TREATMENT OF CHROMIC ACID CONTAINING WASTE WATER

PURPOSE:To prevent the lowering of capacity of a reverse smosis membrane and to enable high concentration to enhance operational reliability by a method wherein a reductant is added to a chromic acid containing waste water and the resulting treated waste water is introduced into a reverse osmosis apparatus to be subjected to concentrating treatment. CONSTITUTION:A reductant from a reductant tank 4 and a pH adjusting liquid from a pH adjusting tank 5 are added to a conditioning tank 3 according to values preliminarily set by a redox potential controller 6 and a pH controller 7 and the resulting mixture is stirred by a stirrer 8. Waste water wherein hexavalent chromium is reduced trivalent chromium by adding the reductant is introduced into a reverse osmosis apparatus 9 to be separated into purified permeate and concentated water. The latter is combined with waste water supplied from the conditioning tank 3 and the formed mixture is again introduced into the reverse osmosis apparatus 9 and, when waste water is gradually concentrated and predetermined concentration value is obtained, concentrated water is discharged from a concentrated water discharge pipe 12. During this time, the permeate is discharged from a permeate discharge pipe 13.