PURPOSE: To remove SeO32- and SeO42- in waste water and to reduce the amt. of the settled concentrate to be discarded outside the system.

CONSTITUTION: A neutralizer contg. hydroxyls is added to the waste water in a primary reaction tank 1, and Cu2+ is coprecipitated and removed as the hydroxide to obtain primary treated water as the supernatant. An FeSO4 soln. is added to the primary treated water in a mixing tank 3 and sufficiently mixed, and a neutralizer is further added to a secondary reaction tank 4 to settle and concentrate the SeO32- and SeO42- remaining in the primary treated water, and the concentrate is dehydrated to a cake. Dil. sulfuric acid and iron powder are added to the cake in a dissolution tank 7 to form a selenium-contg. FeSO4 soln., and the residue contg. selenium and the soln. are separated and recovered in a filtration tank 8. Meanwhile, the filtered FeSO4 soln. is reused in the second stage.