In a waste water treatment apparatus and/or method, waste water containing aminoethanol and dimethyl sulfoxide is introduced into a first denitrification tank within a first waste water treatment apparatus. Malodorous gas generated in the first waste water treatment apparatus is decomposed and treated in a second waste water treatment apparatus where another waste water is treated as another system. The second waste water treatment apparatus has a second nitrification tank including a semi-anaerobic section. The malodorous gas is introduced from the first waste water treatment apparatus into a scrubber. The malodorous gas is treated by sludge which is circulated between the second nitrification tank and the scrubber.