PROBLEM TO BE SOLVED: To provide an inexpensive decoloring technique for colored wastewater by utilizing a simple method using sulfur.
SOLUTION: Inflow water is introduced into a reaction tank 1, which houses a filter medium 2 filled with sulfur or a mixed particulate material of sulfur and calcium carbonate, after the pH thereof is adjusted to 8-9 or as it is. Air is passed through a filler comprising the mixed particulate material of sulfur and calcium carbonate in an ascending flow state at least under a condition of 1.0 m3/m3min so as to directly come into contact with the filler to bring about aerobic sulfur oxidizing condition due to sulfur oxidizing bacteria under an aerobic condition and a color component is oxidized and decomposed to be decolored. A pH meter 8 and a stirrer 9 are provided in order to adjust the pH of inflow water in this apparatus and a pH adjusting tank 7 is further provided through a storage tank 10 and a supply pipe 11 so as to automatically supply an acid or alkali to adjust the inflow water to predetermined pH. Decolored discharge water 5 is discharged after adjusted in pH if necessary.