PURPOSE: To stably and efficiently adsorb and remove org. alkali in a strong acidic cation exchange (SC) column by passing semiconductor washing waste water containing org. alkali discharged from a semiconductor manufacturing process through the SC column.

CONSTITUTION: Semiconductor washing waste water containing org. alkali is successively passed through an activated carbon bed 1, a weak basic anion exchange resin bed 2, a strong basic anion exchange resin bed 3 and a strong acidic cation exchange bed 4. Therefore, by providing the SA bed 3 to the front stage of the SC bed 4, the pH of the inflow water to the SC bed becomes stable and can be always held to an alkali side without being affected by the fluctuations of anion load and the adsorption and removal of org. alkali is made stable and efficient.