The microbial degradation of hydrocarbon contaminants in soil is often limited by a lack of oxygen and poor bioavailability of contaminants. An approach to solve these problems is treating the soil in a rotary drum reactor with grinding beads. The treatment can be performed periodically or continuously and results in mixing of the soil and, thus, sufficient aeration. The grinding beads prevent ail agglomeration of the moist soil, if the moisture content is kept slightly above the plastic limit, which corresponds to the moisture content of maximum microbial activity. Furthermore, the grinding beads cause a mechanical stress to the soil, leading to a release of organic compounds to the soil water and an opening of pores which were previously inaccessible to microorganisms. Thus, the mechanical stress leads to an increased microbial activity of limited duration but exceeding the stress duration itself. In order to reach a high microbial activity lasting for a longer time, periodical mechanical stress is suitable to prevent simultaneous consolidation of the soil which results in a decreased aeration and, therefore, a lower microbial activity. In summary, a faster degradation of contaminants in soil can be achieved by treatment in a rotary drum reactor with grinding beads.