NOVELTY - The reactor (1) comprises a three-phase separating device (11) intended for separating gas, liquid and solid of a three-phase mixture and having an inlet gate that is horizontally flowable, an outflow device (15), over which the liquid is conductible from the three-phase mixture, and a deflection device, which enforces a flow deflection between the inlet gate and outflow device. The deflection device is formed by a vertically arranged immersion wall over a water surface of the reactor. The separating device has a downwardly tapering funnel-shaped sediment collecting container (12).    USE - Reactor for the anaerobic treatment of liquids such as wastewater or aqueous solutions through anaerobic biological conversion of organic matters and/or impurities by granulated and/or flaked biomass fixed on fluidizable carrier materials.    ADVANTAGE - The reactor ensures efficient and continuous anaerobic treatment of the liquids with high volume-specific turnover rates in an improved manner.    DETAILED DESCRIPTION - The reactor (1) comprises a three-phase separating device (11) intended for separating gas, liquid and solid of a three-phase mixture and having an inlet gate that is horizontally flowable, an outflow device (15), over which the liquid is conductible from the three-phase mixture, and a deflection device, which enforces a flow deflection between the inlet gate and the outflow device. The deflection device is formed by a vertically arranged immersion wall over a water surface of the reactor. The three-phase separating device has a downwardly tapering funnel-shaped sediment collecting container (12), and a downwardly aligned sediment discharge, which has a gas deflector at its lower side. The sediment discharge connects itself to the sediment collecting container in the lower region. The separating device is formed by flat sheets or plates that are welded with one another, and has a mirror-symmetrical construction. The inlet gate is formed by slitting or perforating the sheets or plates. The immersion wall is arranged in the separating device between the inlet gate and the outflow device. The outflow device is concentrically arranged in the separating device. Several gas separators are arranged in the area of 20-65% of the reactor total height and arranged below the separating device, and have a downwardly open profile with undulated or profiled edges for gas separation. A gas riser (6) is connected to the gas separator and is parallely switched to the reactor. The reactor and the gas riser form communicating tubes. A connection takes place between the gas separators over a connecting line, in which a gas pillow forms. A blockable exhaust line is arranged in the lower part of the reactor for connecting the reactor to the gas riser.    DESCRIPTION OF DRAWING(S) - The diagram shows a longitudinal section of a reactor.    Reactor (1)    Gas riser (6)    Three-phase separating device (11)    Sediment collecting container (12)    Outflow device. (15)