofilm is that J no longer depends on because additional biomass does not increase the reaction rate (for the same S) when all of the added thickness has s1 = 0. On the other hand, J and Xf, increase for larger S, because the substrate concentrations inside the biofilm rise in response to a higher S.

5.?For very large S, the slope of J versus S declines gradually and eventually reaches the limiting case of one-half-order kinetics, or ? Half-order kinetics is a well-known special case for deep biofilms; it is discussed later in this chapter. The practical impact of a reaction order less than one is that increases in S give less than proportional increases in J, and marginal increases in substrate removal go down when the system is operated well into the deep region.