JPS6144556B

PURPOSE:To stably remove phosphates from phosphate-contg. water, by providing a crystallizer tank for bringing phosphate-contg. water into contact with crystal seeds containing calcium phosphate at a pH above 6 in the presence of Ca ion, a feeder for supplying a crystallized effluent to a biofiltration tank, etc. CONSTITUTION:A calcium agent is injected into raw water after being pretreated by a pump 10 extending from a reservoir tank 8 for a calcium agent, and an alkali agent is injected from a reservoir tank 9 for an alkali agent into said raw water by a pump 11. Hence, Ca ion is made existent in the raw water, and a pH is adjusted above 6. After small amounts of precipitates such as calcium phosphate are removed in a filtration tank 5 at need, a reacted liquid is introduced into a crystallizer tank 6 equipped with crystal seeds containing calcium phosphate and brought as an upward or downward stream into contact with the crystal seeds to perform crystallization. By this crystallization, phosphates in the raw water are removed, and outflow water having a low concentration of phosphorus is obtained.