Abstract: The invention presents a residual water treatment plant for small flows, characterized by the combination of a primary sedimentation zone followed by anoxic and aerobic packed zones, placed serially all of them, with packing, alternating descending and ascending flows and aerated according to the oxygen requirement, there being a recirculation of treated water with sedimented mud between the secondary sedimentator and the first anoxic compartment or primary sedimentation zone, which produces treated water with enough quality for reutilization activities, after prior disinfecting (for example, watering, automobile-washing, flushing of sanitary facilities, floor-washing, and so forth). The plant requires the use of a low energy consumption air compressor, especially specified to minimize its maintenance and noise. The treatment microplant has a compact design, which requires a small area (of the size of a water cistern for 1100L, 1.