the invention relates to a procedure and an apparatus for microbiological treatment of waste containing harmful substances . according to the invention , the waste is loaded into a waste treatment reactor , which comprises a bottom , a cover and walls . organic matter is added to the waste and the properties of the waste material and the conditions are adjusted so as to make them favorable for bacterial activity . the waste is treated in the reactor substantially without agitation , and a sufficient amount of oxygen , moisture and / or nutrients is added into the waste material . the reactor of the invention comprises at least a cover 91 b 0 openable from above and / or openable wall to allow waste material to be loaded into the reactor . the reactor further comprises a substantially immovable sieve plate 911 ) and a pipe system placed at at least one level for the supply of oxygen , moisture , nutrients and / or steam while the waste material remains substantially immovable in the reactor during the treatment . the apparatus substantially permits transportation to the place of waste treatment .