| 摘要 |
PURPOSE:To treat water drained from the semi-conductor cleaning water using an RO membrane separation device without ion-exchange process and thereby recover high purity purified water efficiently. CONSTITUTION:Water drained from the semi-conductor cleaning water is adjusted to a pH value of 6 to 9, then is biologically treated. After the elimination of turbidity, the water is adjusted to a pH value of 4 to 7 and is treated using a first RO membrane separation device 6. Further, the permeated water is adjusted to a pH value of 6 to 9 and treated using a second RO membrane separation device 8. Consequently, by using the first RO membrane separation process at a slightly to weakly acidic pH value of 4 to 7, the removal of the ions containing NH4<+> and most of the organic substances remaining even after the biological treatment are possible. After that, CO2 in the water is removed efficiently as HCO3<-> by desalting action of the second (further, a third) RO membrane separation processes at a weak alkali pH value of 7 to 9. Thus, a high-quality purified water is obtained stably and efficiently at low cost without scaling up equipment, enlarging equipment space and increasing water making cost. |
