Question

In practice, the operator checks the VSS concentration in return activated sludge (RAS) at least once every shift and makes the appropriate RAS flow rate adjustment. The previous operator recorded a RAS flow rate of 240 m3/d with the VSS in RAS as 5800 mg/L. The on-duty operator determines the VSS in RAS as 5555 mg/L. What should be the RAS flow rate be adjusted to?

Answer 1

RAS flow rate recorded in the previous shift / VSS in RAS recorded in the previous shift = RAS flow rate in the present shift / VSS in RAS determined in the present shift

240 / 5800 =    RAS flow rate in the present shift / 5555

  RAS flow rate in the present shift = (240/5800) * 5555

= 229.86 m3/day $\approx$ 230 m3/d

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