In the method of treating high-concentration organic waste water in dependence upon microorganism, waste water is first anaerobically treated in an anaerobic operation tank in dependence upon anaerobic bacteria groups and methane bacteria groups; in the second step, the waste water is further aerobically treated repeatedly in an aerobic operation tank, and an organic substance as hydrogen donor (raw waste water) is supplied to the aerobic operation tank before the succeeding aerobic treatment; in the third step, ozone treatment is effected to decolor the treated water. Two speed bacteria culture tanks for sludge bacteria and methane bacteria are provided separately to supply bacteria to the anaerobic operation tank for providing further reliable decomposition and denitrification of organic substance into methane and nitrogen gasses. |