PURPOSE: To completely prevent the generation of filter bed flies and to oxidize and remove malodorous components such as hydrogen sulfide formed in a filter bed, by adding hydrogen peroxide to organic waste water and then treating the waste water in a trickling filter process.

CONSTITUTION: To organic waste water, 20W400ppm hydrogen peroxide is added, and the waste water is treated in a trickling filter process to prevent the generation of filter bed flies. The addition of hydrogen peroxide may be performed continuously or intermittently according to circumstances. The addition of hydrogen peroxide is preferably gradually carried out, while avoiding rapid addition, taking into consideration its influence on microbes. For instance, hydrogen peroxide was continuously added to a reserving vessel preceding the trickling filter bed in a manner such that its concentration became 200ppm. The generation of filter bed flies was not notified after two days since the addition, and the generation of the filter bed flies was not notified ever since.