Abstract: A process and a device for biologically treating an organic waste mixture containing organically polluted waste water and solid components. The process and the device involve exposing the organic waste mixture to a first decomposition stage where the solid components and the waste water are separated from one another and where the solid components are decomposed under predominantly aerobic conditions. The waste water is then passed to a second decomposition stage where the waste water is decomposed under anoxic conditions. Thereafter, the waste water is passed to a third decomposition stage where the waste water is decomposed again under aerobic conditions thereby creating recirculation water. At least a portion of the recirculation water is returned from the third decomposition stage to the first decomposition stage for continuously recirculating water through and between respective decomposition stages.