Abstract: Method and device for treating a liquid effluent, in which this effluent enters a vessel. An intermediate level of liquid in the vessel is detected; an influx of a dilution liquid into the vessel is instigated; a high level of liquid in the vessel is detected; the influx of dilution liquid is stopped and a discharge of the fluid is instigated; a low level of liquid in the vessel is detected; the discharge of the liquid is stopped; and, while it is being discharged, the discharged liquid is exposed to light radiation in at least one treatment channel.