SYSTEM FOR RECOVERING PHOSPHORUS FROM RAW WATER TO BE TREATED, METHOD FOR RECOVERING PHOSPHORUS FROM RAW WATER TO BE TREATED, FERTILIZER, RAW MATERIAL FOR FERTILIZER, AND RAW MATERIAL FOR YELLOW PHOSPHORUS

Adopted is a system for recovering phosphorus from raw water to be treated, the system being equipped with: a calcium dissolution reactor (1); a steel-slag feeder (3) for supplying steel slag to the calcium dissolution reactor (1); an acid feeder (4) for supplying an acid to the calcium dissolution reactor (1); a phosphorus recovery reactor (2) for recovering phosphorus from phosphorus-containing raw water to be treated, by the action of a steel-slag slurry from the calcium dissolution reactor (1); a raw-water feeder (5) for supplying the phosphorus-containing raw water to the phosphorus recovery reactor (1); a dehydrator (6) for dehydrating solid matter which has flocculated and sedimented inside the phosphorus recovery reactor (1) upon standing after the supply of the raw water and subsequent stirring for mixing; a treated-water discharge device (7) for sending outside a supernatant resulting from the reaction inside the phosphorus recovery reactor (1); and a dryer (8) for drying dehydrated matter having be