In order to examine the effect of multi-stage flash distillation on the conversion of polluted sea water, fundamental experiments and quality test of fresh water were carried out. The plant used in this study was a coal mining company in Ikeshima, Nagasaki, and has a distilling capacity of 2650 ton/day. The results were as follows : 1) It was possible to prevent the NH3-N distillation completely when the pH value of sea water was adjusted to 4.0 with sulfuric acid. 2) Efficency of purification of sea water by this plant was excellent, but total hardness, Cl-, PO3-4, and metaphosphate of supply water were higher than those of total distilled water, because of the addition of metal-masking reagents and brine water in this supply water.
