## X2

1070 + 2900 3970 mg/l

3. Calculate the required detention time:

Required volume = 0.05 mgd (18) = 0.9 mg = 120,000 ft3

4. Calculate the oxygen requirements. Compute the average oxygen requirement by calculating the area under the curve in Figure 7.44.8 and dividing it by the design detention time.

Area under the oxygen curve Average daily use

7310 mg/l O2 7310/18 406 mg/l day

Similarly, estimate the average VSS during a test period to determine the specific oxygen requirements.

Area under curve Average VSS concentration Specific oxygen utilization

43,040 day-mg/l 2390 mg/l 406/2390 0.17 mg/mg/day

The total oxygen requirements based on an average VSS concentration X2 in the digester effluent of 3970 mg/l are then:

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