PROBLEM TO BE SOLVED: To stably achieve biological dephosphorization by using an anaerobic-aerobic circulation activated sludge treatment method.;SOLUTION: In the biological dephosphorization accelerating method using the anaerobic-aerobic circulation activated sludge treatment method, two or more theoretical stages, defined by a tracer experiment, are formed in an aerobic tank 14, circulation is performed between the theoretical stages, and the dissolved oxygen concentration of at least one of the theoretical stages is adjusted to 2 mg/L or lower, thereby the phosphorus removal rate is increased to 70 % or higher. Alternatively, two or more theoretical stages, defined by a tracer experiment, are formed in an aerobic tank 14, circulation is performed between the theoretical stages, and a dissolved oxygen concentration distribution is formed so that the standard deviation of dissolved oxygen concentrations measured at arbitrary 20 or more points in activated sludge stored in the aerobic tank 14 is 1 mg/L or more and 5 % or more of the measured values are 2 mg/L or lower, thereby the phosphorus removal rate is increased to 70 % or higher.;COPYRIGHT: (C)2004,JPO
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