Aqueous effluent treatment system (2) including a separation reactor (4) having a reactor chamber fluidly connected to an aqueous effluent source (3), connected via a pump (5) to an inlet (34) of the reactor chamber, a fluid extraction system (6) connected to a liquid effluent outlet (38) at a top of the reactor chamber, and a solid residue extraction system (8) connected to a solid residue outlet (36) at a bottom of the reactor chamber. The separation reactor is operable to generate pressures exceeding 22 MPa and temperatures exceeding 300°C in the reactor chamber configured to generate a supercritical zone (40) in an upper portion of the reactor chamber to which the liquid effluent outlet (38) is connected, and a subcritical zone (42) in a lower portion of the chamber within the reactor chamber to which the solid residue outlet (36) is connected. The solid residue extraction system comprises an output circuit (10) comprising a collector (18) coupled to the solid residue outlet via a collector input valve (V1) and to a water output tank (32) via a filter (26) and a collector liquid output valve (V4) operable to be opened to cause a pressure drop at the solid residue outlet to draw solid residue out of the reactor chamber, the solid residue extraction system further comprising a gas feed circuit (14) connected via a gas supply valve (V5) to the collector, the gas supply valve operable to be opened to extract solid residues in the collector to a solids output tank (20) connected to the collector via a collector solids output valve (V6) .