PURPOSE: To stabilize MLSS concentration within an aerating tank by a method wherein, in case of determining a proper value of a flow amount of returned sludge by calculation, the said value is determined according to an inflow sewage amount other than MLSS concentration within an aerating tank when time variation ratio of an inflow sewage amount is high.
CONSTITUTION: An inflow sewage amount is measured by a flow meter 10 provided to a water conduit 1 and this output is supplied to a time variation ratio detecting circuit 11 of an inflow sewage amount and the output thereof is applied to a calculating circuit 12. To this circuit 12, a preselected value according to an inflow sewage amount is applied from a setting value input terminal 13, 13' and its calculating output is applied to a calculating circuit 14. To this circuit 14, an output from a circuit 15 detecting a before 24hrs. average value of an inflow sewage amount, an output of a flow meter 10, an output of an MLSS concentration meter 16 within on aerating tank, an output of a returned sludge concentration meter 17 and an MLSS concentration setting value from a setting value input terminal 18 are applied to calcualate a returned sludge flow amount proper value. This output is applied to a controller 19 to adjust a flow amount of returned sludge.
SHIBAZAKI KAZUO
YAMANAKA NAO
INABA RIYUUICHI
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