Solution

1. To calculate the required air flow rate, we start with an oxygen balance:

with 20% oxygen utilization c02,0 - c02 = 0.046 kg m-3. Starting from an NH4 balance:

8.17

can be calculated.

As NH+ + 2O2 ^ NO3 + 2 H+ + H2O, the oxygen consumption rate of nitrification is:

rO2,N = 2 ■ 0.584 = 1.17 mmol L-1 h-1 = 1.17 ■ 32 = 37.44 mg L-1 h-1 O2

= 37.44 + 33.78 (see: problem 11.1) = 71.22 g m-3 h-1 O2

For the flow rate we obtain: 71.22 ■ 5000 g m3 m3

0.046

m3 h kg

2. The concentration of dissolved oxygen must be increased from c' = 1 mg L-1 (only carbon removal) to 2 mg L-1 (carbon removal with nitrification).

What is the old and what do we select for the new specific mass transfer coefficient kLa of the aeration system? Saturation concentration c* = 9 mg L-1 O2.

(b) C-removal with nitrification kLa(c*-c ') = ro2z 71.22

The aeration system must be selected according to these requirements.

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