A biofilm of aerobic bacteria with a thickness of L = 0.2 mm has to be supplied with oxygen to degrade organics in wastewater. The degradation rate is limited by the oxygen concentration inside the biofilm and is not limited by the organic concentration. The concentration of dissolved oxygen is c' = c* = 3 mg L-1 O2 and it does not decrease remarkably near the boundary liquid/ solid.

Given data:

pmax = 10 d-1, X = 10 g L-1 MLSS inside the biofilm, YX/O = 0.5 g MLSS (g O2)-1, K' = 0.1 mg L-1 O2, DO2=10-6 cm2 s-1.

Calculate the efficiency coefficient รง.

166 | 7 Aerobic Treatment with Biofilm Systems Solution


Maximum oxygen uptake rate inside the biofilm:

Yo ix/02

g O2

From Fig. 7.7 for DaII = 9300 and Mo' = 30 we find: r| = 0.08.

Therefore, only 8% of the biofilm is sufficiently supplied with oxygen and is thus able to grow and to degrade the organics in the wastewater.


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