Abstract: 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 (2), which comprises a bottom (1a), a cover (1b) and walls (1c, 1d). 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 91b0 openable from above and/or openable wall (1c, 1d) to allow waste material to be loaded into the reactor.