Mass Transfer Gas Liquid is Ratelimiting

The mass balance for oxygen at the outer surface of the biofilm is:

^_^_q v_^_q rate of rate of transport consumption

160 | 7 Aerobic Treatment with Biofilm Systems Using the known yield coefficient:

we must calculate rs to obtain r'.

In case (a), c' (at the biofilm surface) may be very low compared to c* but large compared with K' (c'p K'). Therefore, we can write:

The oxygen consumption rate r' and consequently the substrate removal rate rs are limited only by mass transfer (Fig. 7.6, curve I).

In case (b), c' may be very low compared with c* but not large compared with K'. For oxygen balance, it follows that:

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