The authors have been engaged in the research and development concerning the recovery of MAP (Magnesium Ammonium Phosphate) using a fluidized-bed crystallized phosphorus removal system. In the reactor of the fluidized-bed crystallized phosphorus removal system, seed crystals (of MAP) are fluidized previously and new MAP crystals are produced on the seed crystal surfaces. Conventionally, the reactor consisted of one reaction tank only, but this practice had the problem that as the crystallization progresses, the seed crystal is grown excessively and as a result, the effective reaction surface areas are decreased and the fluidization effect is degraded, causing the recovery ratio to be decreased. Recently, the authors have devised a two-tank type reactor by adding a sub reaction tank to the reactor (now the main reaction tank) so that the MAP particle size in the main reaction tank may be kept constant making the recovery ratio stable. They conducted a demonstration test with a pilot experimental system of the 2-tank type reactor. For raw water T-P 111 to 507 mg/L, the main reaction tank treated water T-P 14.0 to 79.5 mg/L and phosphorus recovery ratios 84 to 92% were obtained. Because the mean MAP particle size in the main reaction tank could be kept constant, the phosphorus recovery ratio could always be above 80%, realizing stable treatment.

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